c# - What does compile time 'const' mean?

Question

They say the difference between readonly and const is that const is compile-time (while readonly is run time). But what exactly does that mean, The fact that it's compile time? Everything gets compiled to byte code doesn't it?

Answer 1

It means that const variables get written to the location they are referenced from. So, say you have an 2 libraries, one with a const variable:

// Library A
const int TEST = 1;

// Library B
void m ()
{
   Console.WriteLine(A.TEST);
}

The variable is actually written, at compile time, into B. The difference is, if you recompile A but not B, B will have the "old" value. This won't happen with readonly variables.