How to check if any flags of a flag combination are set?

Question

Let's say I have this enum:

[Flags]
enum Letters
{
     A = 1,
     B = 2,
     C = 4,
     AB = A | B,
     All = A | B | C,
}

To check if for example AB is set I can do this:

if((letter & Letters.AB) == Letters.AB)

Is there a simpler way to check if any of the flags of a combined flag constant are set than the following?

if((letter & Letters.A) == Letters.A || (letter & Letters.B) == Letters.B)

Could you for example swap the & with something?

Not too stable when it comes to binary stuff like this...

Answer 1

In .NET 4 you can use the Enum.HasFlag method :

using System;

[Flags] public enum Pet {
   None = 0,
   Dog = 1,
   Cat = 2,
   Bird = 4,
   Rabbit = 8,
   Other = 16
}

public class Example
{
   public static void Main()
   {
      // Define three families: one without pets, one with dog + cat and one with a dog only
      Pet[] petsInFamilies = { Pet.None, Pet.Dog | Pet.Cat, Pet.Dog };
      int familiesWithoutPets = 0;
      int familiesWithDog = 0;

      foreach (Pet petsInFamily in petsInFamilies)
      {
         // Count families that have no pets. 
         if (petsInFamily.Equals(Pet.None))
            familiesWithoutPets++;
         // Of families with pets, count families that have a dog. 
         else if (petsInFamily.HasFlag(Pet.Dog))
            familiesWithDog++;
      }
      Console.WriteLine("{0} of {1} families in the sample have no pets.", 
                        familiesWithoutPets, petsInFamilies.Length);   
      Console.WriteLine("{0} of {1} families in the sample have a dog.", 
                        familiesWithDog, petsInFamilies.Length);   
   }
}

The example displays the following output:

//       1 of 3 families in the sample have no pets. 
//       2 of 3 families in the sample have a dog.