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

I have another approach here that I just cooked up quickly using the fact that Delegate.CreateDelegate allows conversion between methods for Enum's and their underlying types. The following approach is much like my previous answer but I feel might be easier to read for people who don't know expression tree syntax. Basically we know that Enums only have 8 possible underlying types, and so we just create a static method for each call it could use. Since I'm going for brevity I use anonymous methods which happened to be named the same thing as the possible typecode values.This approach will work in .Net 3.5::

public static class EnumHelper
{
    delegate bool HasFlag(T left,T right);
    static readonly HasFlag Byte = (x,y)=> (x&y) ==y;
    static readonly HasFlag Sbyte = (x,y)=> (x&y) ==y;
    static readonly HasFlag Int16 = (x,y)=> (x&y) ==y;
    static readonly HasFlag UInt16 = (x,y)=> (x&y) ==y;
    static readonly HasFlag Int32 = (x,y)=> (x&y) ==y;
    static readonly HasFlag UInt32 = (x,y)=> (x&y) ==y;
    static readonly HasFlag Int64 = (x,y)=> (x&y) ==y;
    static readonly HasFlag UInt64 = (x,y)=> (x&y) ==y;

    public static bool HasFlags(this TEnum @enum,TEnum flag) where TEnum:struct,IConvertible,IComparable,IFormattable
    {
        return Enum.HasFlag(@enum,flag);
    }
    class Enum where TEnum:struct,IConvertible,IComparable,IFormattable
    {
        public static HasFlag HasFlag = CreateDelegate();
        static HasFlag CreateDelegate()
        {
            if (!typeof(TEnum).IsEnum) throw new ArgumentException(string.Format("{0} is not an enum", typeof(TEnum)), typeof(Enum<>).GetGenericArguments()[0].Name);
            var delegateName = Type.GetTypeCode(typeof(TEnum)).ToString();
            var @delegate = typeof(EnumHelper).GetField(delegateName,BindingFlags.Static | BindingFlags.NonPublic).GetValue(null) as Delegate;
            return Delegate.CreateDelegate(typeof(HasFlag), @delegate.Method) as HasFlag;
        }
    }
}