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• Properly design a code editor application

  - by Hemaulo

  I'm working on personal project which is basically a code editor. Imagine standard File menu with menu items New, Open, Save, Save As, Save All, Close, Close All. I'm stuck with proper design. Currently I have: A Document class which represents a document - code editing control, respective tab in tab bar and various properties such as Caption, Filename, IsModified etc. A Documents class which represents all open documents. Contains methods like New, Open(FileName), ... The problem is that I can't figure out which class / menu command is responsible for which tasks. For example, with File-New menu command is simple - call Documents.New and that's it. But what for File-Open? The Documents.Open method expects filename as a parameter. So before calling this method I need to open an file selection dialog, let user select files and for each file call Documents.Open(FileName). Where is best place for this supporting code, in menu command, rewrite Documents.Open and put it there? The same with Save actions. Which is responsible for saving? Is it Documents class which uses Document.Editor.SaveToFile(FileName) or better create Save method in Document class? Somewhere in the middle also need to ask user if he wants to save current document... I'm stuck. Any ideas? Edited: The programming language is Delphi.

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• Execute Stored Procedure from Classic ASP

  - by Jaco Pretorius

  For some fantastic reason I find myself debugging a problem in a Classic ASP page (at least 10 years of my life lost in the last 2 days). I'm trying to execute a stored procedure which contains some OUT parameters. The problem is that one of the OUT parameters is not being populated when the stored procedure returns. I can execute the stored proc from SQL management studio (this is 2008) and all the values are being set and returned exactly as expected. declare @inVar1 varchar(255) declare @inVar2 varchar(255) declare @outVar1 varchar(255) declare @outVar2 varchar(255) SET @inVar2 = 'someValue' exec theStoredProc @inVar1 , @inVar2 , @outVar1 OUT, @outVar2 OUT print '@outVar1=' + @outVar1 print '@outVar2=' + @outVar2 Works great. Fantastic. Perfect. The exact values that I'm expecting are being returned and printed out. Right, since I'm trying to debug a Classic ASP page I copied the code into a VBScript file to try and narrow down the problem. Here is what I came up with: Set Conn = CreateObject("ADODB.Connection") Conn.Open "xxx" Set objCommandSec = CreateObject("ADODB.Command") objCommandSec.ActiveConnection = Conn objCommandSec.CommandType = 4 objCommandSec.CommandText = "theStoredProc " objCommandSec.Parameters.Refresh objCommandSec.Parameters(2) = "someValue" objCommandSec.Execute MsgBox(objCommandSec.Parameters(3)) Doesn't work. Not even a little bit. (Another ten years of my life down the drain) The third parameter is simply NULL - which is what I'm experiencing in the Classic ASP page as well. Could someone shed some light on this? Am I completely daft for thinking that the classic ASP code would be the same as the VBScript code? I think it's using the same scripting engine and syntax so I should be ok, but I'm not 100% sure. The result I'm seeing from my VBScript is the same as I'm seeing in ASP.

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• MediaFileUpload of HTML in UTF-8 encoding using Python and Google-Drive-SDK

  - by Victoria

  Looking for example using MediaFileUpload has a reference to the basic documentation for creating/uploading a file to Google Drive. However, while I have code that creates files, converting from HTML to Google Doc format. It works perfectly when they contain only ASCII characters, but when I add a non-ASCII character, it fails, with the following traceback: Traceback (most recent call last): File "d:\my\py\ckwort.py", line 949, in <module> rids, worker_documents = analyze( meta, gd ) File "d:\my\py\ckwort.py", line 812, in analyze gd.mkdir( **iy ) File "d:\my\py\ckwort.py", line 205, in mkdir self.create( **( kw['subop'])) File "d:\my\py\ckwort.py", line 282, in create media_body=kw['media_body'], File "D:\my\py\gdrive2\oauth2client\util.py", line 120, in positional_wrapper return wrapped(*args, **kwargs) File "D:\my\py\gdrive2\apiclient\http.py", line 676, in execute headers=self.headers) File "D:\my\py\gdrive2\oauth2client\util.py", line 120, in positional_wrapper return wrapped(*args, **kwargs) File "D:\my\py\gdrive2\oauth2client\client.py", line 420, in new_request redirections, connection_type) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1597, in request (response, content) = self._request(conn, authority, uri, request_uri, method, body, headers, redirections, cachekey) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1345, in _request (response, content) = self._conn_request(conn, request_uri, method, body, headers) File "D:\my\py\gdrive2\httplib2\__init__.py", line 1282, in _conn_request conn.request(method, request_uri, body, headers) File "C:\Python27\lib\httplib.py", line 958, in request self._send_request(method, url, body, headers) File "C:\Python27\lib\httplib.py", line 992, in _send_request self.endheaders(body) File "C:\Python27\lib\httplib.py", line 954, in endheaders self._send_output(message_body) File "C:\Python27\lib\httplib.py", line 812, in _send_output msg += message_body UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 370: ordinal not in range(128) I don't find any parameter to use to specify what file encoding should be used by MediaFileUpload (My files are using UTF-8). Am I missing something?

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• KeyStore, HttpClient, and HTTPS: Can someone explain this code to me?

  - by stormin986

  I'm trying to understand what's going on in this code. KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType()); FileInputStream instream = new FileInputStream(new File("my.keystore")); try { trustStore.load(instream, "nopassword".toCharArray()); } finally { instream.close(); } SSLSocketFactory socketFactory = new SSLSocketFactory(trustStore); Scheme sch = new Scheme("https", socketFactory, 443); httpclient.getConnectionManager().getSchemeRegistry().register(sch); My Questions: trustStore.load(instream, "nopassword".toCharArray()); is doing what exactly? From reading the documentation load() will load KeyStore data from an input stream (which is just an empty file we just created), using some arbitrary "nopassword". Why not just load it with null as the InputStream parameter and an empty string as the password field? And then what is happening when this empty KeyStore is being passed to the SSLSocketFactory constructor? What's the result of such an operation? Or -- is this simply an example where in a real application you would have to actually put a reference to an existing keystore file / password?

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• Choosing between instance methods and separate functions?

  - by StackedCrooked

  Adding functionality to a class can be done by adding a method or by defining a function that takes an object as its first parameter. Most programmers that I know would choose for the solution of adding a instance method. However, I sometimes prefer to create a separate function. For example, in the example code below Area and Diagonal are defined as separate functions instead of methods. I find it better this way because I think these functions provide enhancements rather than core functionality. Is this considered a good/bad practice? If the answer is "it depends", then what are the rules for deciding between adding method or defining a separate function? class Rect { public: Rect(int x, int y, int w, int h) : mX(x), mY(y), mWidth(w), mHeight(h) { } int x() const { return mX; } int y() const { return mY; } int width() const { return mWidth; } int height() const { return mHeight; } private: int mX, mY, mWidth, mHeight; }; int Area(const Rect & inRect) { return inRect.width() * inRect.height(); } float Diagonal(const Rect & inRect) { return std::sqrt(std::pow(static_cast<float>(inRect.width()), 2) + std::pow(static_cast<float>(inRect.height()), 2)); }

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• Botan linking error on Windows MSVC

  - by Jake Petroules

  I am trying to compile a library linking to the version of Botan from the Qt Creator sources with MSVC 2008 but am receiving the following error. MinGW compiles and links it fine. What is the issue? databasecrypto.obj:-1: error: LNK2019: unresolved external symbol "public: static unsigned int const Botan::Pipe::DEFAULT_MESSAGE" (?DEFAULT_MESSAGE@Pipe@Botan@@2IB) referenced in function "private: static class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl DatabaseCrypto::b64_encode(class Botan::SecureVector<unsigned char> const &)" (?b64_encode@DatabaseCrypto@@CA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@ABV?$SecureVector@E@Botan@@@Z) /*! Encodes the Botan byte array \a in as a base 64 string. \param in The Botan byte array to encode. */ std::string DatabaseCrypto::b64_encode(const SecureVector<Botan::byte> &in) { Pipe pipe(new Base64_Encoder); pipe.process_msg(in); return pipe.read_all_as_string(); // <-- default parameter here is Botan::Pipe::DEFAULT_MESSAGE }

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• Why is partial specialziation of a nested class template allowed, while complete isn't?

  - by drhirsch

  template<int x> struct A { template<int y> struct B {};. template<int y, int unused> struct C {}; }; template<int x> template<> struct A<x>::B<x> {}; // error: enclosing class templates are not explicitly specialized template<int x> template<int unused> struct A<x>::C<x, unused> {}; // ok So why is the explicit specialization of a inner, nested class (or function) not allowed, if the outer class isn't specialiced too? Strange enough, I can work around this behaviour if I only partially specialize the inner class with simply adding a dummy template parameter. Makes things uglier and more complex, but it works. Note: I need this feature for recursive templates of the inner class for a set of the outer class. To make things even more complicate, in reality I only need a template function instead of the inner class. But partial specialization of functions is generally disallowed somewhere else in the standard ^^

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• How to access global variable in a view in Ruby on Rails?

  - by ben

  I have a User model. I have a Session controller, in which I have a global user variable that is assigned as follows: $user = User.authenticate(params[:session][:email], params[:session][:password]) (I've made user global just to try to solve this problem, so if there's a better way please let me know!) I need to use the email of the logged in user as a parameter to send to Flex part of my website. At the moment I'm creating the link as follows: <%= link_to "secondpage", secondpage_path(:email => @session.$user.email) But I'm getting the following error: compile error /Users/benhartney/rails_projects/talk/app/views/layouts/_header.html.erb:12: syntax error, unexpected tGVAR ..._path(:email = @session.$user.email) ).to_s); @output_buffe... There's also a little arrow pointing at $user If I remove the $ from $user, I get this error: undefined method `user' for nil:NilClass If I remove the (:email => @session.user.email) part, everything works fine, so I think all of the code except for this is ok. Can anyone tell me what I'm doing wrong? Thanks for reading!

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• In Python, how can I find the index of the first item in a list that is NOT some value?

  - by Ryan B. Lynch

  Python's list type has an index(x) method. It takes a single parameter x, and returns the (integer) index of the first item in the list that has the value x. Basically, I need to invert the index(x) method. I need to get the index of the first value in a list that does NOT have the value x. I would probably be able to even just use a function that returns the index of the first item with a value != None. I can think of a 'for' loop implementation with an incrementing counter variable, but I feel like I'm missing something. Is there an existing method, or a one-line Python construction that can handle this? In my program, the situation comes up when I'm handling lists returned from complex regex matches. All but one item in each list have a value of None. If I just needed the matched string, I could use a list comprehension like '[x for x in [my_list] if x is not None]', but I need the index in order to figure out which capture group in my regex actually caused the match.

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• Boost binding a function taking a reference

  - by Jamie Cook

  Hi all, I am having problems compiling the following snippet int temp; vector<int> origins; vector<string> originTokens = OTUtils::tokenize(buffer, ","); // buffer is a char[] array // original loop BOOST_FOREACH(string s, originTokens) { from_string(temp, s); origins.push_back(temp); } // I'd like to use this to replace the above loop std::transform(originTokens.begin(), originTokens.end(), origins.begin(), boost::bind<int>(&FromString<int>, boost::ref(temp), _1)); where the function in question is // the third parameter should be one of std::hex, std::dec or std::oct template <class T> bool FromString(T& t, const std::string& s, std::ios_base& (*f)(std::ios_base&) = std::dec) { std::istringstream iss(s); return !(iss >> f >> t).fail(); } the error I get is 1>Compiling with Intel(R) C++ 11.0.074 [IA-32]... (Intel C++ Environment) 1>C:\projects\svn\bdk\Source\deps\boost_1_42_0\boost/bind/bind.hpp(303): internal error: assertion failed: copy_default_arg_expr: rout NULL, no error (shared/edgcpfe/il.c, line 13919) 1> 1> return unwrapper<F>::unwrap(f, 0)(a[base_type::a1_], a[base_type::a2_]); 1> ^ 1> 1>icl: error #10298: problem during post processing of parallel object compilation Google is being unusually unhelpful so I hope that some one here can provide some insights.

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• Is there really such a thing as a char or short in modern programming?

  - by Dean P

  Howdy all, I've been learning to program for a Mac over the past few months (I have experience in other languages). Obviously that has meant learning the Objective C language and thus the plainer C it is predicated on. So I have stumbles on this quote, which refers to the C/C++ language in general, not just the Mac platform. With C and C++ prefer use of int over char and short. The main reason behind this is that C and C++ perform arithmetic operations and parameter passing at integer level, If you have an integer value that can fit in a byte, you should still consider using an int to hold the number. If you use a char, the compiler will first convert the values into integer, perform the operations and then convert back the result to char. So my question, is this the case in the Mac Desktop and IPhone OS environments? I understand when talking about theses environments we're actually talking about 3-4 different architectures (PPC, i386, Arm and the A4 Arm variant) so there may not be a single answer. Nevertheless does the general principle hold that in modern 32 bit / 64 bit systems using 1-2 byte variables that don't align with the machine's natural 4 byte words doesn't provide much of the efficiency we may expect. For instance, a plain old C-Array of 100,000 chars is smaller than the same 100,000 ints by a factor of four, but if during an enumeration, reading out each index involves a cast/boxing/unboxing of sorts, will we see overall lower 'performance' despite the saved memory overhead?

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• NPE annotation scenarios and static-analysis tools for Java

  - by alex2k8

  Here is a number of code snippets that can throw NullPointerException. 01: public void m1(@Nullable String text) { System.out.print(text.toLowerCase()); // <-- expect to be reported. } 02: private boolean _closed = false; public void m1(@Nullable String text) { if(_closed) return; System.out.print(text.toLowerCase()); // <-- expect to be reported. } 03: public void m1(@NotNull String text) { System.out.print(text.toLowerCase()); } public @Nullable String getText() { return "Some text"; } public void m2() { m1(getText()); // <-- expect to be reported. } Different people have access to different static-analysis tools. It would be nice to collect information, what tools are able to detect and report the issues, and what are failing. Also, if you have your own scenarious, please, publish them. Here my results FindBugs (1.3.9): 01: Parameter must be nonnull but is marked as nullable 02: NOT reported 03: NOT reported IntelliJ IDE 9.0.2 (Community edition): 01: Method invocation text.toLowerCase() may produce java.lang.NullPointerException 02: Method invocation text.toLowerCase() may produce java.lang.NullPointerException 03: Argument getText() might be null

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• Is this a hole in dynamic binding in C# 4?

  - by Galilyou

  I've seen a very interesting post on Fabio Maulo's blog. Here's the code and the bug if you don't want to jump to the url. I defined a new generic class like so: public class TableStorageInitializer<TTableEntity> where TTableEntity : class, new() { public void Initialize() { InitializeInstance(new TTableEntity()); } public void InitializeInstance(dynamic entity) { entity.PartitionKey = Guid.NewGuid().ToString(); entity.RowKey = Guid.NewGuid().ToString(); } } Note that InitializeInstance accepts one parameter, which is of type dynamic. Now to test this class, I defined another class that is nested inside my main Program class like so: class Program { static void Main(string[] args) { TableStorageInitializer<MyClass> x = new TableStorageInitializer<MyClass>(); x.Initialize(); } private class MyClass { public string PartitionKey { get; set; } public string RowKey { get; set; } public DateTime Timestamp { get; set; } } } Note: the inner class "MyClass" is declared private. Now if i run this code I get a "Microsoft.CSharp.RuntimeBinder.RuntimeBinderException" on the line "entity.PartitionKey = Guide.NewGuid().ToString()". The interesting part, though is that the message of the exception says "Object doesn't contain a definition for PartitionKey". Also note that if you changed the modifier of the nested class to public, the code will execute with no problems. So what do you guys think is really happening under the hood? Please refer to any documentation -of course if this is documented anywhere- that you may find?

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• Swipe left/right to push next/previous details view

  - by Youssef

  I am working on a ios application, using storyboard. I have a simple table view with rows. Each row has a "key" string to identify it. When the user clicks on a row I push the next view "DetailsViewController" and pass the "key" as a parameter in the prepareForSegue method. The data in the second view will change based on the "key" passed. In the "DetailsViewController" I want to add a swipe gesture, when the user swipes right, I want to push the next details view. It will be as if he clicked on the next row in the table view. So to rephrase, the user has 2 ways of switching between items: he can click the item in the table view and the details view will show, he can then go back and select another item. Or he can click on a row, and in the details view he can swipe left and right to see the previous/next item. i added the uigesture recognizer: UISwipeGestureRecognizer *recognizer; recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipe:)]; [recognizer setDirection:UISwipeGestureRecognizerDirectionRight]; [[self view] addGestureRecognizer:recognizer]; - (void) handleSwipe:(UISwipeGestureRecognizer *) sender { //I want to go to the next item in the tableview } I hope I was clear. Thank you.

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• OO - inheritance vs. decoration problem

  - by Karel J

  Hi all, I have an OOP-related question. I have an interface, say: class MyInterface { public int getValue(); } In my project, this interface is implemented by 7 implementations: class MyImplementation1 implements MyInterface { ... } ... class MyImplementation7 implements MyInterface { ... } These implementations are used by several different modules. For some modules, the behaviour of the MyInterface must be adjusted slightly. Let's that it must return the value of the implementator + 1 (for the sake of example). I solved this by creating a little decorator: class MyDifferentInterface implements MyInterface { private MyInterface i; public MyDifferentInterface(MyInterface i) { this.i = i; } public int getValue() { return i.getValue() + 1; } } This does the job. Here is my problem: one of the modules doesn't accept an MyInterface parameter, but MyImplementation4 directly. The reason for this is that this module needs specific behaviour of MyImplementation4, which are not covered by the interface MyInterface on itself. But, and here comes the difficulty, this module must also work on the modified version of MyImplementation4. That is, getValue() must return +1; What is the best way to solve this? I fail to come up with a solution which does not include lots of code duplicates. Please note that although the example above is pretty small and simple, the interface and the decorator is quite large and complicated. Thanks a lot all.

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• Facebook IFrame Application issues for certain users

  - by Kon

  We have a strange issue with running an Facebook IFrame application (using MVC 2). When I run my app and log into Facebook, I get to the application just fine. But when my coworker does it, she gets the following error: API Error Code: 100 API Error Description: Invalid parameter Error Message: Requires valid next URL. Typically this error is resolved by updating the "New Data Permissions" setting of the Facebook application. However, in this case it doesn't help. We've also tried logging in with our accounts from different computers and it seems that neither computer nor which one the MVC ASP.NET app is running from matters. The only difference is who is logged into Facebook. We've looked at our Facebook account settings, but couldn't find any obvious differences. We both have Developer access to the FB application and we both can edit its settings. However, only one of us can actually run the application without getting the above mentioned error message. Any idea what could be happening here?

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• What do I have to change in my PHP/CURL code to retrieve data from a https:// URL?

  - by Edward Tanguay

  I have a PHP file using CURL that accepts a Google Doc URL as a parameter, then returns the plain text of the Google Doc. It worked well until recently when apparently a redirect was added so that the http:// address redirects to the equivalent https:// address, as in this example: http://docs.google.com/View?id=dc7gj86r_20dn2csqg3 So I changed my code to access the https:// address, but it just returns blank. What do I have to change my CURL code so that I can get the HTML text from the https:// address? $url = filter_input(INPUT_GET, 'url',FILTER_SANITIZE_STRING); $validUrlPrefixes[] = "https://docs.google.com"; if(beginsWithOneOfThese($url, $validUrlPrefixes)) { $user_agent = 'Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3 (.NET CLR 3.5.30729)'; $ch = curl_init(); curl_setopt($ch, CURLOPT_COOKIEJAR, "/tmp/cookie"); curl_setopt($ch, CURLOPT_COOKIEFILE, "/tmp/cookie"); curl_setopt($ch, CURLOPT_URL, $url ); curl_setopt($ch, CURLOPT_FAILONERROR, 1); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 0); curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); curl_setopt($ch, CURLOPT_TIMEOUT, 15); curl_setopt($ch, CURLOPT_USERAGENT, $user_agent); curl_setopt($ch, CURLOPT_VERBOSE, 0); $rawData = curl_exec($ch); $rawData = cleanText($rawData); if(beginsWith($url, "https://docs.google.com")) { echo qstr::convertGoogleDocContentToText($rawData); die; } echo $rawData; die;

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• How can I pass a const array or a variable array to a function in C?

  - by CSharperWithJava

  I have a simple function Bar that uses a set of values from a data set that is passed in in the form of an Array of data structures. The data can come from two sources: a constant initialized array of default values, or a dynamically updated cache. The calling function determines which data is used and should be passed to Bar. Bar doesn't need to edit any of the data and in fact should never do so. How should I declare Bar's data parameter so that I can provide data from either set? union Foo { long _long; int _int; } static const Foo DEFAULTS[8] = {1,10,100,1000,10000,100000,1000000,10000000}; static Foo Cache[8] = {0}; void Bar(Foo* dataSet, int len);//example function prototype Note, this is C, NOT C++ if that makes a difference; Edit Oh, one more thing. When I use the example prototype I get a type qualifier mismatch warning, (because I'm passing a mutable reference to a const array?). What do I have to change for that?

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• C++ return a "NULL" object if search result not found

  - by aduric

  I'm pretty new to C++ so I tend to design with a lot of Java-isms while I'm learning. Anyway, in Java, if I had class with a 'search' method that would return an object T from a Collection< T that matched a specific parameter, I would return that object and if the object was not found in the collection, I would return a NULL. Then in my calling function I would just check if(T != NULL) { ... } In C++, I'm finding out that I can't return a NULL if the object doesn't exist. I just want to return an 'indicator' of type T that notifies the calling function that no object has been found. I don't want to throw an exception because it's not really an exceptional circumstance. class Node { .... Attr& getAttribute(const string& attribute_name) const { //search collection //if found at i return attributes[i]; //if not found return NULL; } private: vector<Attr> attributes; }

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• java 6 web services share domain specific classes between server and client

  - by user173446

  Hi all, Context: Considering below defined Engine class being parameter of some webservice method. As we have both server and client in java we may have some benefits (???) in sharing Engine class between server and client ( i.e we may put in a common jar file to be added to both client and server classpath ) Some benefits would be : we keep specific operations like 'brushEngine' in same place build is faster as we do not need in our case to generate java code for client classes but to use them from the server build) if we later change server implementation for 'brushEngine' this is reflected automatically in client . Questions: How to share below detailed Engine class using java 6 tools ( i.e wsimport , wsgen etc )? Is there other tools for java that can achieve this sharing ? Is sharing a case that java 6 web services support is missing ? Can this case be reduced to other web service usage patterns? Thanks. Code: public class Engine { private String engineData; public String getData(){ return data; } public setData(String value){ this.data = value; } public void brushEngine(){ engineData = "BrushedEngine"+engineData; } }

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• How to manage data access / preloading efficiently using web services in C# ?

  - by Amadeus45

  Hello all, Ok, this is very "generic" question. We currently have a SQL Server database for which we need to develop an application in ASP.NET with will contain all the business logic in C# Web Services. The thing is that, architecturally speaking, I'm not sure how to design the web service and the data management. There are many things to consider : We need have very rapid access to data. Right now, we have over a million "sales" and "purchases" record from which we need to often calculate and load the current stock for a given day according to a serie of parameter. I'm not sure how we should preload the data and keep the data in the Web Service. Doing a stock calculation within a SQL query will be very lengthy. They currently have a stock calculation application that preloads all sales and purchases for the day and afterwards calculate the stock on the code-side. We want to develop powerful reporting tools. We want to implement a "pivot table" but not sure how to implement it and have good performances. For the reasons above, I'm not sure how to design the data model. Anybody can give me any guidelines on how to start, or from their personnal experiences (what have you done in the past ?) I'm not sure if it's possible to make a bounty even though the question is new (I'd put 300 rep on it, since I really need something). If you know how, let me know. Thanks

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• SEO, ordering and duplication of content

  - by piquadrat

  I run a specialized news site and am trying to apply a little bit of SEO sauce to it. One of the most important things I hear is to avoid duplication of content. I've covered all the basics but I'm stuck with ordering of content. As an example, the archive of the site is orderable by date, views, and rating. Since we don't have that many news items, an archive page for a particular day has usually only a couple of items, so the following URLs all have the same content, albeit in different ordering: /news/archive/2010/05/16/ /news/archive/2010/05/16/?o=views /news/archive/2010/05/16/?o=rating Do search machines penalize this particular kind of duplication of content? And if yes, what's the best way to avoid said penalty? <link rel="canonical" />? Tell Google & Co. to ingore the o parameter? Marking the ordering links with nofollow? Only allow the indexation of the date-ordered archive sites through robots.txt (not sure if this is even possible)?

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• F# and statically checked union cases

  - by Johan Jonasson

  Soon me and my brother-in-arms Joel will release version 0.9 of Wing Beats. It's an internal DSL written in F#. With it you can generate XHTML. One of the sources of inspiration have been the XHTML.M module of the Ocsigen framework. I'm not used to the OCaml syntax, but I do understand XHTML.M somehow statically check if attributes and children of an element are of valid types. We have not been able to statically check the same thing in F#, and now I wonder if someone have any idea of how to do it? My first naive approach was to represent each element type in XHTML as a union case. But unfortunately you cannot statically restrict which cases are valid as parameter values, as in XHTML.M. Then I tried to use interfaces (each element type implements an interface for each valid parent) and type constraints, but I didn't manage to make it work without the use of explicit casting in a way that made the solution cumbersome to use. And it didn't feel like an elegant solution anyway. Today I've been looking at Code Contracts, but it seems to be incompatible with F# Interactive. When I hit alt + enter it freezes. Just to make my question clearer. Here is a super simple artificial example of the same problem: type Letter = | Vowel of string | Consonant of string let writeVowel = function | Vowel str -> sprintf "%s is a vowel" str I want writeVowel to only accept Vowels statically, and not as above, check it at runtime. How can we accomplish this? Does anyone have any idea? There must be a clever way of doing it. If not with union cases, maybe with interfaces? I've struggled with this, but am trapped in the box and can't think outside of it.

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• What should I do if i have a factory method which requires different parameters for different implem

  - by Sam Holder

  I have an interface, IMessage and a class which have several methods for creating different types of message like so: class MessageService { IMessage TypeAMessage(param 1, param 2) IMessage TypeBMessage(param 1, param 2, param 3, param 4) IMessage TypeCMessage(param 1, param 2, param 3) IMessage TypeDMessage(param 1) } I don't want this class to do all the work for creating these messages so it simply delegates to a MessageCreatorFactory which produces an IMessageCreator depending on the type given (an enumeration based on the type of the message TypeA, TypeB, TypeC etc) interface IMessageCreator { IMessage Create(MessageParams params); } So I have 4 implementations of IMessageCreator: TypeAMessageCreator, TypeBMessageCreator, TypeCMessageCreator, TypeDMessageCreator I ok with this except for the fact that because each type requires different parameters I have had to create a MessageParams object which contains 4 properties for the 4 different params, but only some of them are used in each IMessageCreator. Is there an alternative to this? One other thought I had was to have a param array as the parameter in the Create emthod, but this seems even worse as you don't have any idea what the params are. Or to create several overloads of Create in the interface and have some of them throw an exception if they are not suitable for that particular implementation (ie you called a method which needs more params, so you should have called one of the other overloads.) Does this seem ok? Is there a better solution?

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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