c# - Performance of TypeCasting

Question

is there any measurably performance difference between

((TypeA) obj).method1();
((TypeA) obj).method2();
((TypeA) obj).method3();

and

var A = (TypeA) obj;
A.method1();
A.method2();
A.method3();

when used alot of times?

I often see something like

if (((TextBox)sender).Text.Contains('.') || ((TextBox)sender).Text.Contains(','))

and wonder if this is a waste of performance.

Answer 1

It may be measurable if it's being done billions of times with very little other work. I don't know whether the CLR will effectively cache the fact that the cast worked, so it doesn't need to do it again - if it doesn't do so now, it might do so in a later release. It might do so in the 64 bit JIT but not the 32 bit version, or vice versa - you get the idea. I doubt that it would make a significant difference in normal code though.

Personally I like the readability of the second form more though, and that's more important by far.