Enum types should fit bitwise operator generic type constraint

[anranruye]

Intuitively an enum type can be used as the type T in the following code, but exactly not.

        public static T Or<T>(T a, T b) where T : IBitwiseOperators<T, T, T>
        {
            return a | b;
        }

Of course we know that we can not explicitly implement any interface on an enum type, but obviously enum types implement the IBitwiseOperators interface naturally.

More code is here:

    internal class Program
    {
        public static void Main(string[] args)
        {
            MyEnum a = MyEnum.A;
            MyEnum b = MyEnum.B;
            var c = Or(a, b); // doesn't work
            // the following statements are ok
            var d = a & b;
            d = a | b;
            d = a ^ b;
            d = ~a;
        }

        public static T Or<T>(T a, T b) where T : IBitwiseOperators<T, T, T>
        {
            return a | b;
        }

        enum MyEnum : int
        {
            A = 1,
            B = 2,
            C = 4,
        }
    }

[bachratyg]

Related
dotnet/runtime#73579 (comment)
dotnet/roslyn#67905

[TahirAhmadov]

I think this is a runtime request, not a C# request.

[bachratyg]

See link above

This would likely require a combination of runtime and language changes to support, but it needs language buy off before anything could be done [issue closed]

[CyrusNajmabadi]

@tannergooding if you feel this is worthwhile.

[tannergooding]

This would require some level of runtime support such as to allow enums to declare interfaces, such as to allow System.Enum to implement the operators and then specially handle the codegen, or such as to allow extension interface to be defined and implemented.

It likely requires more in depth discussion with the runtime team on what is the best approach and that should probably start with an issue being opened on dotnet/runtime (if one doesn't exist already).

[bachratyg]

The runtime issue linked above (closed and locked) can be repurposed, it's about the same thing. Or should there be a new one?