如何获得具有可变数量参数的整数元组的产品？

Question

type TotalSizeToken = TotalSizeToken with 
    static member TotalSize(_: TotalSizeToken, (a,b,c,d,e)): int = a*b*c*d*e 
    static member TotalSize(_: TotalSizeToken, (a,b,c,d)): int = a*b*c*d 
    static member TotalSize(_: TotalSizeToken, (a,b,c)): int = a*b*c 
    static member TotalSize(_: TotalSizeToken, (a,b)): int = a*b 
    static member TotalSize(_: TotalSizeToken, x: int): int = x 

let inline size_to_total_size x = 
    ((^s) : (static member TotalSize: TotalSizeToken * ^s -> int) TotalSizeToken, x) 

let t = size_to_total_size (1,5) // Error: Expecting a type supporting the operator TotalSize, but given a tuple type. 

我没有想到size_to_total_size中的x参数需要TotalSize成员。这感觉就像一个编译器错误。

我不知道如何让这个工作。有任何想法吗？

Answer 1

你错过了其他的“帽子”类型：

let inline size_to_total_size x = 
    let call (t:^T) = ((^s or ^T) : (static member TotalSize: TotalSizeToken * ^s -> int) t, x) 
    call TotalSizeToken 

必须有两个人，正在传递的参数，并表示包含重载类中的一个。

否则，它不会查看类，只能在元组中找到，而元组类型中没有这样的方法。

Answer 2

type TotalSizeToken<'u> = TotalSizeToken of 'u with 
    static member TotalSize(x: TotalSizeToken<int*int*int*int*int>): int = 
     match x with TotalSizeToken (a,b,c,d,e) -> a*b*c*d*e 
    static member TotalSize(x: TotalSizeToken<int*int*int*int>): int = 
     match x with TotalSizeToken (a,b,c,d) -> a*b*c*d 
    static member TotalSize(x: TotalSizeToken<int*int*int>): int = 
     match x with TotalSizeToken (a,b,c) -> a*b*c 
    static member TotalSize(x: TotalSizeToken<int*int>): int = 
     match x with TotalSizeToken (a,b) -> a*b 
    static member TotalSize(x: TotalSizeToken<int>): int = 
     match x with TotalSizeToken x -> x 

let inline size_to_total_size x = 
    ((^s) : (static member TotalSize: ^s -> int) x) 

let t = size_to_total_size (TotalSizeToken(1,5)) 

这种替代形式的作品。有一些额外的拳击，但从好的方面来说，我不需要到处传递lambda。奇怪的是，如果size_to_total_size被写为let inline size_to_total_size x = ((^s) : (static member TotalSize: TotalSizeToken< ^s> -> int) x)，那么它不起作用。