enumの拡張メソッド

class Program
{
  [STAThread]
  static void Main(string[] args)
  {
    TestFlag f = TestFlag.b | TestFlag.d; //bとdにフラグを立てる

    Console.WriteLine("{0}", f.HasFlag(TestFlag.a));
    Console.WriteLine("{0}", f.HasFlag(TestFlag.b));
    Console.WriteLine("{0}", f.HasFlag(TestFlag.c));
    Console.WriteLine("{0}", f.HasFlag(TestFlag.d));
    Console.WriteLine("{0}", f.HasFlag(TestFlag.e));
    Console.WriteLine("{0}", f.HasFlag(TestFlag.f));
    Console.Read();
  }
}

[Flags]
public enum TestFlag
{
  //値が被らないように設定
  a = 0x0001,
  b = 0x0002,
  c = 0x0004,
  d = 0x0008,
  e = 0x0010,
  f = 0x10000000
}

/// <summary>
/// Enum拡張メソッド
/// </summary>
public static class EnumExtension
{
  /// <summary>
  /// フラグを持っているか
  /// </summary>
  /// <param name="f"></param>
  /// <param name="e"></param>
  /// <returns></returns>
  public static bool HasFlag(this Enum f, Enum e)
  {
    /* fとeの論理積を取って、eと比較
     * f=00101
     * e=00100の時
     *   00100を返す
     */
    return (f & e) == e;
  }
}