使用元组对抽象类型进行类型推断 [英] type inference on abstract type with a tuple

问题描述

基于此 kvb的答案，此代码进行了编译(F#4 )并运行:

Based on this kvb's answer, this code compiles (F#4) and runs :

type Untupler = abstract Apply : 'u * 'u -> 'u

let myotherFun arg1 arg2 =
    printfn "myotherFun result is : %A %A" arg1 arg2

let myFunction tup1 tup2 (i:Untupler) =
    myotherFun (i.Apply tup1) (i.Apply tup2)

let reskvb = myFunction (1,2) ("Hello","World") { new Untupler with member __.Apply (x,y) = snd (x,y) }

但是如果最后一行替换为初始答案:

But if the last line is replaced by the initial answer :

let reskvb = myFunction (1,2) ("Hello","World") { new Untupler with member __.Apply x = fst x }

然后，编译器抱怨FS0768错误: 成员"Apply"不接受正确数量的参数，预计需要2个参数

then the compiler complains with error FS0768 : The member 'Apply' does not accept the correct number of arguments, 2 arguments are expected

我不明白为什么编译器似乎无法推断x确实是一个元组.还是我还缺少另一个问题?谢谢.

I do not understand why the compiler seems to fail to infer that x is indeed a tuple. Or is there another issue I am missing ? Thx.

推荐答案

这样做的原因是，当您开始使用接口时，您会进入F#对面向对象编程的支持，而在F#中，所有 OOP互操作方法默认为元组.

The reason for this is that when you start using interfaces, you move into F#'s support for Object-Oriented Programming, and in F#, all OOP interop methods are tupled by default.

因此，Apply方法被解释为带有两个方法参数的方法，而不是一个带有单个元组作为输入的函数.

Thus, the Apply method is interpreted as being a method that takes two method arguments, rather than a function that takes a single tuple as input.

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