C# Dynamic Keyword — Run-time penalty?

Question

Does defining an instance as dynamic in C# mean:

1. The compiler does not perform compile-time type checking, but run-time checking takes place like it always

Answer 1

Well, the variable is statically typed to be of the type dynamic but beyond that the compiler doesn't do any checking as far as I know.

Type binding is done at runtime and yes, there's a penalty, but if dynamic is the only option then so what. If you can solve the problem using static typing do so. That being said, the DLR does call site caching which means some of the overhead is reduced as the plumbing can be reused in some cases.