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• Does RVM "failover" to another ruby instance on error?

  - by JohnMetta

  Have a strange problem in that I have a Rake task that seems to be using multiple versions of Ruby. When one fails, it seems to try another one. Details MacBook running 10.6.5 rvm 1.1.0 Rubies: 1.8.7-p302, ree-1.8.7-2010.02, ruby-1.9.2-p0 Rake 0.8.7 Gem 1.3.7 Veewee (provisioning Virtual Machines using Opcode.com, Vagrant and Chef) I'm not entirely sure the specific details of the error matter, but since it might be an issue with Veewee itself. So, what I'm trying to do is build a new box base on a veewee definition. The command fails with an error about a missing method- but what's interesting is how it fails. Errors I managed to figure out that if I only have one Ruby installed with RVM, it just fails. If I have more than one Ruby install, it fails at the same place, but execution seems to continue in another interpreter. Here are two different clipped console outputs. I've clipped them for size. The full outputs of each error are available as a gist. One Ruby version installed Here is the command run when I only have a single version of Ruby (1.8.7) available in RVM boudica:veewee john$ rvm rake build['mettabox'] --trace rvm 1.1.0 by Wayne E. Seguin ([email protected]) [http://rvm.beginrescueend.com/] (in /Users/john/Work/veewee) ** Invoke build (first_time) ** Execute build … creating new harddrive rake aborted! undefined method `max_vdi_size' for #<VirtualBox::SystemProperties:0x102d6af80> /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/virtualbox-0.8.3/lib/virtualbox/abstract_model/dirty.rb:172:in `method_missing' <------ stacktraces cut ----------> /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/rake-0.8.7/bin/rake:31 /Users/john/.rvm/gems/ruby-1.8.7-p302@global/bin/rake:19:in `load' /Users/john/.rvm/gems/ruby-1.8.7-p302@global/bin/rake:19 Multiple Ruby Versions Here is the same command run with three versions of Ruby available in RVM. Prior to doing this, I used "rvm use 1.8.7." Again, I don't know how important the details of the specific errors are- what's interesting to me is that there are three separate errors- each with it's own stacktrace- and each in a different Ruby interpreter. Look at the bottom of each stacktrace and you'll see that they are all sourced from different interpreter locations- First ree-1.8.7, then ruby-1.8.7, then ruby-1.9.2: boudica:veewee john$ rvm rake build['mettabox'] --trace rvm 1.1.0 by Wayne E. Seguin ([email protected]) [http://rvm.beginrescueend.com/] (in /Users/john/Work/veewee) ** Invoke build (first_time) ** Execute build … creating new harddrive rake aborted! undefined method `max_vdi_size' for #<VirtualBox::SystemProperties:0x1059dd608> /Users/john/.rvm/gems/ree-1.8.7-2010.02/gems/virtualbox-0.8.3/lib/virtualbox/abstract_model/dirty.rb:172:in `method_missing' … /Users/john/.rvm/gems/ree-1.8.7-2010.02/gems/rake-0.8.7/bin/rake:31 /Users/john/.rvm/gems/ree-1.8.7-2010.02@global/bin/rake:19:in `load' /Users/john/.rvm/gems/ree-1.8.7-2010.02@global/bin/rake:19 (in /Users/john/Work/veewee) ** Invoke build (first_time) ** Execute build isofile ubuntu-10.04.1-server-amd64.iso is available ["a1b857f92eecaf9f0a31ecfc39dee906", "30b5c6fdddbfe7b397fe506400be698d"] [] Last good state: -1 Current step: 0 last good state -1 destroying machine+disks (re-)executing step 0-initial-a1b857f92eecaf9f0a31ecfc39dee906 VBoxManage: error: Machine settings file '/Users/john/VirtualBox VMs/mettabox/mettabox.vbox' already exists VBoxManage: error: Details: code VBOX_E_FILE_ERROR (0x80bb0004), component Machine, interface IMachine, callee nsISupports Context: "CreateMachine(bstrSettingsFile.raw(), name.raw(), osTypeId.raw(), Guid(id).toUtf16().raw(), FALSE , machine.asOutParam())" at line 247 of file VBoxManageMisc.cpp rake aborted! undefined method `memory_size=' for nil:NilClass /Users/john/Work/veewee/lib/veewee/session.rb:303:in `create_vm' /Users/john/Work/veewee/lib/veewee/session.rb:166:in `build' /Users/john/Work/veewee/lib/veewee/session.rb:560:in `transaction' /Users/john/Work/veewee/lib/veewee/session.rb:163:in `build' /Users/john/Work/veewee/Rakefile:87 /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/rake-0.8.7/lib/rake.rb:636:in `call' /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/rake-0.8.7/lib/rake.rb:636:in `execute' /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/rake-0.8.7/lib/rake.rb:631:in `each' … /Users/john/.rvm/gems/ruby-1.8.7-p302/gems/rake-0.8.7/bin/rake:31 /Users/john/.rvm/gems/ruby-1.8.7-p302@global/bin/rake:19:in `load' /Users/john/.rvm/gems/ruby-1.8.7-p302@global/bin/rake:19 (in /Users/john/Work/veewee) ** Invoke build (first_time) ** Execute build isofile ubuntu-10.04.1-server-amd64.iso is available ["a9c4ab3257e1da3479c984eae9905c2a", "30b5c6fdddbfe7b397fe506400be698d"] [] Last good state: -1 Current step: 0 last good state -1 (re-)executing step 0-initial-a9c4ab3257e1da3479c984eae9905c2a VBoxManage: error: Machine settings file '/Users/john/VirtualBox VMs/mettabox/mettabox.vbox' already exists VBoxManage: error: Details: code VBOX_E_FILE_ERROR (0x80bb0004), component Machine, interface IMachine, callee nsISupports Context: "CreateMachine(bstrSettingsFile.raw(), name.raw(), osTypeId.raw(), Guid(id).toUtf16().raw(), FALSE , machine.asOutParam())" at line 247 of file VBoxManageMisc.cpp rake aborted! undefined method `memory_size=' for nil:NilClass /Users/john/Work/veewee/lib/veewee/session.rb:303:in `create_vm' /Users/john/Work/veewee/lib/veewee/session.rb:166:in `block in build' /Users/john/Work/veewee/lib/veewee/session.rb:560:in `transaction' /Users/john/Work/veewee/lib/veewee/session.rb:163:in `build' /Users/john/Work/veewee/Rakefile:87:in `block in <top (required)>' /Users/john/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rake.rb:634:in `call' /Users/john/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rake.rb:634:in `block in execute' … /Users/john/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rake.rb:2013:in `top_level' /Users/john/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rake.rb:1992:in `run' /Users/john/.rvm/rubies/ruby-1.9.2-p0/bin/rake:35:in `<main>' It isn't until we reach the last installed version of Ruby that execution halts. Discussion Does anyone have any idea what's going on here? Has anyone seen this "failover"-like behavior before? It seems strange to me that the first exception would not halt execution as it did with one interpreter, but I wonder if there are things happening when RVM is installed that we Ruby developers are not considering.

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• How do I create interface methods using .tlb types in VS C++?

  - by Steven

  Background: The .TLB file contains interfaces written in language 'X'. I don't have .h, .idl, .tlh, or any other header files - just the .TLB file. Language 'X' does not export compatible .h, .idl, etc. I use the VS wizard to add an ATL simple object to my ATL project. I want to add a method to the interface of my simple ATL object that uses one of the .TLB defined types for a parameter. // Something like the following in the .idl file: interface ISomeInterface : IUnknown { HRESULT SomeMethod([in] ITypeFromTLB* aVal); // ITypeFromTLB declared in .TLB file. }; How can I do this? I'm hoping for a wizard, or a line in the .idl interface declaration that would bring in the .tlb information. midl's include (no .tlb), import (no tlb), and importlib (library only) don't seem to provide a solution (I need proxy/stub to be working, so I cannot put this inside the library declaration with the importlib command). Thanks.

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• How do I free SQLServerCE's COM instance from the current running process?

  - by David Thornley

  It's been a while since I touched COM so be nice ;) This is under WindowsCE 5.0 with SQLServerCE 2.0. After calling this to load SQLServerCE 2.0 : - IDBInitialize *pIDBInitialize = NULL; CoCreateInstance(CLSID_SQLSERVERCE_2_0, NULL, CLSCTX_INPROC_SERVER, IID_IDBInitialize, (void**)&pIDBInitialize); Module load occurs for SSCE20.dll which obviously loads the SQLServerCE engine into the process space. What I don't understand is if I do this immediately after :- pIDBInitialize->Release(); I don't see a dll module unload, so that SSCE20.dll (and friends) are still loaded into my process. Now I tried CoFreeUnusedLibraries() which I figure forces COM to purge any unused libraries, but it doesn't seem to do the trick. At runtime I want to be able to completely unload the SQLServerCE 2.0 dll from the process to streamline an upgrade to 3.5SP1. I suspect this has something to do with the shared dll model that Microsoft use under WindowsCE... but, I might be wrong :) Thanks in advance, David.

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• 3 methods for adding a "Product" through Entity Framework. What's the difference?

  - by Kohan

  Reading this MSDN article titled "Working with ObjectSet (Entity Framework)" It shows two examples on how to add a Product.. one for 3.5 and another for 4.0. http://msdn.microsoft.com/en-us/library/ee473442.aspx Through my lack of knowledge I am possibly completely missing something here, but i never added a Product like this: //In .NET Framework 3.5 SP1, use the following code: (ObjectQuery) using (AdventureWorksEntities context = new AdventureWorksEntities()) { // Add the new object to the context. context.AddObject("Products", newProduct); } //New in .NET Framework 4, use the following code: (ObjectSet) using (AdventureWorksEntities context = new AdventureWorksEntities()) { // Add the new object to the context. context.Products.AddObject(newProduct); } I would not have done it either way and just used: // (My familiar way) using (AdventureWorksEntities context = new AdventureWorksEntities()) { // Add the new object to the context. context.AddToProducts(newProduct); } What's the difference between these three ways? Is "My way" just another way of using an ObjectQuery? Thanks, Kohan

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• How can i do this using a Python Regex?

  - by uberjumper

  I am trying to properly extract methods definitions that are generated by comtypes for Com Interfaces using a regex. Furthermore some of them are blank which causes even more problems for me. Basically i have this: IXMLSerializerAlt._methods_ = [ COMMETHOD([helpstring(u'Loads an object from an XML string.')], HRESULT, 'LoadFromString', ( ['in'], BSTR, 'XML' ), ( ['in'], BSTR, 'TypeName' ), ( ['in'], BSTR, 'TypeNamespaceURI' ), ( ['retval', 'out'], POINTER(POINTER(IUnknown)), 'obj' )), ] class EnvironmentManager(CoClass): u'Singleton object that manages different environments (collections of configuration information).' _reg_clsid_ = GUID('{8A626D49-5F5E-47D9-9463-0B802E9C4167}') _idlflags_ = [] _typelib_path_ = typelib_path _reg_typelib_ = ('{5E1F7BC3-67C5-4AEE-8EC6-C4B73AAC42ED}', 1, 0) INumberFormat._methods_ = [ ] I want to extract both the IXMLSerializerAlt and INumberFormat methods definitions however i cant figure out a proper regex. E.g. for IXMLSerializer i want to extract this: IXMLSerializerAlt._methods_ = [ COMMETHOD([helpstring(u'Loads an object from an XML string.')], HRESULT, 'LoadFromString', ( ['in'], BSTR, 'XML' ), ( ['in'], BSTR, 'TypeName' ), ( ['in'], BSTR, 'TypeNamespaceURI' ), ( ['retval', 'out'], POINTER(POINTER(IUnknown)), 'obj' )), ] This regex in my mind this should work: ^\w+\._methods_\s=\s\[$ (^.+$)* ^]$ Im checking my regex's using kodos however i cannot figure out a way to make this work.

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• What are some methods to debug Javascript inside of a UIWebView?

  - by bpapa

  I'm trying to figure out why something with Javascript isn't working inside of a UIWebView. To my knowledge, there is no way to set a breakpoint inside of XCode for a js file. No problemo, I'll just go back to 2004 and use alert statemen-- oh wait they don't seem to work inside of a UIWebView either! The only thing I could think of is by exporting my HTML And JS files to my desktop and then just doing my debugging inside of Safari. And that works! But of course, the bug I'm fighting with in the UIWebView doesn't occur in Safari. Are there any other ways for debugging inside of a UIWebView, or any tricks that I can use akin to using the old-school alert method?

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• Should all public methods of an API be documented?

  - by cynicalman

  When writing "library" type classes, is it better practice to always write markup documentation (i.e. javadoc) in java or assume that the code can be "self-documenting"? For example, given the following method stub: /** * Copies all readable bytes from the provided input stream to the provided output * stream. The output stream will be flushed, but neither stream will be closed. * * @param inStream an InputStream from which to read bytes. * @param outStream an OutputStream to which to copy the read bytes. * @throws IOException if there are any errors reading or writing. */ public void copyStream(InputStream inStream, OutputStream outStream) throws IOException { // copy the stream } The javadoc seems to be self-evident, and noise that just needs to be updated if the funcion is changed at all. But the sentence about flushing and not closing the stream could be valuable. So, when writing a library, is it best to: a) always document b) document anything that isn't obvious c) never document (code should speak for itself!) I usually use b), myself (since the code can be self-documenting otherwise)...

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• Any way to identify a redirect when using jQuery's $.ajax() or $.getScript() methods?

  - by Bungle

  Within my company's online application, we've set up a JSONP-based API that returns some data that is used by a bookmarklet I'm developing. Here is a quick test page I set up that hits the API URL using jQuery's $.ajax() method: http://troy.onespot.com/static/3915/index.html If you look at the requests using Firebug's "Net" tab (or the like), you'll see that what's happening is that the URL is requested successfully, but since our app redirects any unauthorized users to a login page, the login page is also requested by the browser and seemingly interpreted as JavaScript. This inevitably causes an exception since the login page is HTML, not JavaScript. Basically, I'm looking for any sort of hook to determine when the request results in a redirect - some way to determine if the URL resolved to a JSONP response (which will execute a method I've predefined in the bookmarklet script) or if it resulted in a redirect. I tried wrapping the $.ajax() method in a try {} catch(e) {} block, but that doesn't trap the exception, I'm assuming because the requests were successful, just not the parsing of the login page as JavaScript. Is there anywhere I could use a try {} catch(e) {} block, or any property of $.ajax() that might allow me to hone in on the exception or otherwise determine that I've been redirected? I actually doubt this is possible, since $.getScript() (or the equivalent setup of $.ajax()) just loads a script dynamically, and can't inspect the response headers since it's cross-domain and not truly AJAX: http://api.jquery.com/jQuery.getScript/ My alternative would be to just fire off the $.ajax() for a period of time until I either get the JSONP callback or don't, and in the latter case, assume the user is not logged in and prompt them to do so. I don't like that method, though, since it would result in a lot of unnecessary requests to the app server, and would also pile up the JavaScript exceptions in the meantime. Thanks for any suggestions!

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• Why can't I call methods within a class that explicitly implements an interface?

  - by tyrone302

  Here's the story. I created and interface, IVehicle. I explicitly implemented the interface in my class, Vehicle.cs. Here is my interface: Interface IVehicle { int getWheel(); } here is my class: class Vehicle: IVehicle { public int IVehicle.getWheel() { return wheel; } public void printWheel() { Console.WriteLine(getWheel()); } } Notice that "getWheel()" is explicitly implemented. Now, when I try to call that method within my Vehicle class, I receive an error indicating that getWheel() does not exist in the current context. Can someone help me understand what I am doing wrong?

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• good books on numerical computation with C

  - by yCalleecharan

  Hi, I've read the post "What is the best book on numerical methods?" and I wish to ask more or less the same question but in relation to C programming. Most of the time, C programming books on numerical methods are just another version of the author's previous Fortran book on the same subject. I've seen Applied numerical methods in C by Nakamura, Shoichiro and the C codes are not good programming practice. I've heard bad comments about Numerical Recipes by Press. Do you know good books on C that discusses numerical methods. It's seem better for me to ask about good books on C discussing numerical methods than rather asking books on numerical methods that discusses C. I've heard about Numerical Algorithms with C by Giesela Engeln-Müllges and A Numerical Library in C for Scientists and Engineers bu Lau but haven't read them. Good books will always have algorithms implemented in the programming language in a smart way. Thanks a lot...

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• How can I determine in silverlight code where the silverlight instance is running?

  - by Edward Tanguay

  I have a silverlight app. When I develop I have it pick up its data from a local URL: http://localhost/theapp/data/... however, when it is online, I want it to pick up its data from an online URL: http://www.tanguay.info/... Currently I have a variable which I switch before I compile and upload: bool silverlightAppIsLive = true; which I use to determine whether or not to get data from the first or second URL above. Is there a way for me to determine this automatically in code without setting the variable manually?

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• How to make a model instance read-only after saving it once?

  - by Ryszard Szopa

  One of the functionalities in a Django project I am writing is sending a newsletter. I have a model, Newsletter and a function, send_newsletter, which I have registered to listen to Newsletter's post_save signal. When the newsletter object is saved via the admin interface, send_newsletter checks if created is True, and if yes it actually sends the mail. However, it doesn't make much sense to edit a newsletter that has already been sent, for the obvious reasons. Is there a way of making the Newsletter object read-only once it has been saved? Edit: I know I can override the save method of the object to raise an error or do nothin if the object existed. However, I don't see the point of doing that. As for the former, I don't know where to catch that error and how to communicate the user the fact that the object wasn't saved. As for the latter, giving the user false feedback (the admin interface saying that the save succeded) doesn't seem like a Good Thing. What I really want is allow the user to use the Admin interface to write the newsletter and send it, and then browse the newsletters that have already been sent. I would like the admin interface to show the data for sent newsletters in an non-editable input box, without the "Save" button. Alternatively I would like the "Save" button to be inactive.

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• How does Java's Hello World work without an object instance?

  - by vipinsahu

  Hi, I'm a newbie to Java and I'm confused about something: In the simple hello world program in Java, no object is created so how does the class work in the following example? public class HelloWorld { public static void main (String args[]) { System.out.println ("Hello World!"); } }

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• Should I supress CA1062: Validate arguments of public methods?

  - by brickner

  I've recently upgraded my project to Visual Studio 2010 from Visual Studio 2008. In Visual Studio 2008, this Code Analysis rule doesn't exist. Now I'm not sure if I should use this rule or not. I'm building an open source library so it seems important to keep people safe from doing mistakes. However, if all I'm going to do is throw ArgumentNullException when the parameter is null, it seems like writing useless code since ArgumentNullException will be thrown even if I won't write that code. Should I remove that rule or fix the violations?

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• How do I imply code contracts of chained methods to avoid superfluous checks while chaining?

  - by Sandor Drieënhuizen

  I'm using Code Contracts in C# 4.0. I'm applying the usual static method chaining to simulate optional parameters (I know C# 4.0 supports optional parameters but I really don't want to use them). The thing is that my contract requirements are executed twice (or possibly the number of chained overloads I'd implement) if I call the Init(string , string[]) method -- an obvious effect from the sample source code below. This can be expensive, especially due to relatively expensive requirements like the File.Exists I use. public static void Init(string configurationPath, string[] mappingAssemblies) { // The static contract checker 'makes' me put these here as well as // in the overload below. Contract.Requires<ArgumentNullException>(configurationPath != null, "configurationPath"); Contract.Requires<ArgumentException>(configurationPath.Length > 0, "configurationPath is an empty string."); Contract.Requires<FileNotFoundException>(File.Exists(configurationPath), configurationPath); Contract.Requires<ArgumentNullException>(mappingAssemblies != null, "mappingAssemblies"); Contract.ForAll<string>(mappingAssemblies, (n) => File.Exists(n)); Init(configurationPath, mappingAssemblies, null); } public static void Init(string configurationPath, string[] mappingAssemblies, string optionalArgument) { // This is the main implementation of Init and all calls to chained // overloads end up here. Contract.Requires<ArgumentNullException>(configurationPath != null, "configurationPath"); Contract.Requires<ArgumentException>(configurationPath.Length > 0, "configurationPath is an empty string."); Contract.Requires<FileNotFoundException>(File.Exists(configurationPath), configurationPath); Contract.Requires<ArgumentNullException>(mappingAssemblies != null, "mappingAssemblies"); Contract.ForAll<string>(mappingAssemblies, (n) => File.Exists(n)); //... } If however, I remove the requirements from that method, the static checker complains that the requirements of the Init(string, string[], string) overload are not met. I reckon that the static checker doesn't understand that there requirements of the Init(string, string[], string) overload implicitly apply to the Init(string, string[]) method as well; something that would be perfectly deductable from the code IMO. This is the situation I would like to achieve: public static void Init(string configurationPath, string[] mappingAssemblies) { // I don't want to repeat the requirements here because they will always // be checked in the overload called here. Init(configurationPath, mappingAssemblies, null); } public static void Init(string configurationPath, string[] mappingAssemblies, string optionalArgument) { // This is the main implementation of Init and all calls to chained // overloads end up here. Contract.Requires<ArgumentNullException>(configurationPath != null, "configurationPath"); Contract.Requires<ArgumentException>(configurationPath.Length > 0, "configurationPath is an empty string."); Contract.Requires<FileNotFoundException>(File.Exists(configurationPath), configurationPath); Contract.Requires<ArgumentNullException>(mappingAssemblies != null, "mappingAssemblies"); Contract.ForAll<string>(mappingAssemblies, (n) => File.Exists(n)); //... } So, my question is this: is there a way to have the requirements of Init(string, string[], string) implicitly apply to Init(string, string[]) automatically?

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• TimeZoneInfo - why can't i seem to create an instance of it?

  - by Kravlin

  I'm trying to use the EWS API to access an Exchange server from a console program i'm writing. I've specified the type of exchange server i'm connecting to but when I try to execute the code i have, it gives me Error 1 The type 'System.TimeZoneInfo' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. C:\Documents and Settings\jsorensen\My Documents\Visual Studio 2005\Projects\ConsoleApplication2\ConsoleApplication2\Program.cs 26 13 ConsoleApplication2 Does Microsoft Visual Studio Academic Edition not support TimeZoneInfo or is the version of .Net that XP can have not up-to date enough to work with the EWS API? I'm moderately new to programming in C# so some of the stuff is still confusing. Thanks.

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• How can I find out if an instance is a MarshalByRef proxy?

  - by Will

  I know there's a way, I know I've done it (a long time) before, but I can't remember or find out how to do it!!! var otherDomain = AppDomain.Create("Lol my memory sucks"); var myRemotableType = typeof(MyTypeThatExtendsMBRO); var proxy = otherDomain .CreateInstanceAndUnwrap( type.Assembly.FullName, type.FullName); // how do you do this next step??? bool isProxy = IsYouIsOrIsYouAintAProxy(proxy);

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• How do I set values for a class without using any setter methods?

  - by fari

  Please can anyone help me public class KalaGameState implements Cloneable { // your code goes here public KalaGameState(int startingStones) throws InvalidStartingStonesException { // your code goes here } public int getTurn() { // your code goes here } public int getKala(int playerNum) throws IllegalPlayerNumException { // your code goes here } public int getNumStones(int sidePitNum) throws IllegalSidePitNumException { // your code goes here } public int getNumStones(int playerNum, int sidePitNum) throws IllegalPlayerNumException, IllegalSidePitNumException { // your code goes here } public int getScore(int playerNum) throws IllegalPlayerNumException { // your code goes here } private int getSidePitArrayIndex(int sidePitNum) throws IllegalSidePitNumException { // your code goes here } public boolean gameOver() { // your code goes here } public void makeMove(int sidePitNum) throws IllegalSidePitNumException, IllegalMoveException { // your code goes here } }

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• When does invoking a member function on a null instance result in undefined behavior?

  - by GMan

  This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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• Is there a way to create a new instance for IRequestDictionary and IStringList on .NET?

  - by Ronie

  We are working on a C# DLL that stores the values of a Classic ASP Session. Everything is okay but some QueryStrings being stored in Session. Problem is: we are able to read the QueryString from the DLL using IRequestDictionary and IStringList, but we can't find a way to recreate them the next time a page ask for them. We have stored all information necessary to recreate them. So, the question is: Is it possible to instantiate and set their values back? Is there any other option?

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• mvvm-light: Should we merge Cleanup methods in locator?

  - by mark smith

  Hi there, when creating a new ViewModel within the locator class using the snippet it creates a Cleanup Method but there is already one available from the Main so hence an error.... Should we merge them all?? Or should we be renaming the method to Cleanup[Name of viewmodel] for example. I am a little confused here Another question i would like to ask is regards to the naming conventions. I tried to follow the naming convention used with "MAIN"... hence i have CreateLogin, ClearLogin, Login (non static property for binding) etc etc.. Would it not be better to use CreateLoginViewModel, ClearLoginViewModel etc?? Just curious Thanks

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• How do people prove the correctness of Computer Vision methods?

  - by solvingPuzzles

  I'd like to pose a few abstract questions about computer vision research. I haven't quite been able to answer these questions by searching the web and reading papers. How does someone know whether a computer vision algorithm is correct? How do we define "correct" in the context of computer vision? Do formal proofs play a role in understanding the correctness of computer vision algorithms? A bit of background: I'm about to start my PhD in Computer Science. I enjoy designing fast parallel algorithms and proving the correctness of these algorithms. I've also used OpenCV from some class projects, though I don't have much formal training in computer vision. I've been approached by a potential thesis advisor who works on designing faster and more scalable algorithms for computer vision (e.g. fast image segmentation). I'm trying to understand the common practices in solving computer vision problems.

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• How can I call VC# webservice methods without ArgumentException?

  - by Zarius

  Currently, I'm trying to write a small tray application that will show the status and provide control of a server-side application exposed over webservice. The webservice only has 3 operations: start, stop and status. When I call any of these operations in code, they throw an ArgumentException citing "An item with the same key has already been added". I am compiling the webservice on Visual C# Express 2008, and .NET 3.5. The Code: private TelnetConnClient Conn { get { return new TelnetConnClient(); } } private bool Connected //call webservice operations { get { return Conn.Status(); } set { if(value) Conn.Start(); else Conn.Stop(); } } The Stacktrace: A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at System.ServiceModel.TransactionFlowAttribute.ApplyBehavior(OperationDescription description, BindingParameterCollection parameters) at System.ServiceModel.TransactionFlowAttribute.System.ServiceModel.Description.IOperationBehavior.AddBindingParameters(OperationDescription description, BindingParameterCollection parameters) at System.ServiceModel.Description.DispatcherBuilder.AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection parameters) at System.ServiceModel.Description.DispatcherBuilder.BuildProxyBehavior(ServiceEndpoint serviceEndpoint, BindingParameterCollection& parameters) at System.ServiceModel.Channels.ServiceChannelFactory.BuildChannelFactory(ServiceEndpoint serviceEndpoint) at System.ServiceModel.ChannelFactory.CreateFactory() at System.ServiceModel.ChannelFactory.OnOpening() at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.ChannelFactory.EnsureOpened() at System.ServiceModel.ChannelFactory`1.CreateChannel(EndpointAddress address, Uri via) at System.ServiceModel.ChannelFactory`1.CreateChannel() at System.ServiceModel.ClientBase`1.CreateChannel() at System.ServiceModel.ClientBase`1.CreateChannelInternal() at System.ServiceModel.ClientBase`1.get_Channel() at KordiaConnect.ferries.TelnetConnClient.Start() in C:\My Dropbox\Coding\RTF\KordiaConnect\KordiaConnect\Service References\ferries\Reference.cs:line 86 at coldshark.ferries.Main.set_Connected(Boolean value) in C:\My Dropbox\Coding\RTF\KordiaConnect\KordiaConnect\Main.cs:line 22 at coldshark.ferries.Main.<.ctor>b__0(Object sender, EventArgs e) in C:\My Dropbox\Coding\RTF\KordiaConnect\KordiaConnect\Main.cs:line 43 at System.Windows.Forms.NotifyIcon.OnClick(EventArgs e) at System.Windows.Forms.NotifyIcon.WmMouseUp(Message& m, MouseButtons button) at System.Windows.Forms.NotifyIcon.WndProc(Message& msg) at System.Windows.Forms.NotifyIcon.NotifyIconNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.PeekMessage(MSG& msg, HandleRef hwnd, Int32 msgMin, Int32 msgMax, Int32 remove) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run() at coldshark.ferries.Main..ctor() in C:\My Dropbox\Coding\RTF\KordiaConnect\KordiaConnect\Main.cs:line 55 I can just call the webservice from the web interface, but this application will give me a handy status notification icon, and I'd really love to know why the out-of-the-box auto-generated code fails for no particular reason.

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• How could I refactor this into more manageable methods?

  - by ChaosPandion

  private static JsonStructure Parse(string jsonText, bool throwException) { var result = default(JsonStructure); var structureStack = new Stack<JsonStructure>(); var keyStack = new Stack<string>(); var current = default(JsonStructure); var currentState = ParserState.Begin; var invalidToken = false; var key = default(string); var value = default(object); foreach (var token in Lexer.Tokenize(jsonText)) { switch (currentState) { case ParserState.Begin: switch (token.Type) { case TokenType.OpenBrace: currentState = ParserState.ObjectKey; current = result = new JsonObject(); break; case TokenType.OpenBracket: currentState = ParserState.ArrayValue; current = result = new JsonArray(); break; default: invalidToken = true; break; } break; case ParserState.ObjectKey: switch (token.Type) { case TokenType.StringLiteral: currentState = ParserState.ColonSeperator; key = (string)token.Value; break; default: invalidToken = true; break; } break; case ParserState.ColonSeperator: switch (token.Type) { case TokenType.Colon: currentState = ParserState.ObjectValue; break; default: invalidToken = true; break; } break; case ParserState.ObjectValue: case ParserState.ArrayValue: switch (token.Type) { case TokenType.NumberLiteral: case TokenType.StringLiteral: case TokenType.BooleanLiteral: case TokenType.NullLiteral: currentState = ParserState.ItemEnd; value = token.Value; break; case TokenType.OpenBrace: structureStack.Push(current); keyStack.Push(key); currentState = ParserState.ObjectKey; current = new JsonObject(); break; case TokenType.OpenBracket: structureStack.Push(current); currentState = ParserState.ArrayValue; current = new JsonArray(); break; default: invalidToken = true; break; } break; case ParserState.ItemEnd: var jsonObject = (current as JsonObject); if (jsonObject != null) { jsonObject.Add(key, value); currentState = ParserState.ObjectKey; } var jsonArray = (current as JsonArray); if (jsonArray != null) { jsonArray.Add(value); currentState = ParserState.ArrayValue; } switch (token.Type) { case TokenType.CloseBrace: case TokenType.CloseBracket: currentState = ParserState.End; break; case TokenType.Comma: break; default: invalidToken = true; break; } break; case ParserState.End: switch (token.Type) { case TokenType.CloseBrace: case TokenType.CloseBracket: case TokenType.Comma: var previous = structureStack.Pop(); var previousJsonObject = (previous as JsonObject); if (previousJsonObject != null) { currentState = ParserState.ObjectKey; previousJsonObject.Add(keyStack.Pop(), current); } var previousJsonArray = (previous as JsonArray); if (previousJsonArray != null) { currentState = ParserState.ArrayValue; previousJsonArray.Add(current); } current = previous; if (token.Type != TokenType.Comma) { currentState = ParserState.End; } break; default: invalidToken = true; break; } break; default: break; } if (invalidToken) { if (throwException) { throw new JsonException(token); } return null; } } return result; }

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• how to use single instance of AVAudioPlayer for playing multiple songs?

  - by Abhijeet

  I want to play multiple songs with single object of AVAudioplayer, I put songs in table row , when user tap on row player view is open but when user go back in other row in table player play both songs simanteniosly . what I Can do to fix this?

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