Suppose I have an empty interface class IBaseInterface which is used only to "label" implementing classes as being interfaces themselves.
Is there any way to do something like this?
For example:
public class MyClass : T where T : IBaseInterface
{
}
No, you can't do that, since the compiler has to know which interface the class implements when you declare the class. You can have generic parameters to the interface, but the actual interface has to be specified.
Not like that, there isn't. I would strongly recommend using a composition pattern to try and achieve whatever you're trying. As an alternative, you might find DynamicProxy (or some other proxy solution) is what you're going for.
The type you're declaring isn't even generic. Something like this:
class MyClass<T> : T where T : IBaseInterface
could work under some circumstances (for example, if C++ templates were used instead of .Net generics), but it's simply not valid C# code.
I'm not sure what are the “labels” used for, but an interface with a property
ClassType ClassType { get; }
where
ClassType is an enum could work.
Related
I want to implement a non-generic version of my generic class. Like this.
public class ServerSentEvent : ServerSentEvent<NoAdditionalClientInformation>
public class ServerSentEvent<ClientInfo> : IServerSentEvent
To solve this I had to make a dummy/empty class - NoAdditionalClientInformation.
Is there another way to do this without the empty class?
Usually you’d just do it the other way around:
public class ServerSentEvent : IServerSentEvent
{}
public class ServerSentEvent<ClientInfo> : ServerSentEvent
{}
That way the generic version is a more specified subtype of the non-generic one allowing you to put more information in it but to use the generic type whereever a non-generic type is expected.
If you do it like you suggested, you would need to have to specify some default type; if you can’t think of a default one, it is probably the wrong order, but in general it might depend on the case.
Can I add a dynamic method to an interface in c#?
So the interface method doesn't exist but exists on the underlying class and I want to call it via an interface.
thanks
That kind of defeats the point of an interface. If you want it on some of the classes and not others then you can implement it that way, but you will have to cast it to the known class type first.
You could probably use some reflection to check in the under-laying class type has the method you want to call if you want to be really fussy about it (and avoid knowing the type to cast)
Try making a new interface that implements the original interface as a sort of "middle man" between your class and the underlying interface
public interface IFoo
{
string PropA { get; set; }
}
public interface IFooExtended
{
void MyMethod();
}
public class ConcreteFoo : IFooExtended
{
// implementation...
}
It's not "dynamic" but this may help.
No - you could add an extension method to the interface to achieve a similar objective.
I think the right practice to follow that is as close as possible to what you're trying to achieve is create a new interface that inherits the old one.
Something like:
interface IMyInterface : IExistingInterface
{
void MyCustomMethod();
}
And you will address your new interface in your code. The classes implementing it will have your new method as well as the methods of the inherited interface.
You can't alter an existing interface, that would defeat the purpose of an interface itself.
If you're asking if you want to use a dynamic interface (e.g., strong-typed duck typing like in Visual Basic), then no, C# doesn't natively support this. But you can check out the Code Project article, Dynamic interfaces in any .NET language.
I have a Generic Interface
public interface TheInterface<T> where T : IObject
I also have an object class that this interface works with
public class SomeObject : IObject
I then have a class that implements the interface
public class ClassThatWorksWithSomeObject : TheInterface<SomeObject>
This all works well enough. Later on I add a class that works with TheInterface class independent of what version of IObject he uses.
public class IDoStuffToInterface
{
public IDoStuffToInterface(TheInterface<IObject> interface)
{
//bla bla
}
}
Problem is I can't pass ClassThatWorksWithSomeObject in there, even if It inherits from the intreface and it's generic object inherits from IObject.
I guess there are some cases that it could be hurtful if it did, but I can't think of any.
Is there a way to do this better?
I don't know the detail impelmentation, you can try:
public interface TheInterface<out T> where T : IObject
if you are using C#4.0
I think what you're doing should work, but you may need to use the covariance and contravariance keywords.
You need to make you definition of TheInterface covariant so that it accepts the wider types of IObject:
public interface TheInterface<out T> where T : IObject
You should be able to do this in C#4.0 by marking the interface type as contravariant, but I think you can also get around this by making the IDoStuffInterface generic as well.
public class IDoStuffToInterface<T> where T : IObject
{
public IDoStuffToInterface(TheInterface<T> interface)
{
//bla bla
}
}
Since SomeObject qualifies for T and ClassThatWorksWithSomeObject implements TheInterface<SomeObject>, it should be acceptable as a parameter.
The other way I saw mentioned by tvanfosson was to make your IDoStuffToInterface class generic. That would work nicely as well, if (as it appears in the example) the TheInterface is being passed into the constructor and (presumably) stored in the class.
However, if it were just a function (or even a constructor) that uses the TheInterface and it isn't being stored in the class, it would probably be better to make the function itself generic and leave the class alone. For example:
public class IDoStuffToInterface
{
public void DoSomething<T>(TheInterface<T> theInterface) where T : IObject
{
//bla bla
}
}
This would allow you to do the following:
ClassThatWorksWithSomeObject myObject = new ClassThatWorksWithSomeObject();
IDoStuffToInterface actor = new IDoStuffToInterface();
actor.DoSomething(myObject);
That compiles without any problem because the compiler is able to tell by inference that you are actually calling
actor.DoSomething<SomeObject>(myObject);
Now, I think that using covariance is still probably the best option if you are in control of the interface definition. But I wanted to add this as another option for when you don't have that degree of control in your interface.
I have a generic interface:
public interface IUnauthorizedRequestRespondable<out T> where T:class
{
T GetResponseForUnauthorizedRequest();
}
(I'm not sure why Resharper recommended T is "out", but that's not the question).
In my scenario, the object returned by GetResponseForUnauthorizedRequest is always of the type that implements the interface.
So all the interface's implementations look like:
public class SignInReturnedObject : IUnauthorizedRequestRespondable<SignInReturnedObject>
(class name and the type in brackets are always the same).
Which seems a bit awkward - isn't there a neater way to tell the compiler that the interface's method returns the type it's a part of?
Thanks.
As far as I know, there is no way to do that currently in C#.
A theoretical side-note: The feature that would allow you to do this is called self types but that's not available in C#. The idea of the feature is that you have a special type that refers to the actual type of this, so if you had a special type named self, you could probably write something like:
public interface IUnauthorizedRequestRespondable {
self GetResponseForUnauthorizedRequest();
}
...and the actual type used in place of self when you have a class SignInReturnedObject implementing the interface would be SignInReturnedObject, but unfortunatelly, that's not
available in C# :-)
If the only way you want to use that template is in that manner, I would use:
public interface IUnauthorizedRequestRespondable<T> where T:IUnauthorizedRequestRespondable<T>
{
T GetResponseForUnauthorizedRequest();
}
This has the advantage of guaranteeing it isn't used in any other way.
The class declaration won't change, but I don't see anything as awkward in this myself. Considering that you are defining a relationship between the class and itself, any more concise form might be inadvisable.
Actually, that about sums it up. That is how the syntax works.
You can see it used in .NET itself with the IEquatable inteface--you are almost always comparing an object to itself, yet you always have to provide your own class name as a template parameter.
This is simply to provide flexibility such that you can compare to anything, not necessarily yourself.
You can create a nongeneric version and just use that but I think it is more trouble than it is worth
public interface ICastUnauthorizedRequestRespondable : IUnauthorizedRequestRespondable<SignInReturnedObject>
{
}
Since T can be any class (does not have to be the class you are implementing) you need to name your class.
public class SignInReturnedObject : IUnauthorizedRequestRespondable<ANYCLASS>
I want to achieve something like this in C# 3.5:
public void Register<T>() : where T : interface {}
I can do it with class or struct, but how to do it with an interface?
If you are asking about adding a constraint to a specific interface, that's straightforward:
public void Register<T>( T data ) where T : ISomeInterface
If you are asking whether a keyword exists like class or struct to constrain the range of possible types for T, that is not available.
While you can write:
public void Register<T>( T data ) where T : class // (or struct)
you cannot write:
public void Register<T>( T data ) where T : interface
C# and the CLR don't support overall interface constraints, although you can constrain it to a particular interface (see other answers). The closest you can get is 'class' and check the type using reflection at runtime I'm afraid. Why would you want an interface constraint in the first place?
You can't demand that T is an interface, so you'd have to use reflection at runtime to assert this.
If possible, I went with a solution like this. It only works if you want several specific interfaces (e.g. those you have source access to) to be passed as a generic parameter, not any.
I let my interfaces, which came into question, inherit an empty interface IInterface.
I constrained the generic T parameter to be of IInterface
In source, it looks like this:
Any interface you want to be passed as the generic parameter:
public interface IWhatever : IInterface
{
// IWhatever specific declarations
}
IInterface:
public interface IInterface
{
// Nothing in here, keep moving
}
The class on which you want to put the type constraint:
public class WorldPieceGenerator<T> where T : IInterface
{
// Actual world piece generating code
}