Ch07-5-Fields.cs

#pragma warning disable 169

using System;

public sealed class SomeType {
	// This is a static read-only field; its value is calculated and
	// stored in memory when this class is initialized at run time.
	public static readonly Random s_random = new Random();

	// This is a static read/write field.
	private static Int32 s_numberOfWrites = 0;

	// This is an instance read-only field.
	public readonly String Pathname = "Untitled";

	// This is an instance read/write field.
	private System.IO.FileStream m_fs;

	public SomeType(String pathname) {
		// This line changes a read-only field. 
		// This is OK because the code is in a constructor.
		this.Pathname = pathname;
	}

	public String DoSomething() {
		// This line reads and writes to the static read/write field.
		s_numberOfWrites = s_numberOfWrites + 1;

		// This line reads the read-only instance field.
		return Pathname;
	}
}

internal static class ReadOnlyReferences {
   public sealed class AType {
      // InvalidChars must always refer to the same array object
      public static readonly Char[] InvalidChars = new Char[] { 'A', 'B', 'C' };
   }

   public sealed class AnotherType {
      public static void M() {
         // The lines below are legal, compile, and successfully 
         // change the characters in the InvalidChars array
         AType.InvalidChars[0] = 'X';
         AType.InvalidChars[1] = 'Y';
         AType.InvalidChars[2] = 'Z';

         // The line below is illegal and will not compile because 
         // what InvalidChars refers to cannot be changed
         //AType.InvalidChars = new Char[] { 'X', 'Y', 'Z' };
      }
   }
}