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• Routing Apache TracEnv

  - by fampinheiro

  Hello, i have a situation with many trac instances. They all have the same structure in the filesystem. PATH/trac1 PATH/trac2 PATH/trac3 i have this configuration <Location /trac/trac1> SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv PATH/trac1 PythonOption TracUriRoot /trac/trac1 PythonOption PYTHON_EGG_CACHE PATH/eggs/ </Location> <Location /trac/trac2> SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv PATH/trac2 PythonOption TracUriRoot /trac/trac2 PythonOption PYTHON_EGG_CACHE PATH/eggs/ </Location> <Location /trac/trac3> SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv PATH/trac3 PythonOption TracUriRoot /trac/trac3 PythonOption PYTHON_EGG_CACHE PATH/eggs/ </Location> i wonder if it's possible to do something like (TracEnvParentDir is not an option) <Location /trac/{ENV}> SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv PATH/{ENV} PythonOption TracUriRoot /trac/{ENV} PythonOption PYTHON_EGG_CACHE PATH/eggs/ </Location> Thank you for your time. EDIT: TracEnvParentDir is not an option because my structure is the following +---projs +---trac1 ¦ +---public [instance] ¦ +---t1 ¦ ¦ +---common [instance] ¦ ¦ +---g1 [instance] ¦ ¦ +---g2 [instance] ¦ ¦ +---g3 [instance] ¦ ¦ +---g4 [instance] ¦ ¦ +---g5 [instance] ¦ +---t2 ¦ ¦ +---common [instance] ¦ ¦ +---g1 [instance] ¦ ¦ +---g2 [instance] ¦ ¦ +---g3 [instance] ¦ ¦ +---g4 [instance] ¦ ¦ +---g5 [instance] ¦ +---t3 ¦ +---common [instance] ¦ +---g1 [instance] ¦ +---g2 [instance] ¦ +---g3 [instance] ¦ +---g4 [instance] ¦ +---g5 [instance] ¦ +---trac2 +---public [instance] +---t1 ¦ +---common [instance] ¦ +---g1 [instance] ¦ +---g2 [instance] ¦ +---g3 [instance] ¦ +---g4 [instance] ¦ +---g5 [instance] +---t2 ¦ +---common [instance] ¦ +---g1 [instance] ¦ +---g2 [instance] ¦ +---g3 [instance] ¦ +---g4 [instance] ¦ +---g5 [instance] +---t3 +---common [instance] +---g1 [instance] +---g2 [instance] +---g3 [instance] +---g4 [instance] +---g5 [instance] I use the TracEnvParentDir on t1, t2 and t3 and TracEnv on trac1/public and trac2/public I wonder if it's possible to define a part of the url variable.

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• evaluating cost/benefits of using extension methods in C# => 3.0

  - by BillW

  Hi, In what circumstances (usage scenarios) would you choose to write an extension rather than sub-classing an object ? < full disclosure : I am not an MS employee; I do not know Mitsu Furota personally; I do know the author of the open-source Componax library mentioned here, but I have no business dealings with him whatsoever; I am not creating, or planning to create any commercial product using extensions : in sum : this post is from pure intellectal curiousity related to my trying to (continually) become aware of "best practices" I find the idea of extension methods "cool," and obviously you can do "far-out" things with them as in the many examples you can in Mitsu Furota's (MS) blog postslink text. A personal friend wrote the open-source Componax librarylink text, and there's some remarkable facilities in there; but he is in complete command of his small company with total control over code guidelines, and every line of code "passes through his hands." While this is speculation on my part : I think/guess other issues might come into play in a medium-to-large software team situation re use of Extensions. Looking at MS's guidelines at link text, you find : In general, you will probably be calling extension methods far more often than implementing your own. ... In general, we recommend that you implement extension methods sparingly and only when you have to. Whenever possible, client code that must extend an existing type should do so by creating a new type derived from the existing type. For more information, see Inheritance (C# Programming Guide). ... When the compiler encounters a method invocation, it first looks for a match in the type's instance methods. If no match is found, it will search for any extension methods that are defined for the type, and bind to the first extension method that it finds. And at Ms's link text : Extension methods present no specific security vulnerabilities. They can never be used to impersonate existing methods on a type, because all name collisions are resolved in favor of the instance or static method defined by the type itself. Extension methods cannot access any private data in the extended class. Factors that seem obvious to me would include : I assume you would not write an extension unless you expected it be used very generally and very frequently. On the other hand : couldn't you say the same thing about sub-classing ? Knowing we can compile them into a seperate dll, and add the compiled dll, and reference it, and then use the extensions : is "cool," but does that "balance out" the cost inherent in the compiler first having to check to see if instance methods are defined as described above. Or the cost, in case of a "name clash," of using the Static invocation methods to make sure your extension is invoked rather than the instance definition ? How frequent use of Extensions would affect run-time performance or memory use : I have no idea. So, I'd appreciate your thoughts, or knowing about how/when you do, or don't do, use Extensions, compared to sub-classing. thanks, Bill

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• Recreating a workflow instance with the same instance id

  - by Miron Brezuleanu

  We have some objects that have an associated workflow instance. The objects are identified with a GUID, which is also the GUID of the workflow instance associated with the object. We need to restart (see NOTE 3 for the meaning of 'restart') the workflow instance if the workflow definition changed (there is no state in the workflow itself and it is written to support restarting in this manner). The restarting is performed by calling Terminate on the WorkflowInstance, then recreating the instance with the same GUID. The weird part is that this works every other attempt (odd attempts - the workflow is stopped, but for some reason doesn't restart, even attempt - the already terminated workflow is recreated and started successfully). While I admit that using 'second hand' GUIDs is a sign of extraordinary cheapness (and something we plan to change), I'm wondering why this isn't working. Any ideas? NOTES: The terminated workflow instance is passivated (waiting for a notification) at the time of the termination. The Terminate call successfully deletes the data persisted in the database for that instance. We're using 'restarting' with a meaning that's less common in the context of WF - not restarting a passivated instance, but force the workflow to start again from the beginning of its definition. Thanks!

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• How to bundle extension methods requiring configuration in a library

  - by Greg

  Hi, I would like to develop a library that I can re-use to add various methods involved in navigating/searching through a graph (nodes/relationships, or if you like vertexs/edges). The generic requirements would be: There are existing classes in the main project that already implement the equivalent of the graph class (which contains the lists of nodes / relationships), node class and relationship class (which links nodes together) - the main project likely already has persistence mechanisms for the info (e.g. these classes might be built using Entity Framework for persistance) Methods would need to be added to each of these 3 classes: (a) graph class - methods like "search all nodes", (b) node class - methods such as "find all children to depth i", c) relationship class - methods like "return relationship type", "get parent node", "get child node". I assume there would be a need to inform the library with the extending methods the class names for the graph/node/relationships table (as different project might use different names). To some extent it would need to be like how a generics collection works (where you pass the classes to the collection so it knows what they are). Need to be a way to inform the library of which node property to use for equality checks perhaps (e.g. if it were a graph of webpages the equality field to use might be the URI path) I'm assuming that using abstract base classes wouldn't really work as this would tie usage down to have to use the same persistence approach, and same class names etc. Whereas really I want to be able to, for a project that has "graph-like" characteristics, the ability to add graph searching/walking methods to it.

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• Make methods that do not depend on instance fields, static?

  - by m3th0dman

  Recently I started programming in Groovy for a integration testing framework, for a Java project. I use Intellij IDEA with Groovy plug-in and I am surprised to see as a warning for all the methods that are non-static and do not depend on any instance fields. In Java, however, this is not an issue (at least from IDE's point of view). Should all methods that do not depend onto any instance fields be transformed into static functions? If true, is this specific to Groovy or it is available for OOP in general? And why?

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• Creating Haskell instance declarations

  - by btl

  Hello, complete noob to Haskell here with probably an even noobier question. I'm trying to get ghci output working and am stuck on instance declarations. How could I declare an instance for "(Show (Stack - Stack))" given: data Cmd = LD Int | ADD | MULT | DUP deriving Show type Prog = [Cmd] type Stack = [Int] type D = Stack -> Stack I've been trying to create a declaration like: instance Show D where show = Stack but all my attempts have resulted in illegal instance declarations. Any help and/or references much appreciated!

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• In Ruby are there any related applications of the syntax: class << self ... end

  - by pez_dispenser

  class << self attr_accessor :n, :totalX, :totalY end The syntax above is used for defining class instance variables. But when I think about what syntax implies, it doesn't make any sense to me, so I'm wondering if this type of syntax is used for any other types of definitions. My point of confusion here is this: class << self The append operator normally means "add what's on the right to the object on the left". But in the context of this block, how does that add up to "put the contents of this block into the definition of the class instance rather than the instance"? For the same reason I'm confused as to why in one context class << self can define class instance variables while in another it seems to create class variables such as here: class Point # Instance methods go here class << self # Class methods go here end end

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• "Cannot open user default database" error with "User Instance=True"

  - by Keith

  I have a desktop application that uses Sql user instancing. This is my connection string: "Data Source=.\SqlExpress; AttachDbFilename=C:\path\file.mdf; Integrated Security=True; User Instance=True; Connect Timeout=100;" My application creates this DB, downloads a load of data into it from a web service and then does a lot of actions with it. The problem comes when I attempt to re-open the connection. I get a SqlException: "Cannot open user default database. Login failed. Login failed for user 'myDomain\myusername'." This error makes no sense in this context - I have no default database. I'm logging in to an instance created just for the current application, running separately from SqlExpress. There's no other way to connect to this DB. If I start the SqlExpress service and connect to the default instance it won't be visible. It only exists for this application. The file on disk is locked by the SqlExpress instance service running under the application. if I stop the app and restart it the connection works first time, but fails on re-opening. If I just stop the app I can delete the .mdf files and begin again, but it still crashes when I re-open the connection. As my app started the instance running as me my current user should have access to every DB in the instance. This doesn't happen for other users of the same code, which suggests that it's a SQL config issue. Does anyone have any idea what causes this and how to work around it?

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• Stepping into Ruby Meta-Programming: Generating proxy methods for multiple internal methods

  - by mstksg

  Hi all; I've multiply heard Ruby touted for its super spectacular meta-programming capabilities, and I was wondering if anyone could help me get started with this problem. I have a class that works as an "archive" of sorts, with internal methods that process and output data based on an input. However, the items in the archive in the class itself are represented and processed with integers, for performance purposes. The actual items outside of the archive are known by their string representation, which is simply number_representation.to_s(36). Because of this, I have hooked up each internal method with a "proxy method" that converts the input into the integer form that the archive recognizes, runs the internal method, and converts the output (either a single other item, or a collection of them) back into strings. The naming convention is this: internal methods are represented by _method_name; their corresponding proxy method is represented by method_name, with no leading underscore. For example: class Archive ## PROXY METHODS ## ## input: string representation of id's ## output: string representation of id's def do_something_with id result = _do_something_with id.to_i(36) return nil if result == nil return result.to_s(36) end def do_something_with_pair id_1,id_2 result = _do_something_with_pair id_1.to_i(36), id_2.to_i(36) return nil if result == nil return result.to_s(36) end def do_something_with_these ids result = _do_something_with_these ids.map { |n| n.to_i(36) } return nil if result == nil return result.to_s(36) end def get_many_from id result = _get_many_from id return nil if result == nil # no sparse arrays returned return result.map { |n| n.to_s(36) } end ## INTERNAL METHODS ## ## input: integer representation of id's ## output: integer representation of id's def _do_something_with id # does something with one integer-represented id, # returning an id represented as an integer end def do_something_with_pair id_1,id_2 # does something with two integer-represented id's, # returning an id represented as an integer end def _do_something_with_these ids # does something with multiple integer ids, # returning an id represented as an integer end def _get_many_from id # does something with one integer-represented id, # returns a collection of id's represented as integers end end There are a couple of reasons why I can't just convert them if id.class == String at the beginning of the internal methods: These internal methods are somewhat computationally-intensive recursive functions, and I don't want the overhead of checking multiple times at every step There is no way, without adding an extra parameter, to tell whether or not to re-convert at the end I want to think of this as an exercise in understanding ruby meta-programming Does anyone have any ideas? edit The solution I'd like would preferably be able to take an array of method names @@PROXY_METHODS = [:do_something_with, :do_something_with_pair, :do_something_with_these, :get_many_from] iterate through them, and in each iteration, put out the proxy method. I'm not sure what would be done with the arguments, but is there a way to test for arguments of a method? If not, then simple duck typing/analogous concept would do as well.

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• Get and Set property accessors are ‘actually’ methods

  - by nmarun

  Well, they are ‘special’ methods, but they indeed are methods. See the class below: 1: public class Person 2: { 3: private string _name; 4:  5: public string Name 6: { 7: get 8: { 9: return _name; 10: } 11: set 12: { 13: if (value == "aaa") 14: { 15: throw new ArgumentException("Invalid Name"); 16: } 17: _name = value; 18: } 19: } 20:  21: public void Save() 22: { 23: Console.WriteLine("Saving..."); 24: } 25: } Ok, so a class with a field, a property with the get and set accessors and a method. Now my calling code says: 1: static void Main() 2: { 3: try 4: { 5: Person person1 = new Person 6: { 7: Name = "aaa", 8: }; 9:  10: } 11: catch (Exception ex) 12: { 13: Console.WriteLine(ex.Message); 14: Console.WriteLine(ex.StackTrace); 15: Console.WriteLine("--------------------"); 16: } 17: } When the code is run, you’ll get the following exception message displayed: Now, you see the first line of the stack trace where it says that the exception was thrown in the method set_Name(String value). Wait a minute, we have not declared any method with that name in our Person class. Oh no, we actually have. When you create a property, this is what happens behind the screen. The CLR creates two methods for each get and set property accessor. Let’s look at the signature once again: set_Name(String value) This also tells you where the ‘value’ keyword comes from in our set property accessor. You’re actually wiring up a method parameter to a field. 1: set 2: { 3: if (value == "aaa") 4: { 5: throw new ArgumentException("Invalid Name"); 6: } 7: _name = value; 8: } Digging deeper on this, I ran the ILDasm tool and this is what I see: We see the ‘free’ constructor (named .ctor) that the compiler gives us, the _name field, the Name property and the Save method. We also see the get_Name and set_Name methods. In order to compare the Save and the set_Name methods, I double-clicked on the two methods and this is what I see: The ‘.method’ keyword tells that both Save and set_Name are both methods (no guessing there!). Seeing the set_Name method as a public method did kinda surprise me. So I said, why can’t I do a person1.set_Name(“abc”) since it is declared as public. This cannot be done because the get_Name and set_Name methods have an extra attribute called ‘specialname’. This attribute is used to identify an IL (Intermediate Language) token that can be treated with special care by the .net language. So the thumb-rule is that any method with the ‘specialname’ attribute cannot be generally called / invoked by the user (a simple test using intellisense proves this). Their functionality is exposed through other ways. In our case, this is done through the property itself. The same concept gets extended to constructors as well making them special methods too. These so-called ‘special’ methods can be identified through reflection. 1: static void ReflectOnPerson() 2: { 3: Type personType = typeof(Person); 4:  5: MethodInfo[] methods = personType.GetMethods(); 6:  7: for (int i = 0; i < methods.Length; i++) 8: { 9: Console.Write("Method: {0}", methods[i].Name); 10: // Determine whether or not each method is a special name. 11: if (methods[i].IsSpecialName) 12: { 13: Console.Write(" has 'SpecialName' attribute"); 14: } 15: Console.WriteLine(); 16: } 17: } Line 11 shows the ‘IsSpecialName’ boolean property. So a method with a ‘specialname’ attribute gets mapped to the IsSpecialName property. The output is displayed as: Wuhuuu! There they are.. our special guests / methods. Verdict: Getting to know the internals… helps!

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• EC2 instance suddenly refusing SSH connections and won't respond to ping

  - by Chris

  My instance was running fine and this morning I was able to access a Ruby on Rails app hosted on it. An hour later I suddenly wasn't able to access my site, my SSH connection attempts were refused and the server wasn't even responding to ping. I didn't change anything on my system during that hour and reboots aren't fixing it. I've never had any problems connecting or pinging the system before. Can someone please help? This is on my production system! OS: CentOS 5 AMI ID: ami-10b55379 Type: m1.small [] ~% ssh -v *****@meeteor.com OpenSSH_5.2p1, OpenSSL 0.9.8l 5 Nov 2009 debug1: Reading configuration data /etc/ssh_config debug1: Connecting to meeteor.com [184.73.235.191] port 22. debug1: connect to address 184.73.235.191 port 22: Connection refused ssh: connect to host meeteor.com port 22: Connection refused [] ~% ping meeteor.com PING meeteor.com (184.73.235.191): 56 data bytes Request timeout for icmp_seq 0 Request timeout for icmp_seq 1 Request timeout for icmp_seq 2 ^C --- meeteor.com ping statistics --- 4 packets transmitted, 0 packets received, 100.0% packet loss [] ~% ========= System Log ========= Restarting system. Linux version 2.6.16-xenU ([email protected]) (gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)) #1 SMP Mon May 28 03:41:49 SAST 2007 BIOS-provided physical RAM map: Xen: 0000000000000000 - 000000006a400000 (usable) 980MB HIGHMEM available. 727MB LOWMEM available. NX (Execute Disable) protection: active IRQ lockup detection disabled Built 1 zonelists Kernel command line: root=/dev/sda1 ro 4 Enabling fast FPU save and restore... done. Enabling unmasked SIMD FPU exception support... done. Initializing CPU#0 PID hash table entries: 4096 (order: 12, 65536 bytes) Xen reported: 2599.998 MHz processor. Dentry cache hash table entries: 131072 (order: 7, 524288 bytes) Inode-cache hash table entries: 65536 (order: 6, 262144 bytes) Software IO TLB disabled vmalloc area: ee000000-f53fe000, maxmem 2d7fe000 Memory: 1718700k/1748992k available (1958k kernel code, 20948k reserved, 620k data, 144k init, 1003528k highmem) Checking if this processor honours the WP bit even in supervisor mode... Ok. Calibrating delay using timer specific routine.. 5202.30 BogoMIPS (lpj=26011526) Mount-cache hash table entries: 512 CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line) CPU: L2 Cache: 1024K (64 bytes/line) Checking 'hlt' instruction... OK. Brought up 1 CPUs migration_cost=0 Grant table initialized NET: Registered protocol family 16 Brought up 1 CPUs xen_mem: Initialising balloon driver. highmem bounce pool size: 64 pages VFS: Disk quotas dquot_6.5.1 Dquot-cache hash table entries: 1024 (order 0, 4096 bytes) Initializing Cryptographic API io scheduler noop registered io scheduler anticipatory registered (default) io scheduler deadline registered io scheduler cfq registered i8042.c: No controller found. RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize Xen virtual console successfully installed as tty1 Event-channel device installed. netfront: Initialising virtual ethernet driver. mice: PS/2 mouse device common for all mice md: md driver 0.90.3 MAX_MD_DEVS=256, MD_SB_DISKS=27 md: bitmap version 4.39 NET: Registered protocol family 2 Registering block device major 8 IP route cache hash table entries: 65536 (order: 6, 262144 bytes) TCP established hash table entries: 262144 (order: 9, 2097152 bytes) TCP bind hash table entries: 65536 (order: 7, 524288 bytes) TCP: Hash tables configured (established 262144 bind 65536) TCP reno registered TCP bic registered NET: Registered protocol family 1 NET: Registered protocol family 17 NET: Registered protocol family 15 Using IPI No-Shortcut mode md: Autodetecting RAID arrays. md: autorun ... md: ... autorun DONE. kjournald starting. Commit interval 5 seconds EXT3-fs: mounted filesystem with ordered data mode. VFS: Mounted root (ext3 filesystem) readonly. Freeing unused kernel memory: 144k freed *************************************************************** *************************************************************** ** WARNING: Currently emulating unsupported memory accesses ** ** in /lib/tls glibc libraries. The emulation is ** ** slow. To ensure full performance you should ** ** install a 'xen-friendly' (nosegneg) version of ** ** the library, or disable tls support by executing ** ** the following as root: ** ** mv /lib/tls /lib/tls.disabled ** ** Offending process: init (pid=1) ** *************************************************************** *************************************************************** Pausing... 5Pausing... 4Pausing... 3Pausing... 2Pausing... 1Continuing... INIT: version 2.86 booting Welcome to CentOS release 5.4 (Final) Press 'I' to enter interactive startup. Setting clock : Fri Oct 1 14:35:26 EDT 2010 [ OK ] Starting udev: [ OK ] Setting hostname localhost.localdomain: [ OK ] No devices found Setting up Logical Volume Management: [ OK ] Checking filesystems Checking all file systems. [/sbin/fsck.ext3 (1) -- /] fsck.ext3 -a /dev/sda1 /dev/sda1: clean, 275424/1310720 files, 1161123/2621440 blocks [ OK ] Remounting root filesystem in read-write mode: [ OK ] Mounting local filesystems: [ OK ] Enabling local filesystem quotas: [ OK ] Enabling /etc/fstab swaps: [ OK ] INIT: Entering runlevel: 4 Entering non-interactive startup Starting background readahead: [ OK ] Applying ip6tables firewall rules: modprobe: FATAL: Module ip6_tables not found. ip6tables-restore v1.3.5: ip6tables-restore: unable to initializetable 'filter' Error occurred at line: 3 Try `ip6tables-restore -h' or 'ip6tables-restore --help' for more information. [FAILED] Applying iptables firewall rules: [ OK ] Loading additional iptables modules: ip_conntrack_netbios_ns [ OK ] Bringing up loopback interface: [ OK ] Bringing up interface eth0: Determining IP information for eth0... done. [ OK ] Starting auditd: [FAILED] Starting irqbalance: [ OK ] Starting portmap: [ OK ] FATAL: Module lockd not found. Starting NFS statd: [ OK ] Starting RPC idmapd: FATAL: Module sunrpc not found. FATAL: Error running install command for sunrpc Error: RPC MTAB does not exist. Starting system message bus: [ OK ] Starting Bluetooth services:[ OK ] [ OK ] Can't open RFCOMM control socket: Address family not supported by protocol Mounting other filesystems: [ OK ] Starting PC/SC smart card daemon (pcscd): [ OK ] Starting hidd: Can't open HIDP control socket: Address family not supported by protocol [FAILED] Starting autofs: Starting automount: automount: test mount forbidden or incorrect kernel protocol version, kernel protocol version 5.00 or above required. [FAILED] [FAILED] Starting sshd: [ OK ] Starting cups: [ OK ] Starting sendmail: [ OK ] Starting sm-client: [ OK ] Starting console mouse services: no console device found[FAILED] Starting crond: [ OK ] Starting xfs: [ OK ] Starting anacron: [ OK ] Starting atd: [ OK ] % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 390 100 390 0 0 58130 0 --:--:-- --:--:-- --:--:-- 58130 100 390 100 390 0 0 56984 0 --:--:-- --:--:-- --:--:-- 0 Starting yum-updatesd: [ OK ] Starting Avahi daemon... [ OK ] Starting HAL daemon: [ OK ] Starting OSSEC: [ OK ] Starting smartd: [ OK ] c CentOS release 5.4 (Final) Kernel 2.6.16-xenU on an i686 domU-12-31-39-00-C4-97 login: INIT: Id "2" respawning too fast: disabled for 5 minutes INIT: Id "3" respawning too fast: disabled for 5 minutes INIT: Id "4" respawning too fast: disabled for 5 minutes INIT: Id "5" respawning too fast: disabled for 5 minutes INIT: Id "6" respawning too fast: disabled for 5 minutes

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• Extension Methods and Application Code

  - by Mystagogue

  I have seen plenty of online guidelines for authoring extension methods, usually along these lines: 1) Avoid authoring extension methods when practical - prefer other approaches first (e.g. regular static methods). 2) Don't author extension methods to extend code you own or currently develop. Instead, author them to extend 3rd party or BCL code. But I have the impression that a couple more guidelines are either implied or advisable. What does the community think of these two additional guidelines: A) Prefer to author extension methods to contain generic functionality rather than application-specific logic. (This seems to follow from guideline #2 above) B) An extension method should be sizeable enough to justify itself (preferably at least 5 lines of code in length). Item (B) is intended to discourage a develoer from writing dozens of extension methods (totalling X lines of code) to refactor or replace what originally was already about X lines of inline code. Perhaps item (B) is badly qualified, or even misinformed about how a one line extension method is actually powerful and justified. I'm curious to know. But if item (B) is somehow dismissed by the community, I must admist I'm still particularly interested in feedback on guideline (A).

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• Extension methods for encapsulation and reusability

  - by tzaman

  In C++ programming, it's generally considered good practice to "prefer non-member non-friend functions" instead of instance methods. This has been recommended by Scott Meyers in this classic Dr. Dobbs article, and repeated by Herb Sutter and Andrei Alexandrescu in C++ Coding Standards (item 44); the general argument being that if a function can do its job solely by relying on the public interface exposed by the class, it actually increases encapsulation to have it be external. While this confuses the "packaging" of the class to some extent, the benefits are generally considered worth it. Now, ever since I've started programming in C#, I've had a feeling that here is the ultimate expression of the concept that they're trying to achieve with "non-member, non-friend functions that are part of a class interface". C# adds two crucial components to the mix - the first being interfaces, and the second extension methods: Interfaces allow a class to formally specify their public contract, the methods and properties that they're exposing to the world. Any other class can choose to implement the same interface and fulfill that same contract. Extension methods can be defined on an interface, providing any functionality that can be implemented via the interface to all implementers automatically. And best of all, because of the "instance syntax" sugar and IDE support, they can be called the same way as any other instance method, eliminating the cognitive overhead! So you get the encapsulation benefits of "non-member, non-friend" functions with the convenience of members. Seems like the best of both worlds to me; the .NET library itself providing a shining example in LINQ. However, everywhere I look I see people warning against extension method overuse; even the MSDN page itself states: In general, we recommend that you implement extension methods sparingly and only when you have to. So what's the verdict? Are extension methods the acme of encapsulation and code reuse, or am I just deluding myself?

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• How to prevent duplicate data access methods that retrieve similar data?

  - by Ronald Wildenberg

  In almost every project I work on with a team, the same problem seems to creep in. Someone writes UI code that needs data and writes a data access method: AssetDto GetAssetById(int assetId) A week later someone else is working on another part of the application and also needs an AssetDto but now including 'approvers' and writes the following: AssetDto GetAssetWithApproversById(int assetId) A month later someone needs an asset but now including the 'questions' (or the 'owners' or the 'running requests', etc): AssetDto GetAssetWithQuestionsById(int assetId) AssetDto GetAssetWithOwnersById(int assetId) AssetDto GetAssetWithRunningRequestsById(int assetId) And it gets even worse when methods like GetAssetWithOwnerAndQuestionsById start to appear. You see the pattern that emerges: an object is attached to a large object graph and you need different parts of this graph in different locations. Of course, I'd like to prevent having a large number of methods that do almost the same. Is it simply a matter of team discipline or is there some pattern I can use to prevent this? In some cases it might make sense to have separate methods, i.e. getting an asset with running requests may be expensive so I do not want to include these all the time. How to handle such cases?

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• setting value to the instance of primitive types

  - by Samreen

  I have a function which performs some operation i.e. fetches some data from database. The generic it takes is primitive type always i.e. int, char, bool, string etc. I can easily create its instance. But I can't set the value that I have fetched from database to this instance. public T PerformOperation<T>() { object instance = (T)Activator.CreateInstance(typeof(T)); object result=FetchData(); instance = (T)result; //It gives error on this statement } The function is called as: int result = PerformOperation<int>(); Is there some way of casting the object Type to any generic type which is always primitive?

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• Return the name of the class instance with the highest 'someValue' instance variable

  - by Timbo

  I have a brand new Objective-C class called test. The test class has an instance variable called someValue, which contains an integer. I create 5 instances of the test class called aTest, bTest, cTest, dTest and eTest. The appropriate synthesize and property declarations for someValue are in place. Is there a clean way of returning the name of the class instance with the highest someValue value out of all the existing test class instances? The number of class instances may vary from the 5 in my example. Note I don't care what the value is, I just want to return the name of the class instance with the highest 'someValue' instance variable. I've tried a few NSMutable arrays however can only get the value not the name of the variable that contains it. Thanks in advance

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• Obtaining reference to Class instance by string name - VB.NET

  - by Jeff Williams

  Is it possible using Reflection or some other method to obtain a reference to a specific class instance from the name of that class instance? For example the framework for the applications i develop heavily uses public class instances such as: Public bMyreference as MyReference = new MyReference Then throughout the application bMyReference is used by custom controls and code. One of the properties of the custom controls is the "FieldName" which references a Property in these class instances (bMyReference.MyField) as a string. What i would like to be able to do is analyze this string "bMyReference.MyField" and then refer back to the actual Instance/Property. In VB6 I would use an EVAL or something simular to convert the string to an actual object but this obviously doesn't work in VB.net What I'm picturing is something like this Dim FieldName as String = MyControl.FieldName ' sets FielName to bMyReference.MyField Dim FieldObject() as String = FieldName.Split(".") ' Split into the Object / Property Dim myInstance as Object = ......... ' Obtain a reference to the Instance and set as myInstance Dim myProperty = myInstance.GetType().GetProperty(FieldObject(1))

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• How to get an instance of instance System.Diagnostics.Process by processID on a remote machine

  - by Tomas1

  Hi all, I want to run & control a process remotely, I found the best way is the WMI APIs, The WMI gives me information about the remote process but I need more control like waiting it and getting the standard output and errors, how can I do that, and can I get an instance of System.Diagnostics.Process class by instance ID remotely? note: I tried to get an instance of the Process by Process.GetProcessByPID and passign machineName parameter, but and Exception has thrown. Thanks in advance.

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• Use python decorators on class methods and subclass methods

  - by AlexH

  Goal: Make it possible to decorate class methods. When a class method gets decorated, it gets stored in a dictionary so that other class methods can reference it by a string name. Motivation: I want to implement the equivalent of ASP.Net's WebMethods. I am building this on top of google app engine, but that does not affect the point of difficulty that I am having. How it Would look if it worked: class UsefulClass(WebmethodBaseClass): def someMethod(self, blah): print(blah) @webmethod def webby(self, blah): print(blah) # the implementation of this class could be completely different, it does not matter # the only important thing is having access to the web methods defined in sub classes class WebmethodBaseClass(): def post(self, methodName): webmethods[methodName]("kapow") ... a = UsefulClass() a.post("someMethod") # should error a.post("webby") # prints "kapow" There could be other ways to go about this. I am very open to suggestions

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• Are Magic Methods Best practice in PHP?

  - by Parth

  Are Magic Methods Best practice in PHP?

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• To static or not to static

  - by Idsa

  I really like to use static methods (especially for helpers classes). But as static methods are not stubbable, eventually they are a bad practice, aren't they? So I have to choose between static methods usage convenience and testability. Is there any compromise?

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• Information on Rojiani's Numerical methods C textbook

  - by yCalleecharan

  Hi, having taken a look at a few textbooks that discuss numerical methods and C programming, I was gladly surprised when browsing through "programming in C with numerical methods for engineers" by Rojiani. I understand of course it's important that one need to have a solid background in numerical methods prior to try implementing them on a computer. I would like to know if someone here has been using this book and if possible point out strengths and weaknesses of this textbook. Thanks a lot...

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• Refering to javascript instance methods with a pound/hash sign

  - by Josh

  This question is similar to http://stackoverflow.com/questions/736120/why-are-methods-in-ruby-documentation-preceded-by-a-pound-sign I understand why in Ruby instance methods are proceeded with a pound sign, helping to differentiate talking about SomeClass#someMethod from SomeObject.someMethod and allowing rdoc to work. And I understand that the authors of PrototypeJS admire Ruby (with good reason) and so they use the hash mark convention in their documentation. My question is: is this a standard practice amongst JavaScript developers or is it just Prototype developers who do this? Asked another way, is it proepr for me to refer to instance methods in comments/documentation as SomeClass#someMethod? Or should my documentation refer to `SomeClass.someMethod?

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• What are your most useful C# extension methods?

  - by Edward Tanguay

  Extension methods continually make the C# I work with more readable and intuitive to program. I want to collect useful extension methods into a library so I always have them, such FormatWith by James Newton-King. What are the most useful extension methods that you use?

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• object / class methods serialized as well?

  - by Mat90

  I know that data members are saved to disk but I was wondering whether object's/class' methods are saved in binary format as well? Because I found some contradictionary info, for example: Ivor Horton: "Class objects contain function members as well as data members, and all the members, both data and functions, have access specifiers; therefore, to record objects in an external file, the information written to the file must contain complete specifications of all the class structures involved." and: Are methods also serialized along with the data members in .NET? Thus: are method's assembly instructions (opcodes and operands) stored to disk as well? Just like a precompiled LIB or DLL? During the DOS ages I used assembly so now and then. As far as I remember from Delphi and the following site (answer by dan04): Are methods also serialized along with the data members in .NET? sizeof(<OBJECT or CLASS>) will give the size of all data members together (no methods/procedures). Also a nice C example is given there with data and members declared in one class/struct but at runtime these methods are separate procedures acting on a struct of data. However, I think that later class/object implementations like Pascal's VMT may be different in memory.

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