Question

我想创建一些类似于带有F＃记录类型的枚举的东西，而不是int。例如，如果我有工会：

type BologneseIngredients = | Spaghetti
                            | Tomatoes
                            | MincedBeef
                            | GrandmasSecretIngredient

我知道意大利面总是长30厘米，西红柿总是红的。我能做的是拥有'获取元数据'功能：

let getMetadata = function
                    | Spaghetti -> { length: 30.0<cm> }
                    | Tomatoes -> { colour: Color.Red }
                    | _ -> { }

但我真的想将联合和数据的定义保持在一起。有没有一个很好的方法来做到这一点？

Answer 1

您可以为受歧视的联盟添加属性......

type BologneseIngredients = 
    | Spaghetti
    | Tomatoes
    | MincedBeef
    | GrandmasSecretIngredient

    member x.Color =
        match x with
        | Spaghetti -> Color.AntiqueWhite
        | Tomatoes -> Color.Red
        | MincedBeef -> Color.Firebrick
        | GrandmasSecretIngredient -> Color.Transparent



let foo = Tomatoes

printfn "%A" foo.Color

> Color [Red]

Answer 2

我的建议：

module Recipes =

    type BologneseIngredients = | Spaghetti
                                | Tomatoes
                                | MincedBeef
                                | GrandmasSecretIngredient

    let length (ind : BologneseIngredients) : float<cm> option =
         match ind with
         | Sphaghetti -> Some 30.0<cm>
         | _ -> None

    // .. or a bit more "metadata"ish
    type Metadata = 
        | Length of float<cm>
        | Color of System.Drawing.Color

    let metadata = 
       function
       | Sphaghetti -> [ Length 30.0<cm ]
       | Tomatoes   -> [ Color System.Drawing.Color.Red ]
       | ...

    let metaLength meta =
       meta |> List.tryPick (function | Length l -> Some l | _ -> None)

    let getLength = metadata >> metaLength

在F＃中，如何将元数据附加到区分联合值？

2 个答案: