Initial draft of Flags Enum Operators proposal.

[AdamSpeight2008]

Potential solution for #228
Proposal for Flags Enum Operators.

[franzalex]

Much as I like [and appreciate] the work that this is receiving, I think that using the extension methods (after a relaxation of the generic type parameter rules to allow Enums) is more readable. Better still, this could be built into the Framework itself instead of using extension methods.

I find the code below to be more readable

Dim someColor As Flags
someColor.Set(Flags.Red)
someColor.Set(Flags.Green)

If Not someColor.IsSet(Flags.Blue) Then
    ' do something
End If

It may be verbose, but it the intent is clearer. Plus, it ties in better with other similar implementations such as Jon Skeet's UnconstranedMelody and Tyler Brinkley's Enums.NET.

Note as well that the latter developer is even trying to get some of Enums.NET's improvements into corefx in this proposal which has gained quite a lot of traction. So my opinion is that we try to make design this to look and work similarly rather than coming up with new and potentially obscure operators.

My two cents.

[AdamSpeight2008]

@franzalex I see them as complimentary, the corefx proposal cover the framework api. This covers a possible language support. Akin to ValueTyples

I think have a language feature, we could do a form of constant folding on the setting and clearing of flags.

[AdamSpeight2008]

Screenshot of how it looks

The states!Blue = True assignment targeting isn't supported, has I not yet looked at how to implement it. Supported states!Red '(IsSet), states!+Red ' (Set Flag) and states!-Red '(Clear Flag)

[ghost]

@franzalex
I agree. I said something like that in:
#228 (comment)
I don't like the !+ and !- sympoles.

[AdamSpeight2008]

Comparisions

Quick Token Accumulator
Currently
Using Feature

SynthesizedMethod.vb
Currently
Using Feature

[gafter]

@AdamSpeight2008 The first step in designing a language feature is to open an issue on the vblang repository requesting or proposing the feature where it can be discussed by the community and the LDM. If and when the LDM believes it has converged on a language approach to the problem identified (note that the LDM starts by considering the problem to be solved), then (and only then) it makes sense to add a specification draft. This PR is premature.

[AdamSpeight2008]

@gafter I did is in in #228

[AdamSpeight2008]

As proposed the ! IsSet operator, is treated as are all these flags set.
Should we also support are any of these flags set ?

[gafter]

#228 does not indicate that the LDM decided on this form of a language feature for the problem.

[AdamSpeight2008]

I'm considering implementing

• !/ as the IsAnyFlagSet binary operator.
• extending the flag part to include ParenthesiesExpressions as well
  • As it will allow passing a variable identifier as the argument on the right.
  • Dim HasRedAndGreenFlag As Boolean = enumFlags ! ( Flags.Red !+ Flags.Green )
  • Dim HasRedOrGreenFlag As Boolean = enumFlags !/ ( Flags.Red !+ Flags.Green )

[AdamSpeight2008]

Note to self: Update the specification

[AdamSpeight2008]

The following branch has an experimental prototype implementation. stable but don't use on anything vital
Prototypes/VB_EnumFlagExpression