C# Dynamic Keyword — Run-time penalty?

user_456909 0
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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 does for all instances.

  2. The compiler does not perform compile-time type checking, but run-time checking takes place, unlike with any other non-dynamic instances.

  3. Same as 2, and this comes with performance penalty (trivial? potentially significant?).

dynamic performance c#
6 Answers

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.

user_62727370
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