http://ayende.comAyende @ RahienCopyright (C) Ayende Rahien 2004 - 2021 (c) 202660Should be "public class Foo<TFromClass> : IFoo<TFromClass> { }". http://ayende.com/2892/more-generics-gotchas-argh#comment5http://ayende.com/2892/more-generics-gotchas-argh#comment5Tue, 23 Oct 2007 22:36:28 GMTIncidentally, another way to make it pass is to specify any generic param: Assert.AreEqual(typeof(IFoo<Bar>), typeof(Foo<Bar>).GetInterfaces()[0]); or : Assert.IsTrue(typeof(IFoo<Bar>).IsAssignableFrom(typeof(Foo<Bar>))); http://ayende.com/2892/more-generics-gotchas-argh#comment4http://ayende.com/2892/more-generics-gotchas-argh#comment4Tue, 23 Oct 2007 20:25:25 GMTAvish, Yes, that was what I ended up doing. The problem is that it took me a long time to get to the point of "Oh, so _that_ is it" http://ayende.com/2892/more-generics-gotchas-argh#comment3http://ayende.com/2892/more-generics-gotchas-argh#comment3Tue, 23 Oct 2007 19:22:52 GMTI was a little puzzled by it too on the first time, but when I ventured deeper into generics I realized this really is very logical. In fact, it wouldn't make sense any other way. See, when you say: public class Foo<T> : IFoo<T> The first <T> means "I'm declaring a generic parameter, let's call it T". But the second one means "Now I'm USING said generic parameter, in effect saying that any type constructed from Foo<T> will implement IFoo<T> *for the same T*." The fact that you used the same name (T) for the generic parameter declaration on IFoo is irrelevant; inside the scope of the generic class, T refers to the already-declared generic parameter. If IFoo<T> had IFoo<> in its interface map, nothing would work. That's more apparent when you consider stuff like "public class Thingy<T> : IFoo<IEnumerable<T>>". Here it's very obvious that you want the implemented interface to use the unbound generic parameter T, so that when you construct a concrete type out of that generic type, using System.Int32 for T, it'd implement IFoo<IEnumerable<int>>. . If that's any comfort, you can still do: Assert.AreEqual( typeof(IFoo<>), typeof(Foo<>).GetInterfaces()[0].GetGenericDefinition()); http://ayende.com/2892/more-generics-gotchas-argh#comment2http://ayende.com/2892/more-generics-gotchas-argh#comment2Tue, 23 Oct 2007 19:16:29 GMTI've found this post to be quite helpful: http://blogs.msdn.com/dinesh.kulkarni/archive/2005/09/09/463001.aspx http://ayende.com/2892/more-generics-gotchas-argh#comment1http://ayende.com/2892/more-generics-gotchas-argh#comment1Tue, 23 Oct 2007 17:22:34 GMT