F#位标志枚举

Question

我想在F#中创建一个bitflags枚举,使用bitshift运算符来提高可读性:例如

[<Flags>]
type DaysOfWeek =
    | Monday = 1 <<< 0
    | Tuesday = 1 <<< 1
    | Wednesday = 1 <<< 2
    | Thursday = 1 <<< 3
    | Friday = 1 <<< 4
    | Saturday = 1 <<< 5
    | Sunday = 1 <<< 6

但是,F#编译器不喜欢这个.它说"成员定义中的意外中缀运算符".

我希望这种方法超过两种手动权限.有没有办法说服编译器我不是邪恶的？

Answer 1

这不完全是你要求的,但你可以使用0b前缀来编写二进制长手,例如:

[<Flags>]
type DaysOfWeek =
    | Monday    = 0b0000001
    | Tuesday   = 0b0000010
    | Wednesday = 0b0000100
    | Thursday  = 0b0001000
    | Friday    = 0b0010000
    | Saturday  = 0b0100000
    | Sunday    = 0b1000000

Answer 2

将案例与值分开的替代方法，更冗长但更灵活：

type DaysOfWeek =
  | Monday
  | Tuesday
  | Wednesday
  | Thursday
  | Friday
  | Saturday
  | Sunday
  with
    static member Flag x =
      let bit n = 1 <<< n
      match x with
      | Monday ->    bit 0
      | Tuesday ->   bit 1
      | Wednesday -> bit 2
      | Thursday ->  bit 3
      | Friday ->    bit 4
      | Saturday ->  bit 5
      | Sunday ->    bit 6

Answer 3

这是 Dave Fancher 在The Book of F#中推荐的方法

使用值为 2 的幂的 Flags 属性：

open System

[<Flags>]    
type DayOfWeek =
  | None = 0
  | Sunday = 1
  | Monday = 2
  | Tuesday = 4
  | Wednesday = 8
  | Thursday = 16
  | Friday = 32
  | Saturday = 64

Flags 属性不是必需的，但可以明确您的意图。

您现在可以使用按位运算符表示值的组合：

let weekend = DayOfWeek.Saturday ||| DayOfWeek.Sunday