Comparing enum flags in C#

Question

I need to detect if a flag is set within an enum value, which type is marked with the Flag attribute.

Usually it is made like that:

(value & flag) ==         


        

Answer 1

This should do the job for enum types with any underlying types:

public static bool IsSet(this T value, T flags) where T : struct
{
    return (Convert.ToInt64(value) & Convert.ToInt64(flags)) ==
        Convert.ToInt64(flags);
}

Convert.ToInt64 is used because a 64-bit integer is the "widest" integral type possible, to which all enum values can be cast (even ulong). Note that char is not a valid underlying type. It seems that it is not valid in C#, but it is in general valid in CIL/for the CLR.

Also, you can't enforce a generic type constraint for enums (i.e. where T : struct); the best you can do is use where T : struct to enforce T to be a value type, and then optionally perform a dynamic check to ensure that T is an enum type.

For completeness, here is my very brief test harness:

static class Program
{
    static void Main(string[] args)
    {
        Debug.Assert(Foo.abc.IsSet(Foo.abc));
        Debug.Assert(Bar.def.IsSet(Bar.def));
        Debug.Assert(Baz.ghi.IsSet(Baz.ghi));
    }

    enum Foo : int
    {
        abc = 1,
        def = 10,
        ghi = 100
    }

    enum Bar : sbyte
    {
        abc = 1,
        def = 10,
        ghi = 100
    }

    enum Baz : ulong
    {
        abc = 1,
        def = 10,
        ghi = 100
    }
}