Is there any performance increase by changing this .NET string to a const? Does the IL automatically do that?

Question

Given the following simple .NET code, is there any difference between these two, under the hood with respect to the string \"xml\"?

if (extension.Eq         


        

Answer 1

It is the same for the compiler. Basically both variables have no way of being changed at runtime.

This is an example:

public static void Main()
{
    Console.WriteLine("Hello World");

    const string hello = "Hello World";
    Console.WriteLine(hello);
}

Compiles to:

.method public hidebysig static void  Main() cil managed
  {
    // 
    .maxstack  8
    IL_0000:  nop
    IL_0001:  ldstr      "Hello World"
    IL_0006:  call       void [mscorlib]System.Console::WriteLine(string)
    IL_000b:  nop
    IL_000c:  ldstr      "Hello World"
    IL_0011:  call       void [mscorlib]System.Console::WriteLine(string)
    IL_0016:  nop
    IL_0017:  ret
  }

As you can see they are exactly the same. Compiler uses ldstr to push a string object for the literal string.

You can move const string outside method and it won't make a difference, because literals are treated as consts.