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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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  • Categories & singelton in cocoa

    - by Nava Carmon
    Hi, I have a SingletonClass, which has only one instance. I want to expand it and add to it a category (MoreFeatures). I created a source SingletonClass+MoreFeatures, which interface/implementation looks like that: @interface SingletonClass (MoreFeatures) - (void) feature; @end @implementation SingletonClass (MoreFeatures) - (void) feature() { } @end When I created my SingletonClass i followed the Apple's example of Singleton implementation in cocoa. This singleton resides in a project B, which is a dependency of a bigger project A. I can call for [[SingletonClass sharedInstance] foo] from a source in project A and it works in case that function foo is located in SingletonClass interface/implementation. When I try to call [[SingletonClass sharedInstance] feature] from a source in project A, I get a crash, which says that there is no method feature for class SingletonClass... Why it happens? Thanks a lot, Nava EDIT: The crash happens in a runtime. The category file source resides in project B along with a SingletonClass

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  • Compiler doesn't find methods from base class

    - by Paul
    I am having a problem with my virtual methods in a derived class. Here are my (simplified) C++ classes. class Base virtual method accept( MyVisitor1* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor3* v ) { /*implementation is here*/ }; class DerivedClass virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; The following use causes VS 2005 to give: "error C2664: 'DerivedClass::accept' : cannot convert parameter 1 from 'Visitor1*' to 'Visitor2 *'". DerivedClass c; MyVisitor1 v1; c.accept(v1); I was expecting the compiler to find and call Base::accept(MyVisitor1) for my DerivedClass as well. Obviously this is not working, but I don't understand why. Any ideas? Thanks, Paul

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  • Inject same DataContext instance across several types with Unity

    - by Sergejus
    Suppose I have IRepository interface and its implementation SqlRepository that takes as an argument LINQ to SQL DataContext. Suppose as well that I have IService interface and its implementation Services that takes three IRepository, IRepository and IRepository. Demo code is below: public interface IRepository<T> { } public class SqlRepository<T> : IRepository<T> { public SqlRepository(DataContext dc) { ... } } public interface IService<T> { } public class Service<T,T1,T2,T3> : IService<T> { public Service(IRepository<T1> r1, IRepository<T2>, IRepository<T3>) { ... } } Is it any way while creating Service class to inject all three repositories with the same DataContext?

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  • Silly Objective-C inheritance problem when using property

    - by Ben Packard
    I've been scratching my head with this for a couple of hours - I haven't used inheritance much. Here I have set up a simple Test B class that inherits from Test A, where an ivar is declared. But I get the compilation error that the variable is undeclared. This only happens when I add the property and synthesize declarations - works fine without them. TestA Header: #import <Cocoa/Cocoa.h> @interface TestA : NSObject { NSString *testString; } @end TestA Implementation is empty: #import "TestA.h" @implementation TestA @end TestB Header: #import <Cocoa/Cocoa.h> #import "TestA.h" @interface TestB : TestA { } @property NSString *testProp; @end TestB Implementation (Error - 'testString' is undeclared) #import "TestB.h" @implementation TestB @synthesize testProp; - (void)testing{ NSLog(@"test ivar is %@", testString); } @end

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  • No Internet access while being connected to VPN using Cisco VPN Client 5.

    - by szeldon
    Hi, I have an access to corporate VPN using Cisco VPN Client 5.0.00:0340, but when I'm connected to it, I don't have an Internet access. I'm using Windows XP SP3. As it was suggested here http://forums.speedguide.net/showthread.php?t=209167 , I tried to enable "Allow local LAN Access" but it doesn't work. I also tried a second solution - deleting entry using "route" command, but it didn't help. I used "route delete 192.168.100.222". It's a third day of my attempts to solve this issue and I don't have an idea what else to do. I'm not very experienced in VPN stuff, but I know something about networking. Basing on my knowledge, I think that it's theoretically possible to achieve Internet access using my local network and only corporate stuff to be routed using VPN connection. I think that theoretically this should look like this: every IP being inside by corporation - VPN interface IP every other IP - my ethernet interface I've tried many possibilities of how to change those routes, but neither of them work. I'd really appreciate any help. My route configuration before connecting to VPN: =========================================================================== Interface List 0x1 ........................... MS TCP Loopback interface 0x2 ...00 c0 a8 de 79 01 ...... Atheros AR5006EG Wireless Network Adapter - Teefer2 Miniport 0x10005 ...02 00 4c 4f 4f 50 ...... Microsoft Loopback Card 0x160003 ...00 17 42 31 0e 16 ...... Marvell Yukon 88E8055 PCI-E Gigabit Ethernet Controller - Teefer2 Miniport =========================================================================== =========================================================================== Active routes: Network Destination Netmask Gateway Interface Metrics 0.0.0.0 0.0.0.0 192.168.101.254 192.168.100.222 10 10.0.0.0 255.255.255.0 10.0.0.10 10.0.0.10 30 10.0.0.10 255.255.255.255 127.0.0.1 127.0.0.1 30 10.255.255.255 255.255.255.255 10.0.0.10 10.0.0.10 30 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 192.168.100.0 255.255.254.0 192.168.100.222 192.168.100.222 1 192.168.100.222 255.255.255.255 127.0.0.1 127.0.0.1 1 192.168.100.255 255.255.255.255 192.168.100.222 192.168.100.222 1 224.0.0.0 240.0.0.0 10.0.0.10 10.0.0.10 3 224.0.0.0 240.0.0.0 192.168.100.222 192.168.100.222 1 255.255.255.255 255.255.255.255 10.0.0.10 10.0.0.10 1 255.255.255.255 255.255.255.255 192.168.100.222 192.168.100.222 1 255.255.255.255 255.255.255.255 192.168.100.222 2 1 Default gateway: 192.168.101.254. =========================================================================== My route configuration after connection to VPN: =========================================================================== Interface List 0x1 ........................... MS TCP Loopback interface 0x2 ...00 c0 a8 de 79 01 ...... Atheros AR5006EG Wireless Network Adapter - Teefer2 Miniport 0x10005 ...02 00 4c 4f 4f 50 ...... Microsoft Loopback Card 0x160003 ...00 17 42 31 0e 16 ...... Marvell Yukon 88E8055 PCI-E Gigabit Ethernet Controller - Teefer2 Miniport 0x170006 ...00 05 9a 3c 78 00 ...... Cisco Systems VPN Adapter - Teefer2 Miniport =========================================================================== =========================================================================== Active routes: Network Destination Netmask Gateway Interface Metrics 0.0.0.0 0.0.0.0 10.251.6.1 10.251.6.51 1 10.0.0.0 255.255.255.0 10.0.0.10 10.0.0.10 30 10.0.0.0 255.255.255.0 10.251.6.1 10.251.6.51 10 10.0.0.10 255.255.255.255 127.0.0.1 127.0.0.1 30 10.1.150.10 255.255.255.255 192.168.101.254 192.168.100.222 1 10.251.6.0 255.255.255.0 10.251.6.51 10.251.6.51 20 10.251.6.51 255.255.255.255 127.0.0.1 127.0.0.1 20 10.255.255.255 255.255.255.255 10.0.0.10 10.0.0.10 30 10.255.255.255 255.255.255.255 10.251.6.51 10.251.6.51 20 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 192.168.100.0 255.255.254.0 192.168.100.222 192.168.100.222 10 192.168.100.0 255.255.254.0 10.251.6.1 10.251.6.51 10 192.168.100.222 255.255.255.255 127.0.0.1 127.0.0.1 10 192.168.100.255 255.255.255.255 192.168.100.222 192.168.100.222 10 213.158.197.124 255.255.255.255 192.168.101.254 192.168.100.222 1 224.0.0.0 240.0.0.0 10.0.0.10 10.0.0.10 30 224.0.0.0 240.0.0.0 10.251.6.51 10.251.6.51 20 224.0.0.0 240.0.0.0 192.168.100.222 192.168.100.222 10 255.255.255.255 255.255.255.255 10.0.0.10 10.0.0.10 1 255.255.255.255 255.255.255.255 10.251.6.51 10.251.6.51 1 255.255.255.255 255.255.255.255 192.168.100.222 192.168.100.222 1 255.255.255.255 255.255.255.255 192.168.100.222 2 1 Default gateway: 10.251.6.1. ===========================================================================

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  • WCF Best Practice for "Overloaded" methods

    - by Nate Bross
    What is the best practice for emulating overloaded methods over WCF? Typically I might write an interface like this interface IInterface { MyType ReadMyType(int id); IEnumerable<MyType> ReadMyType(String name); IEnumerable<MyType> ReadMyType(String name, int maxResults); } What would this interface look like after you converted it to WCF?

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  • problem adding object to hashtable

    - by daemonkid
    I am trying to call a class method dynamically depending on a condition. This is how I am doing it I have three classes implement a single interface interface IReadFile { string DoStuff(); } The three classes A,B,C implement the interface above. I am trying to add them to a hashtable with the code below _HashT.Add("a", new classA()); _HashT.Add("b", new classB()); _HashT.Add("c", new classC()); This compiles fine, but gives a runtime error.{Object reference not set to an instance of an object.} I was planning to return the correct class to the interface type depending on a parameter that matches the key value. say if I send in a. ClassA is returned to the interface type and the method is called. IReadFile Obj = (IReadFile )_HashT["a"].GetType(); obj.DoStuff(); How do I correct the part above where the objects need to be added to the hashtable? Or do I need to use a different approach? All the classes are in the same assembly and namespace. Thanks for your time.

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  • Circular dependency with generics

    - by devoured elysium
    I have defined the following interface: public interface IStateSpace<State, Action> where State : IState where Action : IAction<State, Action> // <-- this is the line that bothers me { void SetValueAt(State state, Action action); Action GetValueAt(State state); } Basically, an IStateSpace interface should be something like a chess board, and in each position of the chess board you have a set of possible movements to do. Those movements here are called IActions. I have defined this interface this way so I can accommodate for different implementations: I can then define concrete classes that implement 2D matrix, 3D matrix, graphs, etc. public interface IAction<State, Action> { IStateSpace<State, Action> StateSpace { get; } } An IAction, would be to move up(this is, if in (2, 2) move to (2, 1)), move down, etc. Now, I'll want that each action has access to a StateSpace so it can do some checking logic. Is this implementation correct? Or is this a bad case of a circular dependence? If yes, how to accomplish "the same" in a different way? Thanks

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  • EF/LINQ: Where() against a property of a subtype

    - by ladenedge
    I have a set of POCOs, all of which implement the following simple interface: interface IIdObject { int Id { get; set; } } A subset of these POCOs implement this additional interface: interface IDeletableObject : IIdObject { bool IsDeleted { get; set; } } I have a repository hierarchy that looks something like this: IRepository<T <: BasicRepository<T <: ValidatingRepository<T (where T is IIdObject) I'm trying to add a FilteringRepository to the hierarchy such that all of the POCOs that implement IDeletableObject have a Where(p => p.IsDeleted == false) filter applied before any other queries take place. My goal is to avoid duplicating the hierarchy solely for IDeletableObjects. My first attempt looked like this: public override IQueryable<T> Query() { return base.Query().Where(t => ((IDeletableObject)t).IsDeleted == false); } This works well with LINQ to Objects, but when I switch to an EF backend I get: "LINQ to Entities only supports casting Entity Data Model primitive types." I went on to try some fancier parameterized solutions, but they ultimately failed because I couldn't make T covariant in the following case for some reason I don't quite understand: interface IQueryFilter<out T> // error { Expression<Func<T, bool>> GetFilter(); } I'd be happy to go into more detail on my more complicated solutions if it would help, but I think I'll stop here for now in hope that someone might have an idea for me to try. Thanks very much in advance!

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  • How to do something firstly when the asp.net server start

    - by Edwin Tai
    Hi all I need an interface that can be run firstly when the application start. We can write some code in Application_Start of global.ascx. Is there any other method to finish it after some configurations in web.config,i don't wanna write any code in global.ascx You know,we can implement the Interface 'IHttpModule' to diy each request. But the interface is not fix to application start. which one is i wanna? Thanks

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  • Can't get KnownType to work with WCF

    - by Kelly Cline
    I have an interface and a class defined in separate assemblies, like this: namespace DataInterfaces { public interface IPerson { string Name { get; set; } } } namespace DataObjects { [DataContract] [KnownType( typeof( IPerson ) ) ] public class Person : IPerson { [DataMember] public string Name { get; set; } } } This is my Service Interface: public interface ICalculator { [OperationContract] IPerson GetPerson ( ); } When I update my Service Reference for my Client, I get this in the Reference.cs: public object GetPerson() { return base.Channel.GetPerson(); I was hoping that KnownType would give me IPerson instead of "object" here. I have also tried [KnownType( typeof( Person ) ) ] with the same result. I have control of both client and server, so I have my DataObjects (where Person is defined) and DataInterfaces (where IPerson is defined) assemblies in both places. Is there something obvious I am missing? I thought KnownType was the answer to being able to use interfaces with WCF. ----- FURTHER INFORMATION ----- I removed the KnownType from the Person class and added [ServiceKnownType( typeof( Person ) ) ] to my service interface, as suggested by Richard. The client-side proxy still looks the same, public object GetPerson() { return base.Channel.GetPerson(); , but now it doesn't blow up. The client just has an "object", though, so it has to cast it to IPerson before it is useful. var person = client.GetPerson ( ); Console.WriteLine ( ( ( IPerson ) person ).Name );

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  • How does Sentry aggregate errors?

    - by Hugo Rodger-Brown
    I am using Sentry (in a django project), and I'd like to know how I can get the errors to aggregate properly. I am logging certain user actions as errors, so there is no underlying system exception, and am using the culprit attribute to set a friendly error name. The message is templated, and contains a common message ("User 'x' was unable to perform action because 'y'"), but is never exactly the same (different users, different conditions). Sentry clearly uses some set of attributes under the hood to determine whether to aggregate errors as the same exception, but despite having looked through the code, I can't work out how. Can anyone short-cut my having to dig further into the code and tell me what properties I need to set in order to manage aggregation as I would like? [UPDATE 1: event grouping] This line appears in sentry.models.Group: class Group(MessageBase): """ Aggregated message which summarizes a set of Events. """ ... class Meta: unique_together = (('project', 'logger', 'culprit', 'checksum'),) ... Which makes sense - project, logger and culprit I am setting at the moment - the problem is checksum. I will investigate further, however 'checksum' suggests that binary equivalence, which is never going to work - it must be possible to group instances of the same exception, with differenct attributes? [UPDATE 2: event checksums] The event checksum comes from the sentry.manager.get_checksum_from_event method: def get_checksum_from_event(event): for interface in event.interfaces.itervalues(): result = interface.get_hash() if result: hash = hashlib.md5() for r in result: hash.update(to_string(r)) return hash.hexdigest() return hashlib.md5(to_string(event.message)).hexdigest() Next stop - where do the event interfaces come from? [UPDATE 3: event interfaces] I have worked out that interfaces refer to the standard mechanism for describing data passed into sentry events, and that I am using the standard sentry.interfaces.Message and sentry.interfaces.User interfaces. Both of these will contain different data depending on the exception instance - and so a checksum will never match. Is there any way that I can exclude these from the checksum calculation? (Or at least the User interface value, as that has to be different - the Message interface value I could standardise.) [UPDATE 4: solution] Here are the two get_hash functions for the Message and User interfaces respectively: # sentry.interfaces.Message def get_hash(self): return [self.message] # sentry.interfaces.User def get_hash(self): return [] Looking at these two, only the Message.get_hash interface will return a value that is picked up by the get_checksum_for_event method, and so this is the one that will be returned (hashed etc.) The net effect of this is that the the checksum is evaluated on the message alone - which in theory means that I can standardise the message and keep the user definition unique. I've answered my own question here, but hopefully my investigation is of use to others having the same problem. (As an aside, I've also submitted a pull request against the Sentry documentation as part of this ;-)) (Note to anyone using / extending Sentry with custom interfaces - if you want to avoid your interface being use to group exceptions, return an empty list.)

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  • How can I manipulate a VB6 Collection in .NET?

    - by jhominal
    Hello all, I am currently in the process of designing an interface for .NET software that would be consumed by COM objects - specifically, VB6. While I have found a number of pages by Microsoft detailing how to make an COM-interoperable interface, I am currently tripping over the use of Collections in design time: I would like to be able to use a standard VB6 "Collection object" in the .NET program - for example, specify an argument as being a VB6 collection - and thus minimize the time necessary for clients to consume the interface. Thank you in advance.

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  • OpenMP implementations in VC++ 2008, 2010

    - by John
    Depending on implementation, OMP can be quite useful to parallelize fairly arbitrary bits of code - e.g a parallel section inside a method that calls two independent methods - or it can be bad. It depends on how threads are created/cached, I think. How does the VC++ 2008 implementation work? And is the 2010 implementation significantly different in terms of features and performance/flexibility?

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  • Django dictionary in templates: Grab key from another objects attribute

    - by Jordan Messina
    I have a dictionary called number_devices I'm passing to a template, the dictionary keys are the ids of a list of objects I'm also passing to the template (called implementations). I'm iterating over the list of objects and then trying to use the object.id to get a value out of the dict like so: {% for implementation in implementations %} {{ number_devices.implementation.id }} {% endfor %} Unfortunately number_devices.implementation is evaluated first, then the result.id is evaluated obviously returning and displaying nothing. I can't use parentheses like: {{ number_devices.(implementation.id) }} because I get a parse error. How do I get around this annoyance in Django templates? Thanks for any help!

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  • Is there a convention for organizing the include/exports in a large C++ project ?

    - by BlueTrin
    Hello, In a large C++ solution, is there a best/standard way to separate the include files necessary to build an intermediary DLL and the include files which will be used by the DLL clients ? We have grouped all the include files in a folder called Interface (for DLL interface), but there the customers have to either include the Interface folder as a default include folder or type the full name as: #include "ProjectName/Interface/myinterface.h" Wouldn't it be better to create a separate folder called exports where I would create a folder called ProjectName and put the include files there ? So that the customers would be typing: #include "ProjectName/myinterface.h" If I do the thing right above, then should I keep the files within the solution and produce a post build event (I use Visual Studio 2k5) to copy the files into the "export" folder (/ProjectName/) ? Or is it better to just include directly the files from this folder within my project (this is more direct and has less chances to cause maintenance issues ? I am more looking for advice than for a definite solution. Thank you for reading this ! Anthony

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  • desktop module for existing web application

    - by maxxxee
    My client has a running web application which has been online for more than a year. Recently the client has introduced smart cards for his employees. Because of the difficulty in integrating smart card with its api on a web interface(i will post another detailed question on this later) we are planning to have desktop interface for this. There are 10-20 terminals which will use the desktop interface. 3 approaches for doing this that I have considered : Direct connection and operations on DB-Not using this because of data integrity and consistency issues. Build web service end points and use it from desktop interface Build a dll with common functions and use from both web and desktop Questions: 1. What are your opinions based on 2 and 3 approach? 2. Any other approach that I should consider? Note: I am using .Net framework, web application in asp.net

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  • Castle windsor registration

    - by nivlam
    interface IUserService class LocalUserService : IUserService class RemoteUserService : IUserService interface IUserRepository class UserRepository : IUserRepository If I have the following interfaces and classes, where the IUserService classes have a dependency on IUserRepository. I can register these components by doing something like: container.AddComponent("LocalUserService", typeof(IUserService), typeof(LocalUserService)); container.AddComponent("RemoteUserService", typeof(IUserService), typeof(RemoteUserService)); container.AddComponent("UserRepository", typeof(IUserRepository), typeof(UserRepository)); ... and get the service I want by calling: IUserService userService = container.Resolve<IUserService>("RemoteUserService"); However, if I have the following interfaces and classes: interface IUserService class UserService : IUserService interface IUserRepository class WebUserRepository : IUserRepository class LocalUserRepository : IUserRepository class DBUserRepository : IUserRepository How do I register these components so that the IUserService component can "choose" which repository to inject at runtime? My idea is to allow the user to choose which repository to query from by providing 3 radio buttons (or whatever) and ask the container to resolve a new IUserService each time.

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  • iPhone - AES256 Encryption Using Built In Library

    - by Robert
    Hey all, I am using http://pastie.org/966473 as a reference as all I need to do is encrypt something using AES256 encrypting. I created a class and put the implementation in the pastie on top of the implementation for my class. @implementation //pastie code @end @implementation //my class code @end In my class code I create a NSMutableData and try to call the EncryptAES method and I get a warning saying it might not respond to that. What am I doing wrong here? do I need to implement the pastie code elsewhere? Thanks for any help.

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