What Does the [Flags] Attribute Really Do?

Question

What does applying [Flags] really do?

I know it modifies the behavior of Enum.ToString, but does it do anything else? (e.g. Different compiler or runtime behavior, e

Answer 1

In practice, one of the uses I use is indicating multiple statuses. This is a simplification of some code that evaluates test results. The test can be Ok, or it could have several reasons for not being Ok. The advantage this gives, is I have one method that evaluates the tests "Ok-ness", and that method is able to indicate all the possible failure conditions with one return. May not be the best design, but it works in this case.

[Flags]
public enum ResultStatusEnum
{
    Ok = 0x1,
    SampleInvalid = 0x2,
    DirectionInvalid = 0x4,
    TestIsNotValid = 0x8
}

You set it like this:

ResultStatusEnum res = ResultStatusEnum.SampleInvalid | ResultStatusEnum.DirectionInvalid;

The disadvantage is that checking the values of the enum becomes cumbersome. This won't (necessarily) work:

res == ResultStatusEnum.Ok

You have to do this to check:

ResultStatusEnum.SampleInvalid == (res & ResultStatusEnum.SampleInvalid)

In this case, its illogical to have ResultStatusEnum.Ok & ResultStatusEnum.SampleInvalid, but I just make sure this isn't the case where I use the enum.