F#元组的扩展方法 [英] Extension methods for F# tuples

问题描述

是否可以为F#元组编写扩展方法?例如，要添加实例方法.Item1和.Item2(如System.Tuple)，它们等效于为2元组调用fst和snd?

Is it possible to write extension methods for F# tuples? For example, to add instance methods .Item1 and .Item2 (like System.Tuple) which are equivalent to calling fst and snd for 2-tuples?

推荐答案

虽然不完美，但我正在使用它. (我从 http://www.fssnip.net/6V 借用了原始代码，并做了一些小的修改.)

Not perfect but I'm using this. (I borrowed original code from http://www.fssnip.net/6V and added small modification.)

[<AutoOpen>]
module TupleExtensions =
  type System.Tuple with
    static member Item1(t) = let (x,_) = t in x
    static member Item1(t) = let (x,_,_) = t in x
    static member Item1(t) = let (x,_,_,_) = t in x
    static member Item1(t) = let (x,_,_,_,_) = t in x
    static member Item1(t) = let (x,_,_,_,_,_) = t in x
    static member Item1(t) = let (x,_,_,_,_,_,_) = t in x

    static member Item2(t) = let (_,x) = t in x
    static member Item2(t) = let (_,x,_) = t in x
    static member Item2(t) = let (_,x,_,_) = t in x
    static member Item2(t) = let (_,x,_,_,_) = t in x
    static member Item2(t) = let (_,x,_,_,_,_) = t in x
    static member Item2(t) = let (_,x,_,_,_,_,_) = t in x

    static member Item3(t) = let (_,_,x) = t in x
    static member Item3(t) = let (_,_,x,_) = t in x
    static member Item3(t) = let (_,_,x,_,_) = t in x
    static member Item3(t) = let (_,_,x,_,_,_) = t in x
    static member Item3(t) = let (_,_,x,_,_,_,_) = t in x

    static member Item4(t) = let (_,_,_,x) = t in x
    static member Item4(t) = let (_,_,_,x,_) = t in x
    static member Item4(t) = let (_,_,_,x,_,_) = t in x
    static member Item4(t) = let (_,_,_,x,_,_,_) = t in x

    static member Item5(t) = let (_,_,_,_,x) = t in x
    static member Item5(t) = let (_,_,_,_,x,_) = t in x
    static member Item5(t) = let (_,_,_,_,x,_,_) = t in x

    static member Item6(t) = let (_,_,_,_,_,x) = t in x
    static member Item6(t) = let (_,_,_,_,_,x,_) = t in x

    static member Item7(t) = let (_,_,_,_,_,_,x) = t in x  

如何使用它:

let t = (1, 2, 3)
let item1 = Tuple.Item1(t)

此处定义的

Tuple.Item1优于fst:它对项目数具有多态性.一旦使用这些扩展方法编写了使用n个元组的函数，就可以将其扩展为n + 1个元组，而无需修改函数体.相反，我们必须修改参数类型声明.更加轻松.

Tuple.Item1 defined here has advantage over fst: It is polymorphic for number of items. Once we write function which uses n tuple using these extension methods, we can extend it for n+1 tuple without modifying function body. Instead we have to modify argument type declaration. It is more effortless.

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