How can I get a collection of set bits from an instance of a flags enum?

Question

The Enum class has the following useful function:

public static Array GetValues(Type enumType);

How could I write something similar to give me a collection of all an enum instance's set bits? With a signature like:

public static IEnumerable<T> getFlagValues<T>(this Enum enum, T enumInstance) where T : struct;

I am having trouble getting the casting to work, as I'm not allowed to constrain by Enum so I need to use struct.

Answer 1

I think that you mean like this:

public static IEnumerable<T> getFlagValues<T>(this T enumValue) where T : struct {
  foreach (object o in Enum.GetValues(typeof(T))) {
    if (((int)o & (int)(object)enumValue) != 0) yield return (T)o;
  }
}

You only need one parameter, as you would call it on the enum value. Example:

[Flags]
public enum X { a = 1, b = 2, c = 4 }

X x = X.a | X.c;

foreach (var n in x.getFlagValues()) {
  Console.WriteLine(n);
}

Output:

a
c