C# covariance on abstractly implemented interface
Using C#/.NET 4.0 I was hoping the following scenario would be possible:
interface IA<out TB> where TB : IB { }
interface IB { }
class A<TB> : IA<TB> where TB : IB { }
class B : IB { }
abstract class AbstractA<TB> : IA<TB> where TB : IB { }
class DerivedA<TB> : AbstractA<TB> where TB : IB { }
static void Main(string[] args) {
var myAB = new A<B>();
Debug.Assert(myAB is IA<B>); // fine
Debug.Assert(myAB is IA<IB>); // fine
var myDerivedAB = new DerivedA<B>();
Debug.Assert(myDerivedAB is IA<IB>); // fine
Debug.Assert(myDerivedAB is DerivedA<B>); // fine
Debug.Assert(myDerivedAB is DerivedA<IB>); // NOT fine
}
Sadly the last test fails, although the types clearly are compatible. Would there be another way to test this, other than testing for every known implementation of IB?
class FirstB : IB { }
class SecondB : IB { 开发者_JS百科}
Debug.Assert(myDerivedAB is DerivedA<FirstB> || myDerivedAB is DerivedA<SecondB>)
although the types clearly are compatible
No they aren't; C# covariance via out
applies only to interfaces and delegates (of reference-types, although that is fine here). It does not apply to classes such as Derived<T>
.
You can use GetGenericArguments method of Type object:
Type t = myDerivedAB.GetType();
if (t.IsGenericType)
{
Type[] typeArguments = t.GetGenericArguments();
Debug.Assert(typeArguments.Length > 0 && typeArguments[0] is IB);
}
By this you can get the Generic parameter of the myDerivedAB
object, and check its type, or something else you need.
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