Enum flag patterns

[oriko1010]

I often find myself writing similar patterns with flag enums where certain flags take precedence

direction switch
{
    _ when direction.HasFlag(Direction.Up) => ...,
    _ when direction.HasFlag(Direction.Down) => ...,
    Direction.Left => ...,
    Direction.Right => ...,
};

It would be really convenient to have a flag constant-expression pattern to match such cases (exact syntax doesn't matter).

direction switch
{
    flag Direction.Up => ...,
    flag Direction.Down => ...,
    flag Direction.Left => ...,
    flag Direction.Right => ...,
};

Has there been any discussion on this? I wouldn't mind trying to write a proposal or maybe even attempt an implementation if this is something desirable.

[YairHalberstadt]

This does seem interesting, but I'm not sure how practically useful it is:

With flags, you generally want to handle all flags.
In a switch you can only handle one case.
So I'm not sure how often you would actually switch on flags.

In practice in your case for example I would imagine you want to handle all these cases separately:

0
Up
Down
Left
Right
Up Left
Up Right
Down Left
Down Right

flags wouldn't be approriate for this, whilst a normal switch on enum values would.

[alrz]

With #1047 I could image you'd be able to do something like that

static bool Flag(this Direction self, Direction d) => self.HasFlags(d); // hypothetical "pattern extensions"

direction switch
{
 Flag(Direction.Up) => ...,
 Flag(Direction.Down) => ...,
}

[oriko1010]

Perfect, that's good enough.