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  • xcode 4 creating a 2d grid (range and domain)

    - by user1706978
    I'm learning how to program c and i'm trying to make a program the finds the range (using an equation with x as the domain) of a 2d grid...ive already attempted it, but it's giving me all these errors on Xcode, any help?(As you can see, I'm quite stuck!) #include <stdio.h> #include <stdlib.h> float domain; float domain = 2.0; float domainsol(float x ) { domain = x; float func = 1.25 * x + 5.0; return func; } int main(int argc, const char * argv[]) { }

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  • How to break closures in JavaScript

    - by Not a Name
    Is there any way to break a closure easily in JavaScript? The closest I have gotten is this: var src = 3; function foo () { return function () { return src; } } function bar (func) { var src = 9; return eval('('+func.toString()+')')(); // Line breaks closure } alert(bar(foo())); Which prints 9, instead of 3 as a closure would dictate. However, this approach seems kind of ugly to me, are there any better ways?

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  • How to fill a structure when a pointer to it, is passed as an argument to a function

    - by Ram
    I have a function: func (struct passwd* pw) { struct passwd* temp; struct passwd* save; temp = getpwnam("someuser"); /* since getpwnam returns a pointer to a static * data buffer, I am copying the returned struct * to a local struct. */ if(temp) { save = malloc(sizeof *save); if (save) { memcpy(save, temp, sizeof(struct passwd)); /* Here, I have to update passed pw* with this save struct. */ *pw = *save; /* (~ memcpy) */ } } } The function which calls func(pw) is able to get the updated information. But is it fine to use it as above. The statement *pw = *save is not a deep copy. I do not want to copy each and every member of structure one by one like pw-pw_shell = strdup(save-pw_shell) etc. Is there any better way to do it? Thanks.

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  • Path Inclusion/Global variable not working?

    - by Dan LaManna
    Simply put, my config file includes my database class, and the config file has in it: global $db; $db = new database(DB_HOST, DB_NAME, DB_USER, DB_PASS); That file is root/config.php Moving on to root/functions/func.newpage.php doesn't have any includes/requires, and uses $db-classfunction since the file I'm working with: root/newpage.php - requires the config file, as well as func.newpage.php. However I still come up with: Undefined variable db. Anything you guys are seeing I'm not? Thanks! Let me know if more details are needed.

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  • Red Hat Yum not working out of the box?

    - by Tucker
    I have a server runnning Red Hat Enterprise Linux v5.6 in the cloud. My project constraints do not allow me to use another OS. When I created the cloud server, I was able to SSH into it and access the shell. I next ran the command: sudo yum update But the command failed. About a month ago I created another server with the same machine image and didn't have that error. Why is it failing now? The following is the terminal output sudo yum update Loaded plugins: security Repository rhel-server is listed more than once in the configuration Traceback (most recent call last): File "/usr/bin/yum", line 29, in ? yummain.user_main(sys.argv[1:], exit_code=True) File "/usr/share/yum-cli/yummain.py", line 309, in user_main errcode = main(args) File "/usr/share/yum-cli/yummain.py", line 178, in main result, resultmsgs = base.doCommands() File "/usr/share/yum-cli/cli.py", line 345, in doCommands self._getTs(needTsRemove) File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 101, in _getTs self._getTsInfo(remove_only) File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 112, in _getTsInfo pkgSack = self.pkgSack File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 662, in <lambda> pkgSack = property(fget=lambda self: self._getSacks(), File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 502, in _getSacks self.repos.populateSack(which=repos) File "/usr/lib/python2.4/site-packages/yum/repos.py", line 260, in populateSack sack.populate(repo, mdtype, callback, cacheonly) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 168, in populate if self._check_db_version(repo, mydbtype): File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 226, in _check_db_version return repo._check_db_version(mdtype) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1233, in _check_db_version repoXML = self.repoXML File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1406, in <lambda> repoXML = property(fget=lambda self: self._getRepoXML(), File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1398, in _getRepoXML self._loadRepoXML(text=self) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1388, in _loadRepoXML return self._groupLoadRepoXML(text, ["primary"]) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1372, in _groupLoadRepoXML if self._commonLoadRepoXML(text): File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 1208, in _commonLoadRepoXML result = self._getFileRepoXML(local, text) File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 989, in _getFileRepoXML cache=self.http_caching == 'all') File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 826, in _getFile http_headers=headers, File "/usr/lib/python2.4/site-packages/urlgrabber/mirror.py", line 412, in urlgrab return self._mirror_try(func, url, kw) File "/usr/lib/python2.4/site-packages/urlgrabber/mirror.py", line 398, in _mirror_try return func_ref( *(fullurl,), **kwargs ) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 936, in urlgrab return self._retry(opts, retryfunc, url, filename) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 854, in _retry r = apply(func, (opts,) + args, {}) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 922, in retryfunc fo = URLGrabberFileObject(url, filename, opts) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1010, in __init__ self._do_open() File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1093, in _do_open fo, hdr = self._make_request(req, opener) File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1202, in _make_request fo = opener.open(req) File "/usr/lib64/python2.4/urllib2.py", line 358, in open response = self._open(req, data) File "/usr/lib64/python2.4/urllib2.py", line 376, in _open '_open', req) File "/usr/lib64/python2.4/urllib2.py", line 337, in _call_chain result = func(*args) File "/usr/lib64/python2.4/site-packages/M2Crypto/m2urllib2.py", line 82, in https_open h.request(req.get_method(), req.get_selector(), req.data, headers) File "/usr/lib64/python2.4/httplib.py", line 810, in request self._send_request(method, url, body, headers) File "/usr/lib64/python2.4/httplib.py", line 833, in _send_request self.endheaders() File "/usr/lib64/python2.4/httplib.py", line 804, in endheaders self._send_output() File "/usr/lib64/python2.4/httplib.py", line 685, in _send_output self.send(msg) File "/usr/lib64/python2.4/httplib.py", line 652, in send self.connect() File "/usr/lib64/python2.4/site-packages/M2Crypto/httpslib.py", line 47, in connect self.sock.connect((self.host, self.port)) File "/usr/lib64/python2.4/site-packages/M2Crypto/SSL/Connection.py", line 174, in connect ret = self.connect_ssl() File "/usr/lib64/python2.4/site-packages/M2Crypto/SSL/Connection.py", line 167, in connect_ssl return m2.ssl_connect(self.ssl, self._timeout) M2Crypto.SSL.SSLError: certificate verify failed

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  • How to remove MySQL completely with config and library files on ubuntu 12.04 gnome 3.0

    - by codeartist
    I tried everything till now: sudo apt-get remove mysql-server mysql-client mysql-common sudo apt-get purge mysql-server mysql-client mysql-common sudo apt-get autoremove and even more commands... But whenever I am trying to locate mysql. I get a no. of files related to mysql command: shell>> locate mysql Output: /etc/mysql /etc/apparmor.d/usr.sbin.mysqld /etc/apparmor.d/abstractions/mysql /etc/apparmor.d/cache/usr.sbin.mysqld /etc/apparmor.d/cache/usr.sbin.mysqld-akonadi /etc/apparmor.d/local/usr.sbin.mysqld /etc/bash_completion.d/mysqladmin /etc/init/mysql.conf /etc/logcheck/ignore.d.paranoid/mysql-server-5_5 /etc/logcheck/ignore.d.server/mysql-server-5_5 /etc/logcheck/ignore.d.workstation/mysql-server-5_5 /etc/logrotate.d/mysql-server /etc/mysql/conf.d /etc/mysql/debian-start /etc/mysql/debian.cnf /etc/mysql/conf.d/mysqld_safe_syslog.cnf /home/pkr/.mysql_history /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,libqt4-sql-mysql,,349051c3a57da571aa832adb39177aff /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,mysql-client,,cbf77a486cdc80547317981a33144427 /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,mysql-client,,de8220dee4d957a9502caa79e8d2fdda /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,any,any,any,libqt4-sql-mysql,page,1,helpful,,17fb2e657321dc51526ee8fe9928da30 /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,any,any,any,mysql-client,page,1,helpful,,a4c1b6e8200f36ab5745c6f81f14da0a /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,oneiric,any,libqt4-sql-mysql,page,1,helpful,,c54295fb82b8183350cd34f22c3547ef /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,oneiric,any,mysql-client,page,1,helpful,,fcf201c1abff3f774af89173a84de2cc /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,precise,any,libqt4-sql-mysql,page,1,helpful,,0cd86648584efeccfb16119012f89540 /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,precise,any,mysql-client,page,1,helpful,,eb84724e9da7851ff8862a227d8bac59 /home/pkr/.local/share/akonadi/mysql.conf /home/pkr/.local/share/akonadi/db_data/mysql /home/pkr/.local/share/akonadi/db_data/mysql.err /home/pkr/.local/share/akonadi/db_data/mysql.err.old /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/db.MYD /home/pkr/.local/share/akonadi/db_data/mysql/db.MYI /home/pkr/.local/share/akonadi/db_data/mysql/db.frm /home/pkr/.local/share/akonadi/db_data/mysql/event.MYD /home/pkr/.local/share/akonadi/db_data/mysql/event.MYI /home/pkr/.local/share/akonadi/db_data/mysql/event.frm /home/pkr/.local/share/akonadi/db_data/mysql/func.MYD /home/pkr/.local/share/akonadi/db_data/mysql/func.MYI /home/pkr/.local/share/akonadi/db_data/mysql/func.frm /home/pkr/.local/share/akonadi/db_data/mysql/general_log.CSM /home/pkr/.local/share/akonadi/db_data/mysql/general_log.CSV /home/pkr/.local/share/akonadi/db_data/mysql/general_log.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_category.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_category.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_category.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.frm /home/pkr/.local/share/akonadi/db_data/mysql/host.MYD /home/pkr/.local/share/akonadi/db_data/mysql/host.MYI /home/pkr/.local/share/akonadi/db_data/mysql/host.frm /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.MYD /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.MYI /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.frm /home/pkr/.local/share/akonadi/db_data/mysql/plugin.MYD /home/pkr/.local/share/akonadi/db_data/mysql/plugin.MYI /home/pkr/.local/share/akonadi/db_data/mysql/plugin.frm /home/pkr/.local/share/akonadi/db_data/mysql/proc.MYD /home/pkr/.local/share/akonadi/db_data/mysql/proc.MYI /home/pkr/.local/share/akonadi/db_data/mysql/proc.frm /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/servers.MYD /home/pkr/.local/share/akonadi/db_data/mysql/servers.MYI /home/pkr/.local/share/akonadi/db_data/mysql/servers.frm /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.CSM /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.CSV /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.frm /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.frm /home/pkr/.local/share/akonadi/db_data/mysql/user.MYD /home/pkr/.local/share/akonadi/db_data/mysql/user.MYI /home/pkr/.local/share/akonadi/db_data/mysql/user.frm /usr/bin/mysql /usr/bin/mysql_install_db /usr/bin/mysql_upgrade /usr/bin/mysqlcheck /usr/sbin/mysqld /usr/share/mysql /usr/share/app-install/desktop/gmysqlcc:gmysqlcc.desktop /usr/share/app-install/desktop/mysql-client.desktop /usr/share/app-install/desktop/mysql-navigator:mysql-navigator.desktop /usr/share/app-install/desktop/mysql-server.desktop /usr/share/app-install/icons/gmysqlcc-32.png /usr/share/app-install/icons/mysql-navigator.png /usr/share/doc/mysql-client-core-5.5 /usr/share/doc/mysql-server-core-5.5 /usr/share/kde4/apps/katepart/syntax/sql-mysql.xml /usr/share/man/man1/mysql.1.gz /usr/share/man/man1/mysql_install_db.1.gz /usr/share/man/man1/mysql_upgrade.1.gz /usr/share/man/man1/mysqlcheck.1.gz /usr/share/man/man8/mysqld.8.gz /var/cache/apt/archives/akonadi-backend-mysql_1.7.2-0ubuntu1_all.deb /var/cache/apt/archives/libmysqlclient-dev_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/libmysqlclient18_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/libqt4-sql-mysql_4%3a4.8.1-0ubuntu4.1_i386.deb /var/cache/apt/archives/mysql-client-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-client-core-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-client_5.5.22-0ubuntu1_all.deb /var/cache/apt/archives/mysql-common_5.5.22-0ubuntu1_all.deb /var/cache/apt/archives/mysql-server-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-server-core-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-server_5.5.22-0ubuntu1_all.deb /var/lib/dpkg/info/mysql-client-core-5.5.list /var/lib/dpkg/info/mysql-client-core-5.5.md5sums /var/lib/dpkg/info/mysql-server-5.5.list /var/lib/dpkg/info/mysql-server-5.5.postrm /var/lib/dpkg/info/mysql-server-core-5.5.list /var/lib/dpkg/info/mysql-server-core-5.5.md5sums /var/log/mysql /var/log/mysql.err /var/log/mysql.log /var/log/mysql.log.1.gz /var/log/mysql.log.2.gz /var/log/mysql.log.3.gz /var/log/mysql.log.4.gz /var/log/mysql.log.5.gz /var/log/mysql.log.6.gz /var/log/mysql.log.7.gz /var/log/upstart/mysql.log.1.gz /var/log/upstart/mysql.log.2.gz /var/log/upstart/mysql.log.3.gz /var/log/upstart/mysql.log.4.gz /var/log/upstart/mysql.log.5.gz /var/log/upstart/mysql.log.6.gz /var/log/upstart/mysql.log.7.gz What should I do now? Please help me out in this :( I was trying to find out if there is any way I can remove mysql related every file and then reinstall mysql. I need it for Qt connectivity. I don't understand what to do! Please help :(

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  • Parallelism in .NET – Part 14, The Different Forms of Task

    - by Reed
    Before discussing Task creation and actual usage in concurrent environments, I will briefly expand upon my introduction of the Task class and provide a short explanation of the distinct forms of Task.  The Task Parallel Library includes four distinct, though related, variations on the Task class. In my introduction to the Task class, I focused on the most basic version of Task.  This version of Task, the standard Task class, is most often used with an Action delegate.  This allows you to implement for each task within the task decomposition as a single delegate. Typically, when using the new threading constructs in .NET 4 and the Task Parallel Library, we use lambda expressions to define anonymous methods.  The advantage of using a lambda expression is that it allows the Action delegate to directly use variables in the calling scope.  This eliminates the need to make separate Task classes for Action<T>, Action<T1,T2>, and all of the other Action<…> delegate types.  As an example, suppose we wanted to make a Task to handle the ”Show Splash” task from our earlier decomposition.  Even if this task required parameters, such as a message to display, we could still use an Action delegate specified via a lambda: // Store this as a local variable string messageForSplashScreen = GetSplashScreenMessage(); // Create our task Task showSplashTask = new Task( () => { // We can use variables in our outer scope, // as well as methods scoped to our class! this.DisplaySplashScreen(messageForSplashScreen); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This provides a huge amount of flexibility.  We can use this single form of task for any task which performs an operation, provided the only information we need to track is whether the task has completed successfully or not.  This leads to my first observation: Use a Task with a System.Action delegate for any task for which no result is generated. This observation leads to an obvious corollary: we also need a way to define a task which generates a result.  The Task Parallel Library provides this via the Task<TResult> class. Task<TResult> subclasses the standard Task class, providing one additional feature – the ability to return a value back to the user of the task.  This is done by switching from providing an Action delegate to providing a Func<TResult> delegate.  If we decompose our problem, and we realize we have one task where its result is required by a future operation, this can be handled via Task<TResult>.  For example, suppose we want to make a task for our “Check for Update” task, we could do: Task<bool> checkForUpdateTask = new Task<bool>( () => { return this.CheckWebsiteForUpdate(); }); Later, we would start this task, and perform some other work.  At any point in the future, we could get the value from the Task<TResult>.Result property, which will cause our thread to block until the task has finished processing: // This uses Task<bool> checkForUpdateTask generated above... // Start the task, typically on a background thread checkForUpdateTask.Start(); // Do some other work on our current thread this.DoSomeWork(); // Discover, from our background task, whether an update is available // This will block until our task completes bool updateAvailable = checkForUpdateTask.Result; This leads me to my second observation: Use a Task<TResult> with a System.Func<TResult> delegate for any task which generates a result. Task and Task<TResult> provide a much cleaner alternative to the previous Asynchronous Programming design patterns in the .NET framework.  Instead of trying to implement IAsyncResult, and providing BeginXXX() and EndXXX() methods, implementing an asynchronous programming API can be as simple as creating a method that returns a Task or Task<TResult>.  The client side of the pattern also is dramatically simplified – the client can call a method, then either choose to call task.Wait() or use task.Result when it needs to wait for the operation’s completion. While this provides a much cleaner model for future APIs, there is quite a bit of infrastructure built around the current Asynchronous Programming design patterns.  In order to provide a model to work with existing APIs, two other forms of Task exist.  There is a constructor for Task which takes an Action<Object> and a state parameter.  In addition, there is a constructor for creating a Task<TResult> which takes a Func<Object, TResult> as well as a state parameter.  When using these constructors, the state parameter is stored in the Task.AsyncState property. While these two overloads exist, and are usable directly, I strongly recommend avoiding this for new development.  The two forms of Task which take an object state parameter exist primarily for interoperability with traditional .NET Asynchronous Programming methodologies.  Using lambda expressions to capture variables from the scope of the creator is a much cleaner approach than using the untyped state parameters, since lambda expressions provide full type safety without introducing new variables.

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  • How to remove MySQL completely with config and library files?

    - by codeartist
    I tried everything till now: sudo apt-get remove mysql-server mysql-client mysql-common sudo apt-get purge mysql-server mysql-client mysql-common sudo apt-get autoremove and even more commands... But whenever I am trying to locate mysql. I get a no. of files related to mysql command: shell>> locate mysql Output: /etc/mysql /etc/apparmor.d/usr.sbin.mysqld /etc/apparmor.d/abstractions/mysql /etc/apparmor.d/cache/usr.sbin.mysqld /etc/apparmor.d/cache/usr.sbin.mysqld-akonadi /etc/apparmor.d/local/usr.sbin.mysqld /etc/bash_completion.d/mysqladmin /etc/init/mysql.conf /etc/logcheck/ignore.d.paranoid/mysql-server-5_5 /etc/logcheck/ignore.d.server/mysql-server-5_5 /etc/logcheck/ignore.d.workstation/mysql-server-5_5 /etc/logrotate.d/mysql-server /etc/mysql/conf.d /etc/mysql/debian-start /etc/mysql/debian.cnf /etc/mysql/conf.d/mysqld_safe_syslog.cnf /home/pkr/.mysql_history /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,libqt4-sql-mysql,,349051c3a57da571aa832adb39177aff /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,mysql-client,,cbf77a486cdc80547317981a33144427 /home/pkr/.cache/software-center/piston-helper/rec.ubuntu.com,api,1.0,recommend_app,mysql-client,,de8220dee4d957a9502caa79e8d2fdda /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,any,any,any,libqt4-sql-mysql,page,1,helpful,,17fb2e657321dc51526ee8fe9928da30 /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,any,any,any,mysql-client,page,1,helpful,,a4c1b6e8200f36ab5745c6f81f14da0a /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,oneiric,any,libqt4-sql-mysql,page,1,helpful,,c54295fb82b8183350cd34f22c3547ef /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,oneiric,any,mysql-client,page,1,helpful,,fcf201c1abff3f774af89173a84de2cc /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,precise,any,libqt4-sql-mysql,page,1,helpful,,0cd86648584efeccfb16119012f89540 /home/pkr/.cache/software-center/rnrclient/reviews.ubuntu.com,reviews,api,1.0,reviews,filter,en,ubuntu,precise,any,mysql-client,page,1,helpful,,eb84724e9da7851ff8862a227d8bac59 /home/pkr/.local/share/akonadi/mysql.conf /home/pkr/.local/share/akonadi/db_data/mysql /home/pkr/.local/share/akonadi/db_data/mysql.err /home/pkr/.local/share/akonadi/db_data/mysql.err.old /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/columns_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/db.MYD /home/pkr/.local/share/akonadi/db_data/mysql/db.MYI /home/pkr/.local/share/akonadi/db_data/mysql/db.frm /home/pkr/.local/share/akonadi/db_data/mysql/event.MYD /home/pkr/.local/share/akonadi/db_data/mysql/event.MYI /home/pkr/.local/share/akonadi/db_data/mysql/event.frm /home/pkr/.local/share/akonadi/db_data/mysql/func.MYD /home/pkr/.local/share/akonadi/db_data/mysql/func.MYI /home/pkr/.local/share/akonadi/db_data/mysql/func.frm /home/pkr/.local/share/akonadi/db_data/mysql/general_log.CSM /home/pkr/.local/share/akonadi/db_data/mysql/general_log.CSV /home/pkr/.local/share/akonadi/db_data/mysql/general_log.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_category.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_category.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_category.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_keyword.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_relation.frm /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.MYD /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.MYI /home/pkr/.local/share/akonadi/db_data/mysql/help_topic.frm /home/pkr/.local/share/akonadi/db_data/mysql/host.MYD /home/pkr/.local/share/akonadi/db_data/mysql/host.MYI /home/pkr/.local/share/akonadi/db_data/mysql/host.frm /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.MYD /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.MYI /home/pkr/.local/share/akonadi/db_data/mysql/ndb_binlog_index.frm /home/pkr/.local/share/akonadi/db_data/mysql/plugin.MYD /home/pkr/.local/share/akonadi/db_data/mysql/plugin.MYI /home/pkr/.local/share/akonadi/db_data/mysql/plugin.frm /home/pkr/.local/share/akonadi/db_data/mysql/proc.MYD /home/pkr/.local/share/akonadi/db_data/mysql/proc.MYI /home/pkr/.local/share/akonadi/db_data/mysql/proc.frm /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/procs_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/proxies_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/servers.MYD /home/pkr/.local/share/akonadi/db_data/mysql/servers.MYI /home/pkr/.local/share/akonadi/db_data/mysql/servers.frm /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.CSM /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.CSV /home/pkr/.local/share/akonadi/db_data/mysql/slow_log.frm /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.MYD /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.MYI /home/pkr/.local/share/akonadi/db_data/mysql/tables_priv.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_leap_second.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_name.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition.frm /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.MYD /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.MYI /home/pkr/.local/share/akonadi/db_data/mysql/time_zone_transition_type.frm /home/pkr/.local/share/akonadi/db_data/mysql/user.MYD /home/pkr/.local/share/akonadi/db_data/mysql/user.MYI /home/pkr/.local/share/akonadi/db_data/mysql/user.frm /usr/bin/mysql /usr/bin/mysql_install_db /usr/bin/mysql_upgrade /usr/bin/mysqlcheck /usr/sbin/mysqld /usr/share/mysql /usr/share/app-install/desktop/gmysqlcc:gmysqlcc.desktop /usr/share/app-install/desktop/mysql-client.desktop /usr/share/app-install/desktop/mysql-navigator:mysql-navigator.desktop /usr/share/app-install/desktop/mysql-server.desktop /usr/share/app-install/icons/gmysqlcc-32.png /usr/share/app-install/icons/mysql-navigator.png /usr/share/doc/mysql-client-core-5.5 /usr/share/doc/mysql-server-core-5.5 /usr/share/kde4/apps/katepart/syntax/sql-mysql.xml /usr/share/man/man1/mysql.1.gz /usr/share/man/man1/mysql_install_db.1.gz /usr/share/man/man1/mysql_upgrade.1.gz /usr/share/man/man1/mysqlcheck.1.gz /usr/share/man/man8/mysqld.8.gz /var/cache/apt/archives/akonadi-backend-mysql_1.7.2-0ubuntu1_all.deb /var/cache/apt/archives/libmysqlclient-dev_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/libmysqlclient18_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/libqt4-sql-mysql_4%3a4.8.1-0ubuntu4.1_i386.deb /var/cache/apt/archives/mysql-client-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-client-core-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-client_5.5.22-0ubuntu1_all.deb /var/cache/apt/archives/mysql-common_5.5.22-0ubuntu1_all.deb /var/cache/apt/archives/mysql-server-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-server-core-5.5_5.5.22-0ubuntu1_i386.deb /var/cache/apt/archives/mysql-server_5.5.22-0ubuntu1_all.deb /var/lib/dpkg/info/mysql-client-core-5.5.list /var/lib/dpkg/info/mysql-client-core-5.5.md5sums /var/lib/dpkg/info/mysql-server-5.5.list /var/lib/dpkg/info/mysql-server-5.5.postrm /var/lib/dpkg/info/mysql-server-core-5.5.list /var/lib/dpkg/info/mysql-server-core-5.5.md5sums /var/log/mysql /var/log/mysql.err /var/log/mysql.log /var/log/mysql.log.1.gz /var/log/mysql.log.2.gz /var/log/mysql.log.3.gz /var/log/mysql.log.4.gz /var/log/mysql.log.5.gz /var/log/mysql.log.6.gz /var/log/mysql.log.7.gz /var/log/upstart/mysql.log.1.gz /var/log/upstart/mysql.log.2.gz /var/log/upstart/mysql.log.3.gz /var/log/upstart/mysql.log.4.gz /var/log/upstart/mysql.log.5.gz /var/log/upstart/mysql.log.6.gz /var/log/upstart/mysql.log.7.gz What should I do now? Please help me out in this :( I was trying to find out if there is any way I can remove mysql related every file and then reinstall mysql. I need it for Qt connectivity. I don't understand what to do! Please help :(

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  • Passthrough Objects – Duck Typing++

    - by EltonStoneman
    [Source: http://geekswithblogs.net/EltonStoneman] Can't see a genuine use for this, but I got the idea in my head and wanted to work it through. It's an extension to the idea of duck typing, for scenarios where types have similar behaviour, but implemented in differently-named members. So you may have a set of objects you want to treat as an interface, which don't implement the interface explicitly, and don't have the same member names so they can't be duck-typed into implicitly implementing the interface. In a fictitious example, I want to call Get on whichever ICache implementation is current, and have the call passed through to the relevant method – whether it's called Read, Retrieve or whatever: A sample implementation is up on github here: PassthroughSample. This uses Castle's DynamicProxy behind the scenes in the same way as my duck typing sample, but allows you to configure the passthrough to specify how the inner (implementation) and outer (interface) members are mapped:       var setup = new Passthrough();     var cache = setup.Create("PassthroughSample.Tests.Stubs.AspNetCache, PassthroughSample.Tests")                             .WithPassthrough("Name", "CacheName")                             .WithPassthrough("Get", "Retrieve")                             .WithPassthrough("Set", "Insert")                             .As<ICache>(); - or using some ugly Lambdas to avoid the strings :     Expression<Func<ICache, string, object>> get = (o, s) => o.Get(s);     Expression<Func<Memcached, string, object>> read = (i, s) => i.Read(s);     Expression<Action<ICache, string, object>> set = (o, s, obj) => o.Set(s, obj);     Expression<Action<Memcached, string, object>> insert = (i, s, obj) => i.Put(s, obj);       ICache cache = new Passthrough<ICache, Memcached>()                     .Create()                     .WithPassthrough(o => o.Name, i => i.InstanceName)                     .WithPassthrough(get, read)                     .WithPassthrough(set, insert)                     .As();   - or even in config:   ICache cache = Passthrough.GetConfigured<ICache>(); ...  <passthrough>     <types>       <typename="PassthroughSample.Tests.Stubs.ICache, PassthroughSample.Tests"             passesThroughTo="PassthroughSample.Tests.Stubs.AppFabricCache, PassthroughSample.Tests">         <members>           <membername="Name"passesThroughTo="RegionName"/>           <membername="Get"passesThroughTo="Out"/>           <membername="Set"passesThroughTo="In"/>         </members>       </type>   Possibly useful for injecting stubs for dependencies in tests, when your application code isn't using an IoC container. Possibly it also has an alternative implementation using .NET 4.0 dynamic objects, rather than the dynamic proxy.

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  • The last MVVM you'll ever need?

    - by Nuri Halperin
    As my MVC projects mature and grow, the need to have some omnipresent, ambient model properties quickly emerge. The application no longer has only one dynamic pieced of data on the page: A sidebar with a shopping cart, some news flash on the side – pretty common stuff. The rub is that a controller is invoked in context of a single intended request. The rest of the data, even though it could be just as dynamic, is expected to appear on it's own. There are many solutions to this scenario. MVVM prescribes creating elaborate objects which expose your new data as a property on some uber-object with more properties exposing the "side show" ambient data. The reason I don't love this approach is because it forces fairly acute awareness of the view, and soon enough you have many MVVM objects laying around, and views have to start doing null-checks in order to ensure you really supplied all the values before binding to them. Ick. Just as unattractive is the ViewData dictionary. It's not strongly typed, and in both this and the MVVM approach someone has to populate these properties – n'est pas? Where does that live? With MVC2, we get the formerly-futures  feature Html.RenderAction(). The feature allows you plant a line in a view, of the format: <% Html.RenderAction("SessionInterest", "Session"); %> While this syntax looks very clean, I can't help being bothered by it. MVC was touting a very strong separation of concerns, the Model taking on the role of the business logic, the controller handling route and performing minimal view-choosing operations and the views strictly focused on rendering out angled-bracket tags. The RenderAction() syntax has the view calling some controller and invoking it inline with it's runtime rendering. This – to my taste – embeds too much  knowledge of controllers into the view's code – which was allegedly forbidden.  The one way flow "Controller Receive Data –> Controller invoke Model –> Controller select view –> Controller Hand data to view" now gets a "View calls controller and gets it's own data" which is not so one-way anymore. Ick. I toyed with some other solutions a bit, including some base controllers, special view classes etc. My current favorite though is making use of the ExpandoObject and dynamic features with C# 4.0. If you follow Phil Haack or read a bit from David Heyden you can see the general picture emerging. The game changer is that using the new dynamic syntax, one can sprout properties on an object and make use of them in the view. Well that beats having a bunch of uni-purpose MVVM's any day! Rather than statically exposed properties, we'll just use the capability of adding members at runtime. Armed with new ideas and syntax, I went to work: First, I created a factory method to enrich the focuse object: public static class ModelExtension { public static dynamic Decorate(this Controller controller, object mainValue) { dynamic result = new ExpandoObject(); result.Value = mainValue; result.SessionInterest = CodeCampBL.SessoinInterest(); result.TagUsage = CodeCampBL.TagUsage(); return result; } } This gives me a nice fluent way to have the controller add the rest of the ambient "side show" items (SessionInterest, TagUsage in this demo) and expose them all as the Model: public ActionResult Index() { var data = SyndicationBL.Refresh(TWEET_SOURCE_URL); dynamic result = this.Decorate(data); return View(result); } So now what remains is that my view knows to expect a dynamic object (rather than statically typed) so that the ASP.NET page compiler won't barf: <%@ Page Language="C#" Title="Ambient Demo" MasterPageFile="~/Views/Shared/Ambient.Master" Inherits="System.Web.Mvc.ViewPage<dynamic>" %> Notice the generic ViewPage<dynamic>. It doesn't work otherwise. In the page itself, Model.Value property contains the main data returned from the controller. The nice thing about this, is that the master page (Ambient.Master) also inherits from the generic ViewMasterPage<dynamic>. So rather than the page worrying about all this ambient stuff, the side bars and panels for ambient data all reside in a master page, and can be rendered using the RenderPartial() syntax: <% Html.RenderPartial("TagCloud", Model.SessionInterest as Dictionary<string, int>); %> Note here that a cast is necessary. This is because although dynamic is magic, it can't figure out what type this property is, and wants you to give it a type so its binder can figure out the right property to bind to at runtime. I use as, you can cast if you like. So there we go – no violation of MVC, no explosion of MVVM models and voila – right? Well, I could not let this go without a tweak or two more. The first thing to improve, is that some views may not need all the properties. In that case, it would be a waste of resources to populate every property. The solution to this is simple: rather than exposing properties, I change d the factory method to expose lambdas - Func<T> really. So only if and when a view accesses a member of the dynamic object does it load the data. public static class ModelExtension { // take two.. lazy loading! public static dynamic LazyDecorate(this Controller c, object mainValue) { dynamic result = new ExpandoObject(); result.Value = mainValue; result.SessionInterest = new Func<Dictionary<string, int>>(() => CodeCampBL.SessoinInterest()); result.TagUsage = new Func<Dictionary<string, int>>(() => CodeCampBL.TagUsage()); return result; } } Now that lazy loading is in place, there's really no reason not to hook up all and any possible ambient property. Go nuts! Add them all in – they won't get invoked unless used. This now requires changing the signature of usage on the ambient properties methods –adding some parenthesis to the master view: <% Html.RenderPartial("TagCloud", Model.SessionInterest() as Dictionary<string, int>); %> And, of course, the controller needs to call LazyDecorate() rather than the old Decorate(). The final touch is to introduce a convenience method to the my Controller class , so that the tedium of calling Decorate() everywhere goes away. This is done quite simply by adding a bunch of methods, matching View(object), View(string,object) signatures of the Controller class: public ActionResult Index() { var data = SyndicationBL.Refresh(TWEET_SOURCE_URL); return AmbientView(data); } //these methods can reside in a base controller for the solution: public ViewResult AmbientView(dynamic data) { dynamic result = ModelExtension.LazyDecorate(this, data); return View(result); } public ViewResult AmbientView(string viewName, dynamic data) { dynamic result = ModelExtension.LazyDecorate(this, data); return View(viewName, result); } The call to AmbientView now replaces any call the View() that requires the ambient data. DRY sattisfied, lazy loading and no need to replace core pieces of the MVC pipeline. I call this a good MVC day. Enjoy!

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  • Authenticating clients in the new WCF Http stack

    - by cibrax
    About this time last year, I wrote a couple of posts about how to use the “Interceptors” from the REST starker kit for implementing several authentication mechanisms like “SAML”, “Basic Authentication” or “OAuth” in the WCF Web programming model. The things have changed a lot since then, and Glenn finally put on our hands a new version of the Web programming model that deserves some attention and I believe will help us a lot to build more Http oriented services in the .NET stack. What you can get today from wcf.codeplex.com is a preview with some cool features like Http Processors (which I already discussed here), a new and improved version of the HttpClient library, Dependency injection and better TDD support among others. However, the framework still does not support an standard way of doing client authentication on the services (This is something planned for the upcoming releases I believe). For that reason, moving the existing authentication interceptors to this new programming model was one of the things I did in the last few days. In order to make authentication simple and easy to extend,  I first came up with a model based on what I called “Authentication Interceptors”. An authentication interceptor maps to an existing Http authentication mechanism and implements the following interface, public interface IAuthenticationInterceptor{ string Scheme { get; } bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal);} An authentication interceptors basically needs to returns the http authentication schema that implements in the property “Scheme”, and implements the authentication mechanism in the method “DoAuthentication”. As you can see, this last method “DoAuthentication” only relies on the HttpRequestMessage and HttpResponseMessage classes, making the testing of this interceptor very simple (There is no need to do some black magic with the WCF context or messages). After this, I implemented a couple of interceptors for supporting basic authentication and brokered authentication with SAML (using WIF) in my services. The following code illustrates how the basic authentication interceptors looks like. public class BasicAuthenticationInterceptor : IAuthenticationInterceptor{ Func<UsernameAndPassword, bool> userValidation; string realm;  public BasicAuthenticationInterceptor(Func<UsernameAndPassword, bool> userValidation, string realm) { if (userValidation == null) throw new ArgumentNullException("userValidation");  if (string.IsNullOrEmpty(realm)) throw new ArgumentNullException("realm");  this.userValidation = userValidation; this.realm = realm; }  public string Scheme { get { return "Basic"; } }  public bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal) { string[] credentials = ExtractCredentials(request); if (credentials.Length == 0 || !AuthenticateUser(credentials[0], credentials[1])) { response.StatusCode = HttpStatusCode.Unauthorized; response.Content = new StringContent("Access denied"); response.Headers.WwwAuthenticate.Add(new AuthenticationHeaderValue("Basic", "realm=" + this.realm));  principal = null;  return false; } else { principal = new GenericPrincipal(new GenericIdentity(credentials[0]), new string[] {});  return true; } }  private string[] ExtractCredentials(HttpRequestMessage request) { if (request.Headers.Authorization != null && request.Headers.Authorization.Scheme.StartsWith("Basic")) { string encodedUserPass = request.Headers.Authorization.Parameter.Trim();  Encoding encoding = Encoding.GetEncoding("iso-8859-1"); string userPass = encoding.GetString(Convert.FromBase64String(encodedUserPass)); int separator = userPass.IndexOf(':');  string[] credentials = new string[2]; credentials[0] = userPass.Substring(0, separator); credentials[1] = userPass.Substring(separator + 1);  return credentials; }  return new string[] { }; }  private bool AuthenticateUser(string username, string password) { var usernameAndPassword = new UsernameAndPassword { Username = username, Password = password };  if (this.userValidation(usernameAndPassword)) { return true; }  return false; }} This interceptor receives in the constructor a callback in the form of a Func delegate for authenticating the user and the “realm”, which is required as part of the implementation. The rest is a general implementation of the basic authentication mechanism using standard http request and response messages. I also implemented another interceptor for authenticating a SAML token with WIF. public class SamlAuthenticationInterceptor : IAuthenticationInterceptor{ SecurityTokenHandlerCollection handlers = null;  public SamlAuthenticationInterceptor(SecurityTokenHandlerCollection handlers) { if (handlers == null) throw new ArgumentNullException("handlers");  this.handlers = handlers; }  public string Scheme { get { return "saml"; } }  public bool DoAuthentication(HttpRequestMessage request, HttpResponseMessage response, out IPrincipal principal) { SecurityToken token = ExtractCredentials(request);  if (token != null) { ClaimsIdentityCollection claims = handlers.ValidateToken(token);  principal = new ClaimsPrincipal(claims);  return true; } else { response.StatusCode = HttpStatusCode.Unauthorized; response.Content = new StringContent("Access denied");  principal = null;  return false; } }  private SecurityToken ExtractCredentials(HttpRequestMessage request) { if (request.Headers.Authorization != null && request.Headers.Authorization.Scheme == "saml") { XmlTextReader xmlReader = new XmlTextReader(new StringReader(request.Headers.Authorization.Parameter));  var col = SecurityTokenHandlerCollection.CreateDefaultSecurityTokenHandlerCollection(); SecurityToken token = col.ReadToken(xmlReader);  return token; }  return null; }}This implementation receives a “SecurityTokenHandlerCollection” instance as part of the constructor. This class is part of WIF, and basically represents a collection of token managers to know how to handle specific xml authentication tokens (SAML is one of them). I also created a set of extension methods for injecting these interceptors as part of a service route when the service is initialized. var basicAuthentication = new BasicAuthenticationInterceptor((u) => true, "ContactManager");var samlAuthentication = new SamlAuthenticationInterceptor(serviceConfiguration.SecurityTokenHandlers); // use MEF for providing instancesvar catalog = new AssemblyCatalog(typeof(Global).Assembly);var container = new CompositionContainer(catalog);var configuration = new ContactManagerConfiguration(container); RouteTable.Routes.AddServiceRoute<ContactResource>("contact", configuration, basicAuthentication, samlAuthentication);RouteTable.Routes.AddServiceRoute<ContactsResource>("contacts", configuration, basicAuthentication, samlAuthentication); In the code above, I am injecting the basic authentication and saml authentication interceptors in the “contact” and “contacts” resource implementations that come as samples in the code preview. I will use another post to discuss more in detail how the brokered authentication with SAML model works with this new WCF Http bits. The code is available to download in this location.

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  • Selectively Exposing Functionallity in .Net

    - by David V. Corbin
    Any developer should be aware of the principles of encapsulation, cross-tier isolation, and cross-functional separation of concerns. However, it seems the few take the time to consider the adage of "minimal yet complete"1 when developing the software. Consider the exposure of "business objects" to the user interface. Some common situations occur: Accessing a given element requires a compound set of calls that do not "make sense" to the User Interface. More information than absolutely required is exposed to the user interface It would be much cleaner if a custom interface was provided that exposed exactly (and only) the information that is required by the consumer. Achieving this using conventional techniques would require the creation (and maintenance!) of custom classes to filter and transpose the information into the ideal format. Determining the ROI on this approach can be very difficult to ascertain, and as a result it is often ignored completely. There is another approach, which is largely made practical by virtual of the Action and Func delegates. From a callers point of view, the following two samples can be used interchangeably:     interface ISomeInterface     {         void SampleMethod1(string param);         string SamepleMethod2(string param);     }       class ISomeInterface     {         public Action<string> SampleMethod1 {get; }         public Func<string,string> SamepleMethod2 {get; }     }   The capabilities this simple changes enable are significant (and remember it does not cange the syntax at the call site): The delegates can be initialized to directly call the proper method of any target class. The delegates can be dynamically updated based on the current state. The "interface" can NOT be cast to the concrete class (which often exposes more functionallity). This patterns By limiting the interface to the exact functionallity required, the reduced surface area will typically result in lower development, testing and maintenance costs. We are currently in the process of posting a project on CodePlex which illustrates this (and many other) techniques which have proven helpful in creating robust yet flexible solutions that are highly efficient2 and maintainable. This post will be updated as soon as the project is published. 1) Credit: Scott  Meyers, Effective C++, Addison-Wesley 1992 2) For those who read my previous post on performance it should be noted that the use of delegates is on the same order of magnitude (actually a tiny amount faster) as conventional interfaces.

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  • RIF PRD: Presentation syntax issues

    - by Charles Young
    Over Christmas I got to play a bit with the W3C RIF PRD and came across a few issues which I thought I would record for posterity. Specifically, I was working on a grammar for the presentation syntax using a GLR grammar parser tool (I was using the current CTP of ‘M’ (MGrammer) and Intellipad – I do so hope the MS guys don’t kill off M and Intellipad now they have dropped the other parts of SQL Server Modelling). I realise that the presentation syntax is non-normative and that any issues with it do not therefore compromise the standard. However, presentation syntax is useful in its own right, and it would be great to iron out any issues in a future revision of the standard. The main issues are actually not to do with the grammar at all, but rather with the ‘running example’ in the RIF PRD recommendation. I started with the code provided in Example 9.1. There are several discrepancies when compared with the EBNF rules documented in the standard. Broadly the problems can be categorised as follows: ·      Parenthesis mismatch – the wrong number of parentheses are used in various places. For example, in GoldRule, the RHS of the rule (the ‘Then’) is nested in the LHS (‘the If’). In NewCustomerAndWidgetRule, the RHS is orphaned from the LHS. Together with additional incorrect parenthesis, this leads to orphanage of UnknownStatusRule from the entire Document. ·      Invalid use of parenthesis in ‘Forall’ constructs. Parenthesis should not be used to enclose formulae. Removal of the invalid parenthesis gave me a feeling of inconsistency when comparing formulae in Forall to formulae in If. The use of parenthesis is not actually inconsistent in these two context, but in an If construct it ‘feels’ as if you are enclosing formulae in parenthesis in a LISP-like fashion. In reality, the parenthesis is simply being used to group subordinate syntax elements. The fact that an If construct can contain only a single formula as an immediate child adds to this feeling of inconsistency. ·      Invalid representation of compact URIs (CURIEs) in the context of Frame productions. In several places the URIs are not qualified with a namespace prefix (‘ex1:’). This conflicts with the definition of CURIEs in the RIF Datatypes and Built-Ins 1.0 document. Here are the productions: CURIE          ::= PNAME_LN                  | PNAME_NS PNAME_LN       ::= PNAME_NS PN_LOCAL PNAME_NS       ::= PN_PREFIX? ':' PN_LOCAL       ::= ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* PN_CHARS)? PN_CHARS       ::= PN_CHARS_U                  | '-' | [0-9] | #x00B7                  | [#x0300-#x036F] | [#x203F-#x2040] PN_CHARS_U     ::= PN_CHARS_BASE                  | '_' PN_CHARS_BASE ::= [A-Z] | [a-z] | [#x00C0-#x00D6] | [#x00D8-#x00F6]                  | [#x00F8-#x02FF] | [#x0370-#x037D] | [#x037F-#x1FFF]                  | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF]                  | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD]                  | [#x10000-#xEFFFF] PN_PREFIX      ::= PN_CHARS_BASE ((PN_CHARS|'.')* PN_CHARS)? The more I look at CURIEs, the more my head hurts! The RIF specification allows prefixes and colons without local names, which surprised me. However, the CURIE Syntax 1.0 working group note specifically states that this form is supported…and then promptly provides a syntactic definition that seems to preclude it! However, on (much) deeper inspection, it appears that ‘ex1:’ (for example) is allowed, but would really represent a ‘fragment’ of the ‘reference’, rather than a prefix! Ouch! This is so completely ambiguous that it surely calls into question the whole CURIE specification.   In any case, RIF does not allow local names without a prefix. ·      Missing ‘External’ specifiers for built-in functions and predicates.  The EBNF specification enforces this for terms within frames, but does not appear to enforce (what I believe is) the correct use of External on built-in predicates. In any case, the running example only specifies ‘External’ once on the predicate in UnknownStatusRule. External() is required in several other places. ·      The List used on the LHS of UnknownStatusRule is comma-delimited. This is not supported by the EBNF definition. Similarly, the argument list of pred:list-contains is illegally comma-delimited. ·      Unnecessary use of conjunction around a single formula in DiscountRule. This is strictly legal in the EBNF, but redundant.   All the above issues concern the presentation syntax used in the running example. There are a few minor issues with the grammar itself. Note that Michael Kiefer stated in his paper “Rule Interchange Format: The Framework” that: “The presentation syntax of RIF … is an abstract syntax and, as such, it omits certain details that might be important for unambiguous parsing.” ·      The grammar cannot differentiate unambiguously between strategies and priorities on groups. A processor is forced to resolve this by detecting the use of IRIs and integers. This could easily be fixed in the grammar.   ·      The grammar cannot unambiguously parse the ‘->’ operator in frames. Specifically, ‘-’ characters are allowed in PN_LOCAL names and hence a parser cannot determine if ‘status->’ is (‘status’ ‘->’) or (‘status-’ ‘>’).   One way to fix this is to amend the PN_LOCAL production as follows: PN_LOCAL ::= ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* ((PN_CHARS)-('-')))? However, unilaterally changing the definition of this production, which is defined in the SPARQL Query Language for RDF specification, makes me uncomfortable. ·      I assume that the presentation syntax is case-sensitive. I couldn’t find this stated anywhere in the documentation, but function/predicate names do appear to be documented as being case-sensitive. ·      The EBNF does not specify whitespace handling. A couple of productions (RULE and ACTION_BLOCK) are crafted to enforce the use of whitespace. This is not necessary. It seems inconsistent with the rest of the specification and can cause parsing issues. In addition, the Const production exhibits whitespaces issues. The intention may have been to disallow the use of whitespace around ‘^^’, but any direct implementation of the EBNF will probably allow whitespace between ‘^^’ and the SYMSPACE. Of course, I am being a little nit-picking about all this. On the whole, the EBNF translated very smoothly and directly to ‘M’ (MGrammar) and proved to be fairly complete. I have encountered far worse issues when translating other EBNF specifications into usable grammars.   I can’t imagine there would be any difficulty in implementing the same grammar in Antlr, COCO/R, gppg, XText, Bison, etc. A general observation, which repeats a point made above, is that the use of parenthesis in the presentation syntax can feel inconsistent and un-intuitive.   It isn’t actually inconsistent, but I think the presentation syntax could be improved by adopting braces, rather than parenthesis, to delimit subordinate syntax elements in a similar way to so many programming languages. The familiarity of braces would communicate the structure of the syntax more clearly to people like me.  If braces were adopted, parentheses could be retained around ‘var (frame | ‘new()’) constructs in action blocks. This use of parenthesis feels very LISP-like, and I think that this is my issue. It’s as if the presentation syntax represents the deformed love-child of LISP and C. In some places (specifically, action blocks), parenthesis is used in a LISP-like fashion. In other places it is used like braces in C. I find this quite confusing. Here is a corrected version of the running example (Example 9.1) in compliant presentation syntax: Document(    Prefix( ex1 <http://example.com/2009/prd2> )    (* ex1:CheckoutRuleset *)  Group rif:forwardChaining (     (* ex1:GoldRule *)    Group 10 (      Forall ?customer such that And(?customer # ex1:Customer                                     ?customer[ex1:status->"Silver"])        (Forall ?shoppingCart such that ?customer[ex1:shoppingCart->?shoppingCart]           (If Exists ?value (And(?shoppingCart[ex1:value->?value]                                  External(pred:numeric-greater-than-or-equal(?value 2000))))            Then Do(Modify(?customer[ex1:status->"Gold"])))))      (* ex1:DiscountRule *)    Group (      Forall ?customer such that ?customer # ex1:Customer        (If Or( ?customer[ex1:status->"Silver"]                ?customer[ex1:status->"Gold"])         Then Do ((?s ?customer[ex1:shoppingCart-> ?s])                  (?v ?s[ex1:value->?v])                  Modify(?s [ex1:value->External(func:numeric-multiply (?v 0.95))]))))      (* ex1:NewCustomerAndWidgetRule *)    Group (      Forall ?customer such that And(?customer # ex1:Customer                                     ?customer[ex1:status->"New"] )        (If Exists ?shoppingCart ?item                   (And(?customer[ex1:shoppingCart->?shoppingCart]                        ?shoppingCart[ex1:containsItem->?item]                        ?item # ex1:Widget ) )         Then Do( (?s ?customer[ex1:shoppingCart->?s])                  (?val ?s[ex1:value->?val])                  (?voucher ?customer[ex1:voucher->?voucher])                  Retract(?customer[ex1:voucher->?voucher])                  Retract(?voucher)                  Modify(?s[ex1:value->External(func:numeric-multiply(?val 0.90))]))))      (* ex1:UnknownStatusRule *)    Group (      Forall ?customer such that ?customer # ex1:Customer        (If Not(Exists ?status                       (And(?customer[ex1:status->?status]                            External(pred:list-contains(List("New" "Bronze" "Silver" "Gold") ?status)) )))         Then Do( Execute(act:print(External(func:concat("New customer: " ?customer))))                  Assert(?customer[ex1:status->"New"]))))  ) )   I hope that helps someone out there :-)

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  • Obtaining positional information in the IEnumerable Select extension method

    - by Kyle Burns
    This blog entry is intended to provide a narrow and brief look into a way to use the Select extension method that I had until recently overlooked. Every developer who is using IEnumerable extension methods to work with data has been exposed to the Select extension method, because it is a pretty critical piece of almost every query over a collection of objects.  The method is defined on type IEnumerable and takes as its argument a function that accepts an item from the collection and returns an object which will be an item within the returned collection.  This allows you to perform transformations on the source collection.  A somewhat contrived example would be the following code that transforms a collection of strings into a collection of anonymous objects: 1: var media = new[] {"book", "cd", "tape"}; 2: var transformed = media.Select( item => 3: { 4: Media = item 5: } ); This code transforms the array of strings into a collection of objects which each have a string property called Media. If every developer using the LINQ extension methods already knows this, why am I blogging about it?  I’m blogging about it because the method has another overload that I hadn’t seen before I needed it a few weeks back and I thought I would share a little about it with whoever happens upon my blog.  In the other overload, the function defined in the first overload as: 1: Func<TSource, TResult> is instead defined as: 1: Func<TSource, int, TResult>   The additional parameter is an integer representing the current element’s position in the enumerable sequence.  I used this information in what I thought was a pretty cool way to compare collections and I’ll probably blog about that sometime in the near future, but for now we’ll continue with the contrived example I’ve already started to keep things simple and show how this works.  The following code sample shows how the positional information could be used in an alternating color scenario.  I’m using a foreach loop because IEnumerable doesn’t have a ForEach extension, but many libraries do add the ForEach extension to IEnumerable so you can update the code if you’re using one of these libraries or have created your own. 1: var media = new[] {"book", "cd", "tape"}; 2: foreach (var result in media.Select( 3: (item, index) => 4: new { Item = item, Index = index })) 5: { 6: Console.ForegroundColor = result.Index % 2 == 0 7: ? ConsoleColor.Blue : ConsoleColor.Yellow; 8: Console.WriteLine(result.Item); 9: }

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  • How to remove the boundary effects arising due to zero padding in scipy/numpy fft?

    - by Omkar
    I have made a python code to smoothen a given signal using the Weierstrass transform, which is basically the convolution of a normalised gaussian with a signal. The code is as follows: #Importing relevant libraries from __future__ import division from scipy.signal import fftconvolve import numpy as np def smooth_func(sig, x, t= 0.002): N = len(x) x1 = x[-1] x0 = x[0] # defining a new array y which is symmetric around zero, to make the gaussian symmetric. y = np.linspace(-(x1-x0)/2, (x1-x0)/2, N) #gaussian centered around zero. gaus = np.exp(-y**(2)/t) #using fftconvolve to speed up the convolution; gaus.sum() is the normalization constant. return fftconvolve(sig, gaus/gaus.sum(), mode='same') If I run this code for say a step function, it smoothens the corner, but at the boundary it interprets another corner and smoothens that too, as a result giving unnecessary behaviour at the boundary. I explain this with a figure shown in the link below. Boundary effects This problem does not arise if we directly integrate to find convolution. Hence the problem is not in Weierstrass transform, and hence the problem is in the fftconvolve function of scipy. To understand why this problem arises we first need to understand the working of fftconvolve in scipy. The fftconvolve function basically uses the convolution theorem to speed up the computation. In short it says: convolution(int1,int2)=ifft(fft(int1)*fft(int2)) If we directly apply this theorem we dont get the desired result. To get the desired result we need to take the fft on a array double the size of max(int1,int2). But this leads to the undesired boundary effects. This is because in the fft code, if size(int) is greater than the size(over which to take fft) it zero pads the input and then takes the fft. This zero padding is exactly what is responsible for the undesired boundary effects. Can you suggest a way to remove this boundary effects? I have tried to remove it by a simple trick. After smoothening the function I am compairing the value of the smoothened signal with the original signal near the boundaries and if they dont match I replace the value of the smoothened func with the input signal at that point. It is as follows: i = 0 eps=1e-3 while abs(smooth[i]-sig[i])> eps: #compairing the signals on the left boundary smooth[i] = sig[i] i = i + 1 j = -1 while abs(smooth[j]-sig[j])> eps: # compairing on the right boundary. smooth[j] = sig[j] j = j - 1 There is a problem with this method, because of using an epsilon there are small jumps in the smoothened function, as shown below: jumps in the smooth func Can there be any changes made in the above method to solve this boundary problem?

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  • Lambda&rsquo;s for .NET made easy&hellip;

    - by mbcrump
    The purpose of my blog is to explain things for a beginner to intermediate c# programmer. I’ve seen several blog post that use lambda expressions always assuming the audience is familiar with them. The purpose of this post is to make them simple and easily understood. Let’s begin with a definition. A lambda expression is an anonymous function that can contain expressions and statements, and can be used to create delegates or expression tree types. So anonymous function… delegates or expression tree types? I don’t get it??? Confused yet?   Lets break this into a few definitions and jump right into the code. anonymous function – is an "inline" statement or expression that can be used wherever a delegate type is expected. delegate - is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method. The delegate method can be used like any other method, with parameters and a return value. Expression trees - represent code in a tree-like data structure, where each node is an expression, for example, a method call or a binary operation such as x < y.   Don’t worry if this still sounds confusing, lets jump right into the code with a simple 3 line program. We are going to use a Function Delegate (all you need to remember is that this delegate returns a value.) Lambda expressions are used most commonly with the Func and Action delegates, so you will see an example of both of these. Lambda Expression 3 lines. using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {             Func<int, int> myfunc = x => x *x;             Console.WriteLine(myfunc(6).ToString());             Console.ReadLine();         }       } } Is equivalent to Old way of doing it. using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {               Console.WriteLine(myFunc(6).ToString());             Console.ReadLine();         }            static int myFunc(int x)          {              return x * x;            }       } } In the example, there is a single parameter, x, and the expression is x*x. I’m going to stop here to make sure you are still with me. A lambda expression is an unnamed method written in place of a delegate instance. In other words, the compiler converts the lambda expression to either a : A delegate instance An expression tree All lambda have the following form: (parameters) => expression or statement block Now look back to the ones we have created. It should start to sink in. Don’t get stuck on the => form, use it as an identifier of a lambda. A Lamba expression can also be written in the following form: Lambda Expression. using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {             Func<int, int> myFunc = x =>             {                 return x * x;             };               Console.WriteLine(myFunc(6).ToString());             Console.ReadLine();         }       } } This form may be easier to read but consumes more space. Lets try an Action delegate – this delegate does not return a value. Action Delegate example. using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {             Action<string> myAction = (string x) => { Console.WriteLine(x); };             myAction("michael has made this so easy");                                   Console.ReadLine();         }       } } Lambdas can also capture outer variables (such as the example below) A lambda expression can reference the local variables and parameters of the method in which it’s defined. Outer variables referenced by a lambda expression are called captured variables. Capturing Outer Variables using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {             string mike = "Michael";             Action<string> myAction = (string x) => {                 Console.WriteLine("{0}{1}", mike, x);          };             myAction(" has made this so easy");                                   Console.ReadLine();         }       } } Lamba’s can also with a strongly typed list to loop through a collection.   Used w a strongly typed list. using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace ConsoleApplication7 {     class Program     {          static void Main(string[] args)         {             List<string> list = new List<string>() { "1", "2", "3", "4" };             list.ForEach(s => Console.WriteLine(s));             Console.ReadLine();         }       } } Outputs: 1 2 3 4 I think this will get you started with Lambda’s, as always consult the MSDN documentation for more information. Still confused? Hopefully you are not.

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  • Is 2 lines of push/pop code for each pre-draw-state too many?

    - by Griffin
    I'm trying to simplify vector graphics management in XNA; currently by incorporating state preservation. 2X lines of push/pop code for X states feels like too many, and it just feels wrong to have 2 lines of code that look identical except for one being push() and the other being pop(). The goal is to eradicate this repetitiveness,and I hoped to do so by creating an interface in which a client can give class/struct refs in which he wants restored after the rendering calls. Also note that many beginner-programmers will be using this, so forcing lambda expressions or other advanced C# features to be used in client code is not a good idea. I attempted to accomplish my goal by using Daniel Earwicker's Ptr class: public class Ptr<T> { Func<T> getter; Action<T> setter; public Ptr(Func<T> g, Action<T> s) { getter = g; setter = s; } public T Deref { get { return getter(); } set { setter(value); } } } an extension method: //doesn't work for structs since this is just syntatic sugar public static Ptr<T> GetPtr <T> (this T obj) { return new Ptr<T>( ()=> obj, v=> obj=v ); } and a Push Function: //returns a Pop Action for later calling public static Action Push <T> (ref T structure) where T: struct { T pushedValue = structure; //copies the struct data Ptr<T> p = structure.GetPtr(); return new Action( ()=> {p.Deref = pushedValue;} ); } However this doesn't work as stated in the code. How might I accomplish my goal? Example of code to be refactored: protected override void RenderLocally (GraphicsDevice device) { if (!(bool)isCompiled) {Compile();} //TODO: make sure state settings don't implicitly delete any buffers/resources RasterizerState oldRasterState = device.RasterizerState; DepthFormat oldFormat = device.PresentationParameters.DepthStencilFormat; DepthStencilState oldBufferState = device.DepthStencilState; { //Rendering code } device.RasterizerState = oldRasterState; device.DepthStencilState = oldBufferState; device.PresentationParameters.DepthStencilFormat = oldFormat; }

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  • IXRepository and test problems

    - by Ridermansb
    Recently had a doubt about how and where to test repository methods. Let the following situation: I have an interface IRepository like this: public interface IRepository<T> where T: class, IEntity { IQueryable<T> Query(Expression<Func<T, bool>> expression); // ... Omitted } And a generic implementation of IRepository public class Repository<T> : IRepository<T> where T : class, IEntity { public IQueryable<T> Query(Expression<Func<T, bool>> expression) { return All().Where(expression).AsQueryable(); } } This is an implementation base that can be used by any repository. It contains the basic implementation of my ORM. Some repositories have specific filters, in which case we will IEmployeeRepository with a specific filter: public interface IEmployeeRepository : IRepository<Employee> { IQueryable<Employee> GetInactiveEmployees(); } And the implementation of IEmployeeRepository: public class EmployeeRepository : Repository<Employee>, IEmployeeRepository // TODO: I have a dependency with ORM at this point in Repository<Employee>. How to solve? How to test the GetInactiveEmployees method { public IQueryable<Employee> GetInactiveEmployees() { return Query(p => p.Status != StatusEmployeeEnum.Active || p.StartDate < DateTime.Now); } } Questions Is right to inherit Repository<Employee>? The goal is to reuse code once all implementing IRepository already been made. If EmployeeRepository inherit only IEmployeeRepository, I have to literally copy and paste the code of Repository<T>. In our example, in EmployeeRepository : Repository<Employee> our Repository lies in our ORM layer. We have a dependency here with our ORM impossible to perform some unit test. How to create a unit test to ensure that the filter GetInactiveEmployees return all Employees in which the Status != Active and StartDate < DateTime.Now. I can not create a Fake/Mock of IEmployeeRepository because I would be testing? Need to test the actual implementation of GetInactiveEmployees. The complete code can be found on Github

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  • Interrupted system call during "hg convert"

    - by Aaron Digulla
    When I run "hg convert" to convert a Subversion repository to Mercurial, I get this error: fetching revision log for "/trunk" from 1538 to 0 run hg sink post-conversion action Traceback (most recent call last): File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 46, in _runcatch return _dispatch(ui, args) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 454, in _dispatch return runcommand(lui, repo, cmd, fullargs, ui, options, d) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 324, in runcommand ret = _runcommand(ui, options, cmd, d) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 505, in _runcommand return checkargs() File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 459, in checkargs return cmdfunc() File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 453, in <lambda> d = lambda: util.checksignature(func)(ui, *args, **cmdoptions) File "/usr/lib/pymodules/python2.6/mercurial/util.py", line 386, in check return func(*args, **kwargs) File "/usr/lib/pymodules/python2.6/hgext/convert/__init__.py", line 229, in convert return convcmd.convert(ui, src, dest, revmapfile, **opts) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 398, in convert c.convert(sortmode) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 312, in convert parents = self.walktree(heads) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 109, in walktree commit = self.cachecommit(n) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 267, in cachecommit commit = self.source.getcommit(rev) File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 433, in getcommit self._fetch_revisions(revnum, stop) File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 814, in _fetch_revisions for entry in stream: File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 122, in __iter__ entry = pickle.load(self._stdout) IOError: [Errno 4] Interrupted system call abort: Interrupted system call Apparently, it is possible to restart a read on EINTR but how would I do that with pickle.load()? Also I wonder where that signal comes from? I suspect it's SIGCHILD but shouldn't popen() handle that?

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  • Project Euler #15

    - by Aistina
    Hey everyone, Last night I was trying to solve challenge #15 from Project Euler: Starting in the top left corner of a 2×2 grid, there are 6 routes (without backtracking) to the bottom right corner. How many routes are there through a 20×20 grid? I figured this shouldn't be so hard, so I wrote a basic recursive function: const int gridSize = 20; // call with progress(0, 0) static int progress(int x, int y) { int i = 0; if (x < gridSize) i += progress(x + 1, y); if (y < gridSize) i += progress(x, y + 1); if (x == gridSize && y == gridSize) return 1; return i; } I verified that it worked for a smaller grids such as 2×2 or 3×3, and then set it to run for a 20×20 grid. Imagine my surprise when, 5 hours later, the program was still happily crunching the numbers, and only about 80% done (based on examining its current position/route in the grid). Clearly I'm going about this the wrong way. How would you solve this problem? I'm thinking it should be solved using an equation rather than a method like mine, but that's unfortunately not a strong side of mine. Update: I now have a working version. Basically it caches results obtained before when a n×m block still remains to be traversed. Here is the code along with some comments: // the size of our grid static int gridSize = 20; // the amount of paths available for a "NxM" block, e.g. "2x2" => 4 static Dictionary<string, long> pathsByBlock = new Dictionary<string, long>(); // calculate the surface of the block to the finish line static long calcsurface(long x, long y) { return (gridSize - x) * (gridSize - y); } // call using progress (0, 0) static long progress(long x, long y) { // first calculate the surface of the block remaining long surface = calcsurface(x, y); long i = 0; // zero surface means only 1 path remains // (we either go only right, or only down) if (surface == 0) return 1; // create a textual representation of the remaining // block, for use in the dictionary string block = (gridSize - x) + "x" + (gridSize - y); // if a same block has not been processed before if (!pathsByBlock.ContainsKey(block)) { // calculate it in the right direction if (x < gridSize) i += progress(x + 1, y); // and in the down direction if (y < gridSize) i += progress(x, y + 1); // and cache the result! pathsByBlock[block] = i; } // self-explanatory :) return pathsByBlock[block]; } Calling it 20 times, for grids with size 1×1 through 20×20 produces the following output: There are 2 paths in a 1 sized grid 0,0110006 seconds There are 6 paths in a 2 sized grid 0,0030002 seconds There are 20 paths in a 3 sized grid 0 seconds There are 70 paths in a 4 sized grid 0 seconds There are 252 paths in a 5 sized grid 0 seconds There are 924 paths in a 6 sized grid 0 seconds There are 3432 paths in a 7 sized grid 0 seconds There are 12870 paths in a 8 sized grid 0,001 seconds There are 48620 paths in a 9 sized grid 0,0010001 seconds There are 184756 paths in a 10 sized grid 0,001 seconds There are 705432 paths in a 11 sized grid 0 seconds There are 2704156 paths in a 12 sized grid 0 seconds There are 10400600 paths in a 13 sized grid 0,001 seconds There are 40116600 paths in a 14 sized grid 0 seconds There are 155117520 paths in a 15 sized grid 0 seconds There are 601080390 paths in a 16 sized grid 0,0010001 seconds There are 2333606220 paths in a 17 sized grid 0,001 seconds There are 9075135300 paths in a 18 sized grid 0,001 seconds There are 35345263800 paths in a 19 sized grid 0,001 seconds There are 137846528820 paths in a 20 sized grid 0,0010001 seconds 0,0390022 seconds in total I'm accepting danben's answer, because his helped me find this solution the most. But upvotes also to Tim Goodman and Agos :) Bonus update: After reading Eric Lippert's answer, I took another look and rewrote it somewhat. The basic idea is still the same but the caching part has been taken out and put in a separate function, like in Eric's example. The result is some much more elegant looking code. // the size of our grid const int gridSize = 20; // magic. static Func<A1, A2, R> Memoize<A1, A2, R>(this Func<A1, A2, R> f) { // Return a function which is f with caching. var dictionary = new Dictionary<string, R>(); return (A1 a1, A2 a2) => { R r; string key = a1 + "x" + a2; if (!dictionary.TryGetValue(key, out r)) { // not in cache yet r = f(a1, a2); dictionary.Add(key, r); } return r; }; } // calculate the surface of the block to the finish line static long calcsurface(long x, long y) { return (gridSize - x) * (gridSize - y); } // call using progress (0, 0) static Func<long, long, long> progress = ((Func<long, long, long>)((long x, long y) => { // first calculate the surface of the block remaining long surface = calcsurface(x, y); long i = 0; // zero surface means only 1 path remains // (we either go only right, or only down) if (surface == 0) return 1; // calculate it in the right direction if (x < gridSize) i += progress(x + 1, y); // and in the down direction if (y < gridSize) i += progress(x, y + 1); // self-explanatory :) return i; })).Memoize(); By the way, I couldn't think of a better way to use the two arguments as a key for the dictionary. I googled around a bit, and it seems this is a common solution. Oh well.

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  • New features of C# 4.0

    This article covers New features of C# 4.0. Article has been divided into below sections. Introduction. Dynamic Lookup. Named and Optional Arguments. Features for COM interop. Variance. Relationship with Visual Basic. Resources. Other interested readings… 22 New Features of Visual Studio 2008 for .NET Professionals 50 New Features of SQL Server 2008 IIS 7.0 New features Introduction It is now close to a year since Microsoft Visual C# 3.0 shipped as part of Visual Studio 2008. In the VS Managed Languages team we are hard at work on creating the next version of the language (with the unsurprising working title of C# 4.0), and this document is a first public description of the planned language features as we currently see them. Please be advised that all this is in early stages of production and is subject to change. Part of the reason for sharing our plans in public so early is precisely to get the kind of feedback that will cause us to improve the final product before it rolls out. Simultaneously with the publication of this whitepaper, a first public CTP (community technology preview) of Visual Studio 2010 is going out as a Virtual PC image for everyone to try. Please use it to play and experiment with the features, and let us know of any thoughts you have. We ask for your understanding and patience working with very early bits, where especially new or newly implemented features do not have the quality or stability of a final product. The aim of the CTP is not to give you a productive work environment but to give you the best possible impression of what we are working on for the next release. The CTP contains a number of walkthroughs, some of which highlight the new language features of C# 4.0. Those are excellent for getting a hands-on guided tour through the details of some common scenarios for the features. You may consider this whitepaper a companion document to these walkthroughs, complementing them with a focus on the overall language features and how they work, as opposed to the specifics of the concrete scenarios. C# 4.0 The major theme for C# 4.0 is dynamic programming. Increasingly, objects are “dynamic” in the sense that their structure and behavior is not captured by a static type, or at least not one that the compiler knows about when compiling your program. Some examples include a. objects from dynamic programming languages, such as Python or Ruby b. COM objects accessed through IDispatch c. ordinary .NET types accessed through reflection d. objects with changing structure, such as HTML DOM objects While C# remains a statically typed language, we aim to vastly improve the interaction with such objects. A secondary theme is co-evolution with Visual Basic. Going forward we will aim to maintain the individual character of each language, but at the same time important new features should be introduced in both languages at the same time. They should be differentiated more by style and feel than by feature set. The new features in C# 4.0 fall into four groups: Dynamic lookup Dynamic lookup allows you to write method, operator and indexer calls, property and field accesses, and even object invocations which bypass the C# static type checking and instead gets resolved at runtime. Named and optional parameters Parameters in C# can now be specified as optional by providing a default value for them in a member declaration. When the member is invoked, optional arguments can be omitted. Furthermore, any argument can be passed by parameter name instead of position. COM specific interop features Dynamic lookup as well as named and optional parameters both help making programming against COM less painful than today. On top of that, however, we are adding a number of other small features that further improve the interop experience. Variance It used to be that an IEnumerable<string> wasn’t an IEnumerable<object>. Now it is – C# embraces type safe “co-and contravariance” and common BCL types are updated to take advantage of that. Dynamic Lookup Dynamic lookup allows you a unified approach to invoking things dynamically. With dynamic lookup, when you have an object in your hand you do not need to worry about whether it comes from COM, IronPython, the HTML DOM or reflection; you just apply operations to it and leave it to the runtime to figure out what exactly those operations mean for that particular object. This affords you enormous flexibility, and can greatly simplify your code, but it does come with a significant drawback: Static typing is not maintained for these operations. A dynamic object is assumed at compile time to support any operation, and only at runtime will you get an error if it wasn’t so. Oftentimes this will be no loss, because the object wouldn’t have a static type anyway, in other cases it is a tradeoff between brevity and safety. In order to facilitate this tradeoff, it is a design goal of C# to allow you to opt in or opt out of dynamic behavior on every single call. The dynamic type C# 4.0 introduces a new static type called dynamic. When you have an object of type dynamic you can “do things to it” that are resolved only at runtime: dynamic d = GetDynamicObject(…); d.M(7); The C# compiler allows you to call a method with any name and any arguments on d because it is of type dynamic. At runtime the actual object that d refers to will be examined to determine what it means to “call M with an int” on it. The type dynamic can be thought of as a special version of the type object, which signals that the object can be used dynamically. It is easy to opt in or out of dynamic behavior: any object can be implicitly converted to dynamic, “suspending belief” until runtime. Conversely, there is an “assignment conversion” from dynamic to any other type, which allows implicit conversion in assignment-like constructs: dynamic d = 7; // implicit conversion int i = d; // assignment conversion Dynamic operations Not only method calls, but also field and property accesses, indexer and operator calls and even delegate invocations can be dispatched dynamically: dynamic d = GetDynamicObject(…); d.M(7); // calling methods d.f = d.P; // getting and settings fields and properties d[“one”] = d[“two”]; // getting and setting thorugh indexers int i = d + 3; // calling operators string s = d(5,7); // invoking as a delegate The role of the C# compiler here is simply to package up the necessary information about “what is being done to d”, so that the runtime can pick it up and determine what the exact meaning of it is given an actual object d. Think of it as deferring part of the compiler’s job to runtime. The result of any dynamic operation is itself of type dynamic. Runtime lookup At runtime a dynamic operation is dispatched according to the nature of its target object d: COM objects If d is a COM object, the operation is dispatched dynamically through COM IDispatch. This allows calling to COM types that don’t have a Primary Interop Assembly (PIA), and relying on COM features that don’t have a counterpart in C#, such as indexed properties and default properties. Dynamic objects If d implements the interface IDynamicObject d itself is asked to perform the operation. Thus by implementing IDynamicObject a type can completely redefine the meaning of dynamic operations. This is used intensively by dynamic languages such as IronPython and IronRuby to implement their own dynamic object models. It will also be used by APIs, e.g. by the HTML DOM to allow direct access to the object’s properties using property syntax. Plain objects Otherwise d is a standard .NET object, and the operation will be dispatched using reflection on its type and a C# “runtime binder” which implements C#’s lookup and overload resolution semantics at runtime. This is essentially a part of the C# compiler running as a runtime component to “finish the work” on dynamic operations that was deferred by the static compiler. Example Assume the following code: dynamic d1 = new Foo(); dynamic d2 = new Bar(); string s; d1.M(s, d2, 3, null); Because the receiver of the call to M is dynamic, the C# compiler does not try to resolve the meaning of the call. Instead it stashes away information for the runtime about the call. This information (often referred to as the “payload”) is essentially equivalent to: “Perform an instance method call of M with the following arguments: 1. a string 2. a dynamic 3. a literal int 3 4. a literal object null” At runtime, assume that the actual type Foo of d1 is not a COM type and does not implement IDynamicObject. In this case the C# runtime binder picks up to finish the overload resolution job based on runtime type information, proceeding as follows: 1. Reflection is used to obtain the actual runtime types of the two objects, d1 and d2, that did not have a static type (or rather had the static type dynamic). The result is Foo for d1 and Bar for d2. 2. Method lookup and overload resolution is performed on the type Foo with the call M(string,Bar,3,null) using ordinary C# semantics. 3. If the method is found it is invoked; otherwise a runtime exception is thrown. Overload resolution with dynamic arguments Even if the receiver of a method call is of a static type, overload resolution can still happen at runtime. This can happen if one or more of the arguments have the type dynamic: Foo foo = new Foo(); dynamic d = new Bar(); var result = foo.M(d); The C# runtime binder will choose between the statically known overloads of M on Foo, based on the runtime type of d, namely Bar. The result is again of type dynamic. The Dynamic Language Runtime An important component in the underlying implementation of dynamic lookup is the Dynamic Language Runtime (DLR), which is a new API in .NET 4.0. The DLR provides most of the infrastructure behind not only C# dynamic lookup but also the implementation of several dynamic programming languages on .NET, such as IronPython and IronRuby. Through this common infrastructure a high degree of interoperability is ensured, but just as importantly the DLR provides excellent caching mechanisms which serve to greatly enhance the efficiency of runtime dispatch. To the user of dynamic lookup in C#, the DLR is invisible except for the improved efficiency. However, if you want to implement your own dynamically dispatched objects, the IDynamicObject interface allows you to interoperate with the DLR and plug in your own behavior. This is a rather advanced task, which requires you to understand a good deal more about the inner workings of the DLR. For API writers, however, it can definitely be worth the trouble in order to vastly improve the usability of e.g. a library representing an inherently dynamic domain. Open issues There are a few limitations and things that might work differently than you would expect. · The DLR allows objects to be created from objects that represent classes. However, the current implementation of C# doesn’t have syntax to support this. · Dynamic lookup will not be able to find extension methods. Whether extension methods apply or not depends on the static context of the call (i.e. which using clauses occur), and this context information is not currently kept as part of the payload. · Anonymous functions (i.e. lambda expressions) cannot appear as arguments to a dynamic method call. The compiler cannot bind (i.e. “understand”) an anonymous function without knowing what type it is converted to. One consequence of these limitations is that you cannot easily use LINQ queries over dynamic objects: dynamic collection = …; var result = collection.Select(e => e + 5); If the Select method is an extension method, dynamic lookup will not find it. Even if it is an instance method, the above does not compile, because a lambda expression cannot be passed as an argument to a dynamic operation. There are no plans to address these limitations in C# 4.0. Named and Optional Arguments Named and optional parameters are really two distinct features, but are often useful together. Optional parameters allow you to omit arguments to member invocations, whereas named arguments is a way to provide an argument using the name of the corresponding parameter instead of relying on its position in the parameter list. Some APIs, most notably COM interfaces such as the Office automation APIs, are written specifically with named and optional parameters in mind. Up until now it has been very painful to call into these APIs from C#, with sometimes as many as thirty arguments having to be explicitly passed, most of which have reasonable default values and could be omitted. Even in APIs for .NET however you sometimes find yourself compelled to write many overloads of a method with different combinations of parameters, in order to provide maximum usability to the callers. Optional parameters are a useful alternative for these situations. Optional parameters A parameter is declared optional simply by providing a default value for it: public void M(int x, int y = 5, int z = 7); Here y and z are optional parameters and can be omitted in calls: M(1, 2, 3); // ordinary call of M M(1, 2); // omitting z – equivalent to M(1, 2, 7) M(1); // omitting both y and z – equivalent to M(1, 5, 7) Named and optional arguments C# 4.0 does not permit you to omit arguments between commas as in M(1,,3). This could lead to highly unreadable comma-counting code. Instead any argument can be passed by name. Thus if you want to omit only y from a call of M you can write: M(1, z: 3); // passing z by name or M(x: 1, z: 3); // passing both x and z by name or even M(z: 3, x: 1); // reversing the order of arguments All forms are equivalent, except that arguments are always evaluated in the order they appear, so in the last example the 3 is evaluated before the 1. Optional and named arguments can be used not only with methods but also with indexers and constructors. Overload resolution Named and optional arguments affect overload resolution, but the changes are relatively simple: A signature is applicable if all its parameters are either optional or have exactly one corresponding argument (by name or position) in the call which is convertible to the parameter type. Betterness rules on conversions are only applied for arguments that are explicitly given – omitted optional arguments are ignored for betterness purposes. If two signatures are equally good, one that does not omit optional parameters is preferred. M(string s, int i = 1); M(object o); M(int i, string s = “Hello”); M(int i); M(5); Given these overloads, we can see the working of the rules above. M(string,int) is not applicable because 5 doesn’t convert to string. M(int,string) is applicable because its second parameter is optional, and so, obviously are M(object) and M(int). M(int,string) and M(int) are both better than M(object) because the conversion from 5 to int is better than the conversion from 5 to object. Finally M(int) is better than M(int,string) because no optional arguments are omitted. Thus the method that gets called is M(int). Features for COM interop Dynamic lookup as well as named and optional parameters greatly improve the experience of interoperating with COM APIs such as the Office Automation APIs. In order to remove even more of the speed bumps, a couple of small COM-specific features are also added to C# 4.0. Dynamic import Many COM methods accept and return variant types, which are represented in the PIAs as object. In the vast majority of cases, a programmer calling these methods already knows the static type of a returned object from context, but explicitly has to perform a cast on the returned value to make use of that knowledge. These casts are so common that they constitute a major nuisance. In order to facilitate a smoother experience, you can now choose to import these COM APIs in such a way that variants are instead represented using the type dynamic. In other words, from your point of view, COM signatures now have occurrences of dynamic instead of object in them. This means that you can easily access members directly off a returned object, or you can assign it to a strongly typed local variable without having to cast. To illustrate, you can now say excel.Cells[1, 1].Value = "Hello"; instead of ((Excel.Range)excel.Cells[1, 1]).Value2 = "Hello"; and Excel.Range range = excel.Cells[1, 1]; instead of Excel.Range range = (Excel.Range)excel.Cells[1, 1]; Compiling without PIAs Primary Interop Assemblies are large .NET assemblies generated from COM interfaces to facilitate strongly typed interoperability. They provide great support at design time, where your experience of the interop is as good as if the types where really defined in .NET. However, at runtime these large assemblies can easily bloat your program, and also cause versioning issues because they are distributed independently of your application. The no-PIA feature allows you to continue to use PIAs at design time without having them around at runtime. Instead, the C# compiler will bake the small part of the PIA that a program actually uses directly into its assembly. At runtime the PIA does not have to be loaded. Omitting ref Because of a different programming model, many COM APIs contain a lot of reference parameters. Contrary to refs in C#, these are typically not meant to mutate a passed-in argument for the subsequent benefit of the caller, but are simply another way of passing value parameters. It therefore seems unreasonable that a C# programmer should have to create temporary variables for all such ref parameters and pass these by reference. Instead, specifically for COM methods, the C# compiler will allow you to pass arguments by value to such a method, and will automatically generate temporary variables to hold the passed-in values, subsequently discarding these when the call returns. In this way the caller sees value semantics, and will not experience any side effects, but the called method still gets a reference. Open issues A few COM interface features still are not surfaced in C#. Most notably these include indexed properties and default properties. As mentioned above these will be respected if you access COM dynamically, but statically typed C# code will still not recognize them. There are currently no plans to address these remaining speed bumps in C# 4.0. Variance An aspect of generics that often comes across as surprising is that the following is illegal: IList<string> strings = new List<string>(); IList<object> objects = strings; The second assignment is disallowed because strings does not have the same element type as objects. There is a perfectly good reason for this. If it were allowed you could write: objects[0] = 5; string s = strings[0]; Allowing an int to be inserted into a list of strings and subsequently extracted as a string. This would be a breach of type safety. However, there are certain interfaces where the above cannot occur, notably where there is no way to insert an object into the collection. Such an interface is IEnumerable<T>. If instead you say: IEnumerable<object> objects = strings; There is no way we can put the wrong kind of thing into strings through objects, because objects doesn’t have a method that takes an element in. Variance is about allowing assignments such as this in cases where it is safe. The result is that a lot of situations that were previously surprising now just work. Covariance In .NET 4.0 the IEnumerable<T> interface will be declared in the following way: public interface IEnumerable<out T> : IEnumerable { IEnumerator<T> GetEnumerator(); } public interface IEnumerator<out T> : IEnumerator { bool MoveNext(); T Current { get; } } The “out” in these declarations signifies that the T can only occur in output position in the interface – the compiler will complain otherwise. In return for this restriction, the interface becomes “covariant” in T, which means that an IEnumerable<A> is considered an IEnumerable<B> if A has a reference conversion to B. As a result, any sequence of strings is also e.g. a sequence of objects. This is useful e.g. in many LINQ methods. Using the declarations above: var result = strings.Union(objects); // succeeds with an IEnumerable<object> This would previously have been disallowed, and you would have had to to some cumbersome wrapping to get the two sequences to have the same element type. Contravariance Type parameters can also have an “in” modifier, restricting them to occur only in input positions. An example is IComparer<T>: public interface IComparer<in T> { public int Compare(T left, T right); } The somewhat baffling result is that an IComparer<object> can in fact be considered an IComparer<string>! It makes sense when you think about it: If a comparer can compare any two objects, it can certainly also compare two strings. This property is referred to as contravariance. A generic type can have both in and out modifiers on its type parameters, as is the case with the Func<…> delegate types: public delegate TResult Func<in TArg, out TResult>(TArg arg); Obviously the argument only ever comes in, and the result only ever comes out. Therefore a Func<object,string> can in fact be used as a Func<string,object>. Limitations Variant type parameters can only be declared on interfaces and delegate types, due to a restriction in the CLR. Variance only applies when there is a reference conversion between the type arguments. For instance, an IEnumerable<int> is not an IEnumerable<object> because the conversion from int to object is a boxing conversion, not a reference conversion. Also please note that the CTP does not contain the new versions of the .NET types mentioned above. In order to experiment with variance you have to declare your own variant interfaces and delegate types. COM Example Here is a larger Office automation example that shows many of the new C# features in action. using System; using System.Diagnostics; using System.Linq; using Excel = Microsoft.Office.Interop.Excel; using Word = Microsoft.Office.Interop.Word; class Program { static void Main(string[] args) { var excel = new Excel.Application(); excel.Visible = true; excel.Workbooks.Add(); // optional arguments omitted excel.Cells[1, 1].Value = "Process Name"; // no casts; Value dynamically excel.Cells[1, 2].Value = "Memory Usage"; // accessed var processes = Process.GetProcesses() .OrderByDescending(p =&gt; p.WorkingSet) .Take(10); int i = 2; foreach (var p in processes) { excel.Cells[i, 1].Value = p.ProcessName; // no casts excel.Cells[i, 2].Value = p.WorkingSet; // no casts i++; } Excel.Range range = excel.Cells[1, 1]; // no casts Excel.Chart chart = excel.ActiveWorkbook.Charts. Add(After: excel.ActiveSheet); // named and optional arguments chart.ChartWizard( Source: range.CurrentRegion, Title: "Memory Usage in " + Environment.MachineName); //named+optional chart.ChartStyle = 45; chart.CopyPicture(Excel.XlPictureAppearance.xlScreen, Excel.XlCopyPictureFormat.xlBitmap, Excel.XlPictureAppearance.xlScreen); var word = new Word.Application(); word.Visible = true; word.Documents.Add(); // optional arguments word.Selection.Paste(); } } The code is much more terse and readable than the C# 3.0 counterpart. Note especially how the Value property is accessed dynamically. This is actually an indexed property, i.e. a property that takes an argument; something which C# does not understand. However the argument is optional. Since the access is dynamic, it goes through the runtime COM binder which knows to substitute the default value and call the indexed property. Thus, dynamic COM allows you to avoid accesses to the puzzling Value2 property of Excel ranges. Relationship with Visual Basic A number of the features introduced to C# 4.0 already exist or will be introduced in some form or other in Visual Basic: · Late binding in VB is similar in many ways to dynamic lookup in C#, and can be expected to make more use of the DLR in the future, leading to further parity with C#. · Named and optional arguments have been part of Visual Basic for a long time, and the C# version of the feature is explicitly engineered with maximal VB interoperability in mind. · NoPIA and variance are both being introduced to VB and C# at the same time. VB in turn is adding a number of features that have hitherto been a mainstay of C#. As a result future versions of C# and VB will have much better feature parity, for the benefit of everyone. Resources All available resources concerning C# 4.0 can be accessed through the C# Dev Center. Specifically, this white paper and other resources can be found at the Code Gallery site. Enjoy! span.fullpost {display:none;}

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  • Lightning talk: Coderetreat

    - by Michael Williamson
    In the spirit of trying to encourage more deliberate practice amongst coders in Red Gate, Lauri Pesonen had the idea of running a coderetreat in Red Gate. Lauri and I ran the first one a few weeks ago: given that neither of us hadn’t even been to a coderetreat before, let alone run one, I think it turned out quite well. The participants gave positive feedback, saying that they enjoyed the day, wrote some thought-provoking code and would do it again. Sam Blackburn was one of the attendees, and gave a lightning talk to the other developers in one of our regular lightning talk sessions: In case you can’t watch the video, I’ve transcribed the talk below, although I’d recommend watching the video if you can — I didn’t have much time to do the transcribing! So, what is a coderetreat? So it’s not just something in Red Gate, there’s a website and everything, although it’s not a very big website. It calls itself a community network. The basic ideas behind coderetreat are: you’ve got one day, and you split it into one hour sections. You spend three quarters of that coding, and do a little retrospective at the end. You’re supposed to start fresh each, we were told to delete our code after every session. We were in pairs, swapping after each session, and we did the same task every time. In fact, Conway’s Game of Life is the only task mentioned anywhere that I find for coderetreat. So I don’t know what we’ll do next time, or if we’re meant to do the same thing again. There are some guiding principles which felt to us like restrictions, that you have to code in crazy ways to encourage better code. Final thing is that it’s supposed to be free for outsiders to join. It’s meant to be a kind of networking thing, where you link up with people from other companies. We had a pilot day with Michael and Lauri. Since it was basically the first time any of us had done anything like this, everybody was from Red Gate. We didn’t chat to anybody else for the initial one. The task was Conway’s Game of Life, which most of you have probably heard of it, all but one of us knew about it when did the coderetreat. I won’t got into the details of what it is, but it felt like the right size of task, basically one or two groups actually produced something working by the end of the day, and of course that doesn’t mean it’s necessarily a day’s work to produce that because we were starting again every hour. The task really drives you more than trying to create good code, I found. It was really tempting to try and get it working rather than stick to the rules. But it’s really good to stop and try again because there are so many what-ifs when you’ve finished writing something, “what if I’d done it this way?”. You can answer all those questions at a coderetreat because it’s not about getting a product out the door, it’s about learning and playing with ideas. So we had all these different practices we were trying. I’ll try and go through most of these. Single responsibility is this idea that everything should do just one thing. It was the very first session, we were still trying to figure out how do you go about the Game of Life? So by the end of forty-five minutes hadn’t produced very much for that first session. We were still thinking, “Do we start with a board, how do we represent all these squares? It can be infinitely big, help, this is getting really difficult!”. So, most of us didn’t really get anywhere on the first one. Although it was interesting that some people started with the board, one group started with the FateDecider class that decides whether things live or die. A sort of god class, but in a good way. They managed to implement all of the rules without even defining how the squares were arranged or anything like that. Another thing we tried was TDD (test-driven development). I’m sure most of you know what TDD is: Watch a test, watch it fail for the right reason Write code to pass the test, watch it pass Refactor, check the test still passes Repeat! It basically worked, we were able to produce code, but we often found the tests defined the direction that code went, which is obviously the idea of TDD. But you tend to find that by the time you’ve even written your first assertion, which is supposed to be the very first thing you write, because you write your tests backwards from the assertions back to the initial conditions, you’ve already constrained the logic of the code in some way by the time you’ve done that. You then get to this situation of, “Well, we actually want to go in a slightly different direction. Can we do this?”. Can we write tests that don’t constrain the architecture? Wrapping up all primitives: it’s kind of turtles all the way down. We had a Size, which has a Width and Height, which both derive from Dimension. You’ve got pages of code before you’ve even done anything. No getters and setters (use tell don’t ask instead): mocks and stubs for tests are required if you want to assert that your results are what you think they should be. You can’t just check the internal state of the code. And people found that really challenging and it made them think in a different way which I think is really good. Not having mutable state: that was kind of confusing because we weren’t quite sure what fitted within that rule and what didn’t, and I think we were trying too hard to follow the rule rather than the guideline. No if-statements: supposed to use polymorphism instead, but polymorphism still requires a factory with conditional behaviour. We did something really crazy to get around this: public T If(bool condition, Func<T> left, Func<T> right) { var dict = new Dictionary<bool, Func<T>> {{true, left}, {false, right}}; return dict[condition].Invoke(); } That is not really polymorphism, is it? For-loops: you can always replace a for-loop with recursion, but it doesn’t tend to make it any more readable unless it’s the kind of task that really lends itself to that. So it was interesting, it was good practice, but it wouldn’t make it easier it’s the kind of tree-structure algorithm where that would help. Having a limit on the number of levels of indentation: again, I think it does produce very nice, clean code, but it wasn’t actually a challenge because you just extract methods. That’s quite a useful thing because you can apply that to real code and say, “Okay, should this method really be going crazy like this?” No talking: we hated that. It’s like there’s two of you at a computer, and one of you is doing the typing, what does the other guy do if they’re not allowed to talk. The answer is TDD ping-pong – one person writes the tests, and then the other person writes the code to pass the test. And that creates communication without actually having to have discussion about things which is kind of cool. No code comments: just makes no difference to anything. It’s a forty-five minute exercise, so what are you going to put comments in code for? Finally, this is my fault. I discovered an entertaining way of doing the calculation that was kind of cool (using convolutions over the state of the board). Unfortunately, it turns out to be really hard to implement in C#, so didn’t even manage to work out how to do that convolution in C#. It’s trivial in some high-level languages, but you need something matrix-orientated for it to really work. That’s most of it, really. The thoughts that people went away with: we put down our answers to questions like “What have you learnt?” and “What surprised you?”, “How are you going to do things differently?”, and most people said redoing the problem is really, really good for understanding it properly. People hate having a massive legacy codebase that they can’t change, so being able to attack something three different ways in an environment where the end-product isn’t important: that’s something people really enjoyed. Pair-programming: also people said that they wanted to do more of that, especially with TDD ping-pong, where you write the test and somebody else writes the code. Various people thought different things about immutables, but most people thought they were good, they promote functional programming. And TDD people found really hard. “Tell, don’t ask” people found really, really hard and really, really, really hard to do well. And the recursion just made things trickier to debug. But most people agreed that coderetreats are really cool, and we should do more of them.

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  • Enumerable Interleave Extension Method

    - by João Angelo
    A recent stackoverflow question, which I didn’t bookmark and now I’m unable to find, inspired me to implement an extension method for Enumerable that allows to insert a constant element between each pair of elements in a sequence. Kind of what String.Join does for strings, but maintaining an enumerable as the return value. Having done the single element part I got a bit carried away and ended up expanding it adding overloads to support interleaving elements of another sequence and support for a predicate to control when interleaving takes place. I have to confess that I did this for fun and now I can’t think of any real usage scenario, nonetheless, it may prove useful for someone. First a simple example: var target = new string[] { "(", ")", "(", ")" }; var result = target.Interleave(".", (f, s) => f == "("); // Prints: (.)(.) Console.WriteLine(String.Join(string.Empty, result)); And now the untested but documented implementation: using System; using System.Collections; using System.Collections.Generic; using System.Linq; public static class EnumerableExtensions { /// <summary> /// Iterates infinitely over a constant element. /// </summary> /// <typeparam name="T"> /// The type of element in the sequence. /// </typeparam> private class InfiniteSequence<T> : IEnumerable<T>, IEnumerator<T> { public InfiniteSequence(T element) { this.Element = element; } public T Element { get; private set; } public IEnumerator<T> GetEnumerator() { return this; } IEnumerator IEnumerable.GetEnumerator() { return this; } T IEnumerator<T>.Current { get { return this.Element; } } void IDisposable.Dispose() { } object IEnumerator.Current { get { return this.Element; } } bool IEnumerator.MoveNext() { return true; } void IEnumerator.Reset() { } } /// <summary> /// Interleaves the specified <paramref name="element"/> between each pair of elements in the <paramref name="target"/> sequence. /// </summary> /// <typeparam name="T"> /// The type of elements in the sequence. /// </typeparam> /// <param name="target"> /// The target sequence to be interleaved. /// </param> /// <param name="element"> /// The element used to perform the interleave operation. /// </param> /// <exception cref="ArgumentNullException"> /// <paramref name="target"/> or <paramref name="element"/> is a null reference. /// </exception> /// <returns> /// The <paramref name="target"/> sequence interleaved with the specified <paramref name="element"/>. /// </returns> public static IEnumerable<T> Interleave<T>( this IEnumerable<T> target, T element) { if (target == null) throw new ArgumentNullException("target"); if (element == null) throw new ArgumentNullException("element"); return InterleaveInternal(target, new InfiniteSequence<T>(element), (f, s) => true); } /// <summary> /// Interleaves the specified <paramref name="element"/> between each pair of elements in the <paramref name="target"/> sequence. /// </summary> /// <remarks> /// The interleave operation is interrupted as soon as the <paramref name="target"/> sequence is exhausted; If the number of <paramref name="elements"/> to be interleaved are not enough to completely interleave the <paramref name="target"/> sequence then the remainder of the sequence is returned without being interleaved. /// </remarks> /// <typeparam name="T"> /// The type of elements in the sequence. /// </typeparam> /// <param name="target"> /// The target sequence to be interleaved. /// </param> /// <param name="elements"> /// The elements used to perform the interleave operation. /// </param> /// <exception cref="ArgumentNullException"> /// <paramref name="target"/> or <paramref name="element"/> is a null reference. /// </exception> /// <returns> /// The <paramref name="target"/> sequence interleaved with the specified <paramref name="elements"/>. /// </returns> public static IEnumerable<T> Interleave<T>( this IEnumerable<T> target, IEnumerable<T> elements) { if (target == null) throw new ArgumentNullException("target"); if (elements == null) throw new ArgumentNullException("elements"); return InterleaveInternal(target, elements, (f, s) => true); } /// <summary> /// Interleaves the specified <paramref name="element"/> between each pair of elements in the <paramref name="target"/> sequence that satisfy <paramref name="predicate"/>. /// </summary> /// <typeparam name="T"> /// The type of elements in the sequence. /// </typeparam> /// <param name="target"> /// The target sequence to be interleaved. /// </param> /// <param name="element"> /// The element used to perform the interleave operation. /// </param> /// <param name="predicate"> /// A predicate used to assert if interleaving should occur between two target elements. /// </param> /// <exception cref="ArgumentNullException"> /// <paramref name="target"/> or <paramref name="element"/> or <paramref name="predicate"/> is a null reference. /// </exception> /// <returns> /// The <paramref name="target"/> sequence interleaved with the specified <paramref name="element"/>. /// </returns> public static IEnumerable<T> Interleave<T>( this IEnumerable<T> target, T element, Func<T, T, bool> predicate) { if (target == null) throw new ArgumentNullException("target"); if (element == null) throw new ArgumentNullException("element"); if (predicate == null) throw new ArgumentNullException("predicate"); return InterleaveInternal(target, new InfiniteSequence<T>(element), predicate); } /// <summary> /// Interleaves the specified <paramref name="element"/> between each pair of elements in the <paramref name="target"/> sequence that satisfy <paramref name="predicate"/>. /// </summary> /// <remarks> /// The interleave operation is interrupted as soon as the <paramref name="target"/> sequence is exhausted; If the number of <paramref name="elements"/> to be interleaved are not enough to completely interleave the <paramref name="target"/> sequence then the remainder of the sequence is returned without being interleaved. /// </remarks> /// <typeparam name="T"> /// The type of elements in the sequence. /// </typeparam> /// <param name="target"> /// The target sequence to be interleaved. /// </param> /// <param name="elements"> /// The elements used to perform the interleave operation. /// </param> /// <param name="predicate"> /// A predicate used to assert if interleaving should occur between two target elements. /// </param> /// <exception cref="ArgumentNullException"> /// <paramref name="target"/> or <paramref name="element"/> or <paramref name="predicate"/> is a null reference. /// </exception> /// <returns> /// The <paramref name="target"/> sequence interleaved with the specified <paramref name="elements"/>. /// </returns> public static IEnumerable<T> Interleave<T>( this IEnumerable<T> target, IEnumerable<T> elements, Func<T, T, bool> predicate) { if (target == null) throw new ArgumentNullException("target"); if (elements == null) throw new ArgumentNullException("elements"); if (predicate == null) throw new ArgumentNullException("predicate"); return InterleaveInternal(target, elements, predicate); } private static IEnumerable<T> InterleaveInternal<T>( this IEnumerable<T> target, IEnumerable<T> elements, Func<T, T, bool> predicate) { var targetEnumerator = target.GetEnumerator(); if (targetEnumerator.MoveNext()) { var elementsEnumerator = elements.GetEnumerator(); while (true) { T first = targetEnumerator.Current; yield return first; if (!targetEnumerator.MoveNext()) yield break; T second = targetEnumerator.Current; bool interleave = true && predicate(first, second) && elementsEnumerator.MoveNext(); if (interleave) yield return elementsEnumerator.Current; } } } }

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  • Changes to the LINQ-to-StreamInsight Dialect

    - by Roman Schindlauer
    In previous versions of StreamInsight (1.0 through 2.0), CepStream<> represents temporal streams of many varieties: Streams with ‘open’ inputs (e.g., those defined and composed over CepStream<T>.Create(string streamName) Streams with ‘partially bound’ inputs (e.g., those defined and composed over CepStream<T>.Create(Type adapterFactory, …)) Streams with fully bound inputs (e.g., those defined and composed over To*Stream – sequences or DQC) The stream may be embedded (where Server.Create is used) The stream may be remote (where Server.Connect is used) When adding support for new programming primitives in StreamInsight 2.1, we faced a choice: Add a fourth variety (use CepStream<> to represent streams that are bound the new programming model constructs), or introduce a separate type that represents temporal streams in the new user model. We opted for the latter. Introducing a new type has the effect of reducing the number of (confusing) runtime failures due to inappropriate uses of CepStream<> instances in the incorrect context. The new types are: IStreamable<>, which logically represents a temporal stream. IQStreamable<> : IStreamable<>, which represents a queryable temporal stream. Its relationship to IStreamable<> is analogous to the relationship of IQueryable<> to IEnumerable<>. The developer can compose temporal queries over remote stream sources using this type. The syntax of temporal queries composed over IQStreamable<> is mostly consistent with the syntax of our existing CepStream<>-based LINQ provider. However, we have taken the opportunity to refine certain aspects of the language surface. Differences are outlined below. Because 2.1 introduces new types to represent temporal queries, the changes outlined in this post do no impact existing StreamInsight applications using the existing types! SelectMany StreamInsight does not support the SelectMany operator in its usual form (which is analogous to SQL’s “CROSS APPLY” operator): static IEnumerable<R> SelectMany<T, R>(this IEnumerable<T> source, Func<T, IEnumerable<R>> collectionSelector) It instead uses SelectMany as a convenient syntactic representation of an inner join. The parameter to the selector function is thus unavailable. Because the parameter isn’t supported, its type in StreamInsight 1.0 – 2.0 wasn’t carefully scrutinized. Unfortunately, the type chosen for the parameter is nonsensical to LINQ programmers: static CepStream<R> SelectMany<T, R>(this CepStream<T> source, Expression<Func<CepStream<T>, CepStream<R>>> streamSelector) Using Unit as the type for the parameter accurately reflects the StreamInsight’s capabilities: static IQStreamable<R> SelectMany<T, R>(this IQStreamable<T> source, Expression<Func<Unit, IQStreamable<R>>> streamSelector) For queries that succeed – that is, queries that do not reference the stream selector parameter – there is no difference between the code written for the two overloads: from x in xs from y in ys select f(x, y) Top-K The Take operator used in StreamInsight causes confusion for LINQ programmers because it is applied to the (unbounded) stream rather than the (bounded) window, suggesting that the query as a whole will return k rows: (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) The use of SelectMany is also unfortunate in this context because it implies the availability of the window parameter within the remainder of the comprehension. The following compiles but fails at runtime: (from win in xs.SnapshotWindow() from x in win orderby x.A select win).Take(k) The Take operator in 2.1 is applied to the window rather than the stream: Before After (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) from win in xs.SnapshotWindow() from b in     (from x in win     orderby x.A     select x.B).Take(k) select b Multicast We are introducing an explicit multicast operator in order to preserve expression identity, which is important given the semantics about moving code to and from StreamInsight. This also better matches existing LINQ dialects, such as Reactive. This pattern enables expressing multicasting in two ways: Implicit Explicit var ys = from x in xs          where x.A > 1          select x; var zs = from y1 in ys          from y2 in ys.ShiftEventTime(_ => TimeSpan.FromSeconds(1))          select y1 + y2; var ys = from x in xs          where x.A > 1          select x; var zs = ys.Multicast(ys1 =>     from y1 in ys1     from y2 in ys1.ShiftEventTime(_ => TimeSpan.FromSeconds(1))     select y1 + y2; Notice the product translates an expression using implicit multicast into an expression using the explicit multicast operator. The user does not see this translation. Default window policies Only default window policies are supported in the new surface. Other policies can be simulated by using AlterEventLifetime. Before After xs.SnapshotWindow(     WindowInputPolicy.ClipToWindow,     SnapshotWindowInputPolicy.Clip) xs.SnapshotWindow() xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.PointAlignToWindowEnd) xs.TumblingWindow(     TimeSpan.FromSeconds(1)) xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.ClipToWindowEnd) Not supported … LeftAntiJoin Representation of LASJ as a correlated sub-query in the LINQ surface is problematic as the StreamInsight engine does not support correlated sub-queries (see discussion of SelectMany). The current syntax requires the introduction of an otherwise unsupported ‘IsEmpty()’ operator. As a result, the pattern is not discoverable and implies capabilities not present in the server. The direct representation of LASJ is used instead: Before After from x in xs where     (from y in ys     where x.A > y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, (x, y) => x.A > y.B) from x in xs where     (from y in ys     where x.A == y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, x => x.A, y => y.B) ApplyWithUnion The ApplyWithUnion methods have been deprecated since their signatures are redundant given the standard SelectMany overloads: Before After xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count()) xs.GroupBy(x => x.A).SelectMany(     gs =>     from win in gs.SnapshotWindow()     select win.Count()) xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count(), r => new { r.Key, Count = r.Payload }) from x in xs group x by x.A into gs from win in gs.SnapshotWindow() select new { gs.Key, Count = win.Count() } Alternate UDO syntax The representation of UDOs in the StreamInsight LINQ dialect confuses cardinalities. Based on the semantics of user-defined operators in StreamInsight, one would expect to construct queries in the following form: from win in xs.SnapshotWindow() from y in MyUdo(win) select y Instead, the UDO proxy method is referenced within a projection, and the (many) results returned by the user code are automatically flattened into a stream: from win in xs.SnapshotWindow() select MyUdo(win) The “many-or-one” confusion is exemplified by the following example that compiles but fails at runtime: from win in xs.SnapshotWindow() select MyUdo(win) + win.Count() The above query must fail because the UDO is in fact returning many values per window while the count aggregate is returning one. Original syntax New alternate syntax from win in xs.SnapshotWindow() select win.UdoProxy(1) from win in xs.SnapshotWindow() from y in win.UserDefinedOperator(() => new Udo(1)) select y -or- from win in xs.SnapshotWindow() from y in win.UdoMacro(1) select y Notice that this formulation also sidesteps the dynamic type pitfalls of the existing “proxy method” approach to UDOs, in which the type of the UDO implementation (TInput, TOuput) and the type of its constructor arguments (TConfig) need to align in a precise and non-obvious way with the argument and return types for the corresponding proxy method. UDSO syntax UDSO currently leverages the DataContractSerializer to clone initial state for logical instances of the user operator. Initial state will instead be described by an expression in the new LINQ surface. Before After xs.Scan(new Udso()) xs.Scan(() => new Udso()) Name changes ShiftEventTime => AlterEventStartTime: The alter event lifetime overload taking a new start time value has been renamed. CountByStartTimeWindow => CountWindow

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  • StreamInsight 2.1, meet LINQ

    - by Roman Schindlauer
    Someone recently called LINQ “magic” in my hearing. I leapt to LINQ’s defense immediately. Turns out some people don’t realize “magic” is can be a pejorative term. I thought LINQ needed demystification. Here’s your best demystification resource: http://blogs.msdn.com/b/mattwar/archive/2008/11/18/linq-links.aspx. I won’t repeat much of what Matt Warren says in his excellent series, but will talk about some core ideas and how they affect the 2.1 release of StreamInsight. Let’s tell the story of a LINQ query. Compile time It begins with some code: IQueryable<Product> products = ...; var query = from p in products             where p.Name == "Widget"             select p.ProductID; foreach (int id in query) {     ... When the code is compiled, the C# compiler (among other things) de-sugars the query expression (see C# spec section 7.16): ... var query = products.Where(p => p.Name == "Widget").Select(p => p.ProductID); ... Overload resolution subsequently binds the Queryable.Where<Product> and Queryable.Select<Product, int> extension methods (see C# spec sections 7.5 and 7.6.5). After overload resolution, the compiler knows something interesting about the anonymous functions (lambda syntax) in the de-sugared code: they must be converted to expression trees, i.e.,“an object structure that represents the structure of the anonymous function itself” (see C# spec section 6.5). The conversion is equivalent to the following rewrite: ... var prm1 = Expression.Parameter(typeof(Product), "p"); var prm2 = Expression.Parameter(typeof(Product), "p"); var query = Queryable.Select<Product, int>(     Queryable.Where<Product>(         products,         Expression.Lambda<Func<Product, bool>>(Expression.Property(prm1, "Name"), prm1)),         Expression.Lambda<Func<Product, int>>(Expression.Property(prm2, "ProductID"), prm2)); ... If the “products” expression had type IEnumerable<Product>, the compiler would have chosen the Enumerable.Where and Enumerable.Select extension methods instead, in which case the anonymous functions would have been converted to delegates. At this point, we’ve reduced the LINQ query to familiar code that will compile in C# 2.0. (Note that I’m using C# snippets to illustrate transformations that occur in the compiler, not to suggest a viable compiler design!) Runtime When the above program is executed, the Queryable.Where method is invoked. It takes two arguments. The first is an IQueryable<> instance that exposes an Expression property and a Provider property. The second is an expression tree. The Queryable.Where method implementation looks something like this: public static IQueryable<T> Where<T>(this IQueryable<T> source, Expression<Func<T, bool>> predicate) {     return source.Provider.CreateQuery<T>(     Expression.Call(this method, source.Expression, Expression.Quote(predicate))); } Notice that the method is really just composing a new expression tree that calls itself with arguments derived from the source and predicate arguments. Also notice that the query object returned from the method is associated with the same provider as the source query. By invoking operator methods, we’re constructing an expression tree that describes a query. Interestingly, the compiler and operator methods are colluding to construct a query expression tree. The important takeaway is that expression trees are built in one of two ways: (1) by the compiler when it sees an anonymous function that needs to be converted to an expression tree, and; (2) by a query operator method that constructs a new queryable object with an expression tree rooted in a call to the operator method (self-referential). Next we hit the foreach block. At this point, the power of LINQ queries becomes apparent. The provider is able to determine how the query expression tree is evaluated! The code that began our story was intentionally vague about the definition of the “products” collection. Maybe it is a queryable in-memory collection of products: var products = new[]     { new Product { Name = "Widget", ProductID = 1 } }.AsQueryable(); The in-memory LINQ provider works by rewriting Queryable method calls to Enumerable method calls in the query expression tree. It then compiles the expression tree and evaluates it. It should be mentioned that the provider does not blindly rewrite all Queryable calls. It only rewrites a call when its arguments have been rewritten in a way that introduces a type mismatch, e.g. the first argument to Queryable.Where<Product> being rewritten as an expression of type IEnumerable<Product> from IQueryable<Product>. The type mismatch is triggered initially by a “leaf” expression like the one associated with the AsQueryable query: when the provider recognizes one of its own leaf expressions, it replaces the expression with the original IEnumerable<> constant expression. I like to think of this rewrite process as “type irritation” because the rewritten leaf expression is like a foreign body that triggers an immune response (further rewrites) in the tree. The technique ensures that only those portions of the expression tree constructed by a particular provider are rewritten by that provider: no type irritation, no rewrite. Let’s consider the behavior of an alternative LINQ provider. If “products” is a collection created by a LINQ to SQL provider: var products = new NorthwindDataContext().Products; the provider rewrites the expression tree as a SQL query that is then evaluated by your favorite RDBMS. The predicate may ultimately be evaluated using an index! In this example, the expression associated with the Products property is the “leaf” expression. StreamInsight 2.1 For the in-memory LINQ to Objects provider, a leaf is an in-memory collection. For LINQ to SQL, a leaf is a table or view. When defining a “process” in StreamInsight 2.1, what is a leaf? To StreamInsight a leaf is logic: an adapter, a sequence, or even a query targeting an entirely different LINQ provider! How do we represent the logic? Remember that a standing query may outlive the client that provisioned it. A reference to a sequence object in the client application is therefore not terribly useful. But if we instead represent the code constructing the sequence as an expression, we can host the sequence in the server: using (var server = Server.Connect(...)) {     var app = server.Applications["my application"];     var source = app.DefineObservable(() => Observable.Range(0, 10, Scheduler.NewThread));     var query = from i in source where i % 2 == 0 select i; } Example 1: defining a source and composing a query Let’s look in more detail at what’s happening in example 1. We first connect to the remote server and retrieve an existing app. Next, we define a simple Reactive sequence using the Observable.Range method. Notice that the call to the Range method is in the body of an anonymous function. This is important because it means the source sequence definition is in the form of an expression, rather than simply an opaque reference to an IObservable<int> object. The variation in Example 2 fails. Although it looks similar, the sequence is now a reference to an in-memory observable collection: var local = Observable.Range(0, 10, Scheduler.NewThread); var source = app.DefineObservable(() => local); // can’t serialize ‘local’! Example 2: error referencing unserializable local object The Define* methods support definitions of operator tree leaves that target the StreamInsight server. These methods all have the same basic structure. The definition argument is a lambda expression taking between 0 and 16 arguments and returning a source or sink. The method returns a proxy for the source or sink that can then be used for the usual style of LINQ query composition. The “define” methods exploit the compile-time C# feature that converts anonymous functions into translatable expression trees! Query composition exploits the runtime pattern that allows expression trees to be constructed by operators taking queryable and expression (Expression<>) arguments. The practical upshot: once you’ve Defined a source, you can compose LINQ queries in the familiar way using query expressions and operator combinators. Notably, queries can be composed using pull-sequences (LINQ to Objects IQueryable<> inputs), push sequences (Reactive IQbservable<> inputs), and temporal sequences (StreamInsight IQStreamable<> inputs). You can even construct processes that span these three domains using “bridge” method overloads (ToEnumerable, ToObservable and To*Streamable). Finally, the targeted rewrite via type irritation pattern is used to ensure that StreamInsight computations can leverage other LINQ providers as well. Consider the following example (this example depends on Interactive Extensions): var source = app.DefineEnumerable((int id) =>     EnumerableEx.Using(() =>         new NorthwindDataContext(), context =>             from p in context.Products             where p.ProductID == id             select p.ProductName)); Within the definition, StreamInsight has no reason to suspect that it ‘owns’ the Queryable.Where and Queryable.Select calls, and it can therefore defer to LINQ to SQL! Let’s use this source in the context of a StreamInsight process: var sink = app.DefineObserver(() => Observer.Create<string>(Console.WriteLine)); var query = from name in source(1).ToObservable()             where name == "Widget"             select name; using (query.Bind(sink).Run("process")) {     ... } When we run the binding, the source portion which filters on product ID and projects the product name is evaluated by SQL Server. Outside of the definition, responsibility for evaluation shifts to the StreamInsight server where we create a bridge to the Reactive Framework (using ToObservable) and evaluate an additional predicate. It’s incredibly easy to define computations that span multiple domains using these new features in StreamInsight 2.1! Regards, The StreamInsight Team

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