The traditional way to do this is to use the Flags attribute on an enum:
[Flags]
public enum Names
{
None = 0,
Susan = 1,
Bob = 2,
Karen = 4
}
Then you'd check for a particular name as follows:
Names names = Names.Susan | Names.Bob;
// evaluates to true
bool susanIsIncluded = (names & Names.Susan) != Names.None;
// evaluates to false
bool karenIsIncluded = (names & Names.Karen) != Names.None;
Logical bitwise combinations can be tough to remember, so I make life easier on myself with a FlagsHelper class*:
// The casts to object in the below code are an unfortunate necessity due to
// C#'s restriction against a where T : Enum constraint. (There are ways around
// this, but they're outside the scope of this simple illustration.)
public static class FlagsHelper
{
public static bool IsSet<T>(T flags, T flag) where T : struct
{
int flagsValue = (int)(object)flags;
int flagValue = (int)(object)flag;
return (flagsValue & flagValue) != 0;
}
public static void Set<T>(ref T flags, T flag) where T : struct
{
int flagsValue = (int)(object)flags;
int flagValue = (int)(object)flag;
flags = (T)(object)(flagsValue | flagValue);
}
public static void Unset<T>(ref T flags, T flag) where T : struct
{
int flagsValue = (int)(object)flags;
int flagValue = (int)(object)flag;
flags = (T)(object)(flagsValue & (~flagValue));
}
}
This would allow me to rewrite the above code as:
Names names = Names.Susan | Names.Bob;
bool susanIsIncluded = FlagsHelper.IsSet(names, Names.Susan);
bool karenIsIncluded = FlagsHelper.IsSet(names, Names.Karen);
Note I could also add Karen to the set by doing this:
FlagsHelper.Set(ref names, Names.Karen);
And I could remove Susan in a similar way:
FlagsHelper.Unset(ref names, Names.Susan);
*As Porges pointed out, an equivalent of the IsSet method above already exists in .NET 4.0: Enum.HasFlag. The Set and Unset methods don't appear to have equivalents, though; so I'd still say this class has some merit.
Note: Using enums is just the conventional way of tackling this problem. You can totally translate all of the above code to use ints instead and it'll work just as well.
