英文:
Type variables in Go
问题
在Haskell中，map的类型是：
map :: (a -> b) -> [a] -> [b]
请注意，a和b不是具体的类型，而是类型变量，这意味着它们可以是任何类型，只要在特定的函数调用中每个变量始终引用相同的类型。在Go语言中如何实现相同的功能呢？
英文:
In Haskell, map has type:
map :: (a -> b) -> [a] -> [b]
Note that a and b are not absolute types but type variables, which mean that they can be any type as long as each variable always refer to the same type in a specific function call. How to do the same thing in Go?
答案1
得分: 6
Go语言没有像Haskell那样的Hindley-Milner类型系统，所以它不能完全表达相同的东西，比如带有变量的类型。在Go中，实现类型不可知的函数是通过接口来实现的。如果你想表示"任意类型"，通常会写成一个空接口(interface{})。标准库中Map函数的类型是：
func Map(iter Iterable, f func(interface{}) interface{}) Iterable
所以，它接受的不是一个从a到b的函数，而是一个从interface{}到interface{}的函数。
英文:
Go does not have a Hindley-Milner type system like Haskell's, so it can't express exactly the same things, like types with variables. The way type-agnostic functions are done in Go is with interfaces. If you want to express "any type", that's usually written as an empty interface (interface{}). The type of the Map function in the standard library is:
func Map(iter Iterable, f func(interface{}) interface{}) Iterable
So instead of taking a function that goes from a to b, it takes a function that goes from interface{} to interface{}.
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