Why dynamic call return dynamic result?

Question

public string Foo(object obj) {
    return null;
}

public string Foo(string str) {
    return null;
}

var x = Foo((dynamic) "abc");

Why is x dynamic, compiler not smart enough or I miss something important?

Answer 1

I'm just guessing here, but...

When you add a cast to dynamic, the entire expression becomes a dynamic expression. The result of a dynamic expression is always going to be dynamic because everything is resolved at run-time.

Check out the MSDN page on using dynamic for more info:

Using Type dynamic (C# Programming Guide)

And scroll to the following text:

The result of most dynamic operations is itself dynamic.