How can you know if a type implements a particular generic interface type?

Problem

Take the following type definitions into consideration:

public interface IFoo<T> : IBar<T> {}
public class Foo<T> : IFoo<T> {}

When just the mangled type is provided, how do I find out if the type Foo implements the generic interface IBarT>?

Asked by sduplooy

Solution #1

It may also be done with the following LINQ query, which uses TcKs’ answer:

bool isBar = foo.GetType().GetInterfaces().Any(x =>
  x.IsGenericType &&
  x.GetGenericTypeDefinition() == typeof(IBar<>));

Answered by sduplooy

Solution #2

You must walk up the inheritance tree and identify all of the interfaces for each class in the tree, then compare typeof(IBar>) with the Type result. If the interface is generic, use GetGenericTypeDefinition. It’s all a little painful, to be sure.

For further information and code, see this and these answers.

Answered by Jon Skeet

Solution #3

public interface IFoo<T> : IBar<T> {}
public class Foo : IFoo<Foo> {}

var implementedInterfaces = typeof( Foo ).GetInterfaces();
foreach( var interfaceType in implementedInterfaces ) {
    if ( false == interfaceType.IsGeneric ) { continue; }
    var genericType = interfaceType.GetGenericTypeDefinition();
    if ( genericType == typeof( IFoo<> ) ) {
        // do something !
        break;
    }
}

Answered by TcKs

Solution #4

As a method extension, this is referred to as a “helper method.”

public static bool Implements<I>(this Type type, I @interface) where I : class
{
    if(((@interface as Type)==null) || !(@interface as Type).IsInterface)
        throw new ArgumentException("Only interfaces can be 'implemented'.");

    return (@interface as Type).IsAssignableFrom(type);
}

Example usage:

var testObject = new Dictionary<int, object>();
result = testObject.GetType().Implements(typeof(IDictionary<int, object>)); // true!

Answered by GenericProgrammer

Solution #5

I’m using the @GenericProgrammers extension method in a little simplified form:

public static bool Implements<TInterface>(this Type type) where TInterface : class {
    var interfaceType = typeof(TInterface);

    if (!interfaceType.IsInterface)
        throw new InvalidOperationException("Only interfaces can be implemented.");

    return (interfaceType.IsAssignableFrom(type));
}

Usage:

    if (!featureType.Implements<IFeature>())
        throw new InvalidCastException();

Answered by Ben Foster

Post is based on https://stackoverflow.com/questions/503263/how-to-determine-if-a-type-implements-a-specific-generic-interface-type