How to generically combine all bits (I mean OR all values) of a [FLAGS] enum, having only valid values (bits) declared in the resulting enum?

Question

How to generically combine all bits (I mean OR all values) of a [FLAGS] enum, having only valid values (bits) declared in the enum?

Ex: [Flags] enum SuitsFlags { Spades = 1, Clubs = 2, Diamonds = 4, Hearts = 8 } => Expected solution would: return Spades | Clubs | Diamonds | Hearts; but using a generic function.

I try to ask the question previously but I asked the wrong question: Enum fun... Why these 2 errors.... My question was closed but peoples gave me some great clues on how to do it. I finally did it with pretty much works (trial and errors). So I wanted to leave a trace of my solution to help others, and potentially have better solution from other users too.

It is not the first time I need that. Although anybody can do it quickly by OR (val1 | val2 | ...) each values manually, that could lead to runtime error when a new enum value is added and the programmer forget to verify each and every places where the enum is used.

Answer 1

This is my second answer which I prefer because of its advantages:

• It has no unsafe code.
• It does not require compilation.
• It's probably faster on first call than any code requiring compilation
• It should also be the fastest on subsequent calls, due to the caching

Usage sample:

private ItemCategory _categoryFilter = EnumFlagsAll<ItemCategory>.Value;

Code:

public static class EnumFlagsAll<T> where T : struct, Enum
    {
        // **************************************************************
        static EnumFlagsAll()
        {
            T res = default;
            foreach (T val in Enum.GetValues<T>())
            {
                res = (T)GenericAddBits(res, val);
            }
            Value = res;
        }

        public static T Value { get; }

        // **************************************************************
        /// <summary>
        /// Generic method to add bit(s) from the first value. Will perform an OR.
        /// </summary>
        /// <param name="val"></param>
        /// <param name="bitsToAdd"></param>
        /// <returns></returns>
        public static Enum GenericAddBits(Enum val, Enum bitsToAdd)
        {
            // consider adding argument validation here

            return (Enum)Enum.ToObject(val.GetType(), Convert.ToUInt64(val) | Convert.ToUInt64(bitsToAdd));
        }

        // **************************************************************
    }