具有靜態約束的泛型類型的F＃單例

Question

我想知道是否可以為具有靜態約束的泛型類型創建單例（以下第三個類型將無法編譯）。 inline添加到第三種類型的成員不起作用。 非常感謝！

type A private () = 
    static let instance = A ()
    static member Instance = instance
    member this.DoNothing (x : int) = 0


type GenericA<'B> private () =
    static let instance = GenericA<'B> ()
    static member Instance = instance
    member this.DoNothing (x : 'B) = 0


type GenericWithStaticConstraintA<'B when 'B : (static member MyMember : Unit -> int)> private () =
    static let instance = GenericWithStaticConstraintA<'B> ()
    static member Instance = instance
    member this.DoNothing (x : 'B) = 0

Answer 1

您可以通過inline關鍵字在靜態成員的類上使用靜態解析的類型約束。

type GenericWithStaticConstraintA< ^B when ^B : (static member MyMember : unit -> int)> =
    static member inline DoNothing(x : ^B) = 0

例：

type Foo = Foo with static member MyMember() = 42
type Bar = Bar with static member MyMember = fun () -> 42
GenericWithStaticConstraintA.DoNothing(Foo)
GenericWithStaticConstraintA.DoNothing(Bar) // The type 'Bar' does not support the operator 'MyMember'

您也可以使用實例成員（ member inline __.DoNothing(x : ^B) = 0 ）來執行此操作，但是這樣做的目的是什么？