f# - 如何将 OO 调用转换为一些通用函数调用

Question

我有以下代码

type Show<'a> =
    abstract member Show: 'a -> string

type Shows() = 
    member inline this.GetShow(x:string) = 
        {new Show<string> with member this.Show(x:string) = x}
    member inline this.GetShow(x:int) = 
        {new Show<int> with member this.Show(x:int) = sprintf "%A" x}

如果我使用普通的 OO 表示法调用它，它会完美地工作。

printfn "100 %s" (Shows().GetShow("some").Show("some"))

但是我想把它包装成一个函数，这样

let inline show x = (Shows().GetShow(x).Show(x))

但这给了我以下错误

[FS0041] A unique overload for method 'GetShow' could not be determined based 
on type information prior to this program point. A type annotation may be 
needed. Candidates: 
member Shows.GetShow : x:int -> Show<int>, 
member Shows.GetShow : x:string -> Show<string>

有什么办法可以克服这个问题吗？

Answer 1

这是否让您足够接近您想要的东西？

let inline GetShow p x = (^x : (member GetShow : ^p -> ^o) (x, p))
let inline Show p x = (^x : (member Show : ^p -> ^o) (x, p))

let inline show x s = s |> GetShow x |> Show x

Shows() |> show "a"
Shows() |> show 1

如果在内联函数之外创建Shows 并不难。这样方法就不需要内联。