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10.4.2.2 Versioning of constants and static readonly fields

Visual Studio .NET 2003

Constants and readonly fields have different binary versioning semantics. When an expression references a constant, the value of the constant is obtained at compile-time, but when an expression references a readonly field, the value of the field is not obtained until run-time. Consider an application that consists of two separate programs:

using System;
namespace Program1
{
   public class Utils
   {
      public static readonly int X = 1;
   }
}
namespace Program2
{
   class Test
   {
      static void Main() {
         Console.WriteLine(Program1.Utils.X);
      }
   }
}

The Program1 and Program2 namespaces denote two programs that are compiled separately. Because Program1.Utils.X is declared as a static readonly field, the value output by the Console.WriteLine statement is not known at compile-time, but rather is obtained at run-time. Thus, if the value of X is changed and Program1 is recompiled, the Console.WriteLine statement will output the new value even if Program2 is not recompiled. However, had X been a constant, the value of X would have been obtained at the time Program2 was compiled, and would remain unaffected by changes in Program1 until Program2 is recompiled.

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