Enum (flags) member composed of other members

问题:

[<Flags>]
type LikeMatch =
    | None  = 0
    | Start = 1
    | End   = 2
    | All   = Start ||| End //ERROR: Unexpected identifier in union case

I've also tried qualifying the members with the enum type. Is there a way to do this in F#?

回答1:

According to the F# language reference there is no way to do this. The right hand side of the = sign in a F# enum must be an integer literal

• http://msdn.microsoft.com/en-us/library/dd233216(v=VS.100).aspx

Grammar

type enum-name =
   | value1 = integer-literal1
   | value2 = integer-literal2

回答2:

As JaredPar says it's not allowed by the language, but F# does have binary literals which makes it easy to show which bits are being set:

open System

[<Flags>]
type LikeMatch =
    | None  = 0b000000000
    | Start = 0b000000001
    | End   = 0b000000010
    | All   = 0b000000011