Is there any reason to use enum params over bit flags in c#?

Question

Lets say, for example, I have two implementations, one with bit flags and one with simple enum:

1) bit flags

[Flags]
public enum LettersBitFlags
{
    A = 1,
    B = 2,
    C = 4,
    D = 8
}

public static bool IsLetterBBitFlags(LettersBitFlags letters)
{
    return (letters & LettersBitFlags.B) != 0;
}

2) simple enum

public enum Letters
{
    A,
    B,
    C,
    D
}

public static bool IsLetterBParams(params Letters[] letters)
{
    return letters.Any(x => x == Letters.B);
}

They obviously can be used like this:

Console.WriteLine(IsLetterBBitFlags(LettersBitFlags.A | LettersBitFlags.D)); //false
Console.WriteLine(IsLetterBBitFlags(LettersBitFlags.B | LettersBitFlags.C)); //true

Console.WriteLine(IsLetterBParams(Letters.A, Letters.D)); //false
Console.WriteLine(IsLetterBParams(Letters.B, Letters.C)); //true

Is there any practical reason to choose one over the other? As I see, they give the same result, but maybe some performance or anything else should make me use one and did not use the other?

score 1 · Accepted Answer · answered May 31 '20 at 14:29

They have different meanings. Flags are characterised by the fact that it's meaningful to OR them together; enums are simply discrete lumps of data, and the fact that they are numerical under the covers is nothing more than an implementation detail.

If you use flags where it's not meaningful to OR two of them together, you will badly mislead anyone who comes to use your data type. Conversely, if you use an enum where you meant a flag, then you'll have to manually capture and name exponentially many enum cases.

score 1 · Answer 2 · answered May 31 '20 at 14:30

Advantages of bit flags:

1) The flags attribute gives you nicer ToString() behaviour than an array of an enum.

2) You can store multiple values in one variable (hence why you don't need an array). This could be important in a memory bound operation.

3) The method Enum.HasFlag exists so you don't actually have to implement your static class.

Disadvantages:

1) You cannot store multiple instances of the same value in the flag - on/off. Your array could have multiple instances of the same value.

2) Any = 0 value will have to be checked separately if you want one.

3) In my option it's not always as clear what you're doing when using bit flags - there's an extra element of knowledge that you need.

If you use flags you may want a `None = 0` option - that won't be a flag though so you have to check it separately from the rest of your logic. — SBFrancies, May 31 '20 at 20:06

score 0 · Answer 3 · answered May 31 '20 at 14:25

0

The 1st option is good when you represent data in some byte/ int bits, and the data may contain 1 or more of the enum values and then you ca check if data has flag or not.

answered May 31 '20 at 14:25

Michael Gabbay

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Is there any reason to use enum params over bit flags in c#?

3 Answers3