Generic extension method to see if an enum contains a flag

Question

Considering this:

[Flags]
public enum MyEnum {
    One = 1,
    Two = 2,
    Four = 4,
    Eight = 8
}

public static class FlagsHelper
{
    public static bool          


        

Answer 1

Unfortunately no there is not a good way to make an extension method like this. In order for this to work you'd need to have a generic method which operated on enum values. Unfortunately there is no way to constrain generic arguments to be an enum

// Ilegal
public static bool Contains(this T value, T flag) where T : enum {
  ...
}

The best I've come up with is the following

public static bool HasFlag(this System.Enum e, T flag) 
{
    var intValue = (int)(object)e;
    var intFlag = (int)(object)flag;
    return (intValue & intFlag) != 0;
}

However it's limited in several ways

• Not type safe because there is no requirement the value and the flag have the same type
• Assumes that all enum values are int based.
• Causes boxing to occur for a simple bit check
• Will throw if e is null