List all classes that inherit from a specific class/interface

Question

I have an assembly, and I want to list all classes that inherit from a specific class/interface.

How would I do this?

Answer 1

Something like:

public static IEnumerable<Type> GetSubtypes(Assembly assembly, Type parent)
{
    return assembly.GetTypes()
                   .Where(type => parent.IsAssignableFrom(type));
}

That's fine for the simple case, but it becomes more "interesting" (read: tricky) when you want to find "all types implementing IEnumerable<T> for any T" etc.

(As Adam says, you could easily make this an extension method. It depends on whether you think you'll reuse it or not - it's a pain that extension methods have to be in a non-nested static class...)

Answer 2

public static IEnumerable<Type> GetTypesThatInheritFrom<T>(this Assembly asm)
{
    var types = from t in asm.GetTypes()
                where typeof(T).IsAssignableFrom(t)
                select t;
    return types;
}