Extension method restricted to objects containing specific properties

Question

Is there any way to create an extension method whose parameter's only constraint is having specifically-named properties. e.g.:

public static bool IsMixed<T>(this T obj) where T:?
{
    return obj.IsThis && obj.IsThat;
} 

I tried to declare the obj as dynamic but it's not allowed.

Answer 1

This feature is often called "duck typing". (Because when you call foo.Quack() all you care about is that it quacks like a duck.) Non-dynamic duck typing is not a feature of C#, sorry!

If you really have no type information about the argument, you can use dynamic in C# 4:

public static bool IsAllThat(this object x)
{
    dynamic d = x;
    return d.IsThis || d.IsThat;
}

But it would be better to come up with some interface or some such thing that describes the types at compile time.