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

I made a simple test: 100000000 assignments to a variable as a dynamic vs. the same number of direct double assignments, something like

int numberOfIterations = 100000000;

Stopwatch sw = new Stopwatch();
sw.Start();

for (int i = 0; i < numberOfIterations; i++)
{
    var x = (dynamic)2.87; 
}

sw.Stop();
sw.Restart();

for (int i = 0; i < numberOfIterations; i++)
{
    double y = 2.87; 
}
sw.Stop();

In the first loop (with dynamic) it took some 500ms; in the second one about 200ms. Certainly, the performance loss depends of what you do in your loops, these representing a simplest action possible.