How do I find out whether an object's type is a subclass of IEnumerable for any value type T?

Question

I need to validate an object to see whether it is null, a value type, or IEnumerable where T is a value type. So far I have:

Answer 1

(edit - added value type bits)

You need to check all the interfaces it implements (note it could in theory implement IEnumerable<T> for multiple T):

foreach (Type interfaceType in obj.GetType().GetInterfaces())
{
    if (interfaceType.IsGenericType
        && interfaceType.GetGenericTypeDefinition() == typeof(IEnumerable<>))
    {
        Type itemType = interfaceType.GetGenericArguments()[0];
        if(!itemType.IsValueType) continue;
        Console.WriteLine("IEnumerable-of-" + itemType.FullName);
    }
}

Answer 2

My generic contribution that checks if a given type (or its base classes) implements an interface of type T:

public static bool ImplementsInterface(this Type type, Type interfaceType)
{
    while (type != null && type != typeof(object))
    {
        if (type.GetInterfaces().Any(@interface => 
            @interface.IsGenericType
            && @interface.GetGenericTypeDefinition() == interfaceType))
        {
            return true;
        }

        type = type.BaseType;
    }

    return false;
}

Answer 3

Can you do somethin with GetGenericArguments ?