TypeScript泛型函数的类型 [英] TypeScript Type of generic function

问题描述

我无法理解TypeScript文档中的以下段落:

I can't get my head arround the following paragraph in the TypeScript documentation:

泛型函数的类型与非泛型函数的类型相似，首先列出类型参数，类似于函数声明:"

"The type of generic functions is just like those of non-generic functions, with the type parameters listed first, similarly to function declarations:"

function identity<T>(arg: T): T {
    return arg;
}

let myIdentity: <T>(arg: T) => T = identity;

最后一行是做什么的，为什么要使用它?

What does the last line do and why is it used?

据我了解，myIdentity是获取身份函数类型的变量?如果是这种情况，为什么我需要定义这样的变量?函数标识已经声明了我可以期望的返回类型.

As far as I understood, myIdentity is a variable which gets the type of the identity function? And if this is the case why do I need to define such a variable? The function identity already declares what return type I can expect.

推荐答案

最后一行声明一个名为myIdentity的变量.变量属于函数类型，是泛型函数(<T>使它成为泛型函数的签名，列表中可能包含更多类型实参)，该变量接受类型为T的实参并返回类型的值T.然后使用identity函数初始化变量，该函数符合myIdentity声明的签名.

The last line declares a variable named myIdentity. The variable is of a function type, a generic function (the <T> makes the it the signature of a generic function, more type arguments could be in the list) which takes an argument of type T and returns a value of typeT. And then initializes the variable with the identity function which conforms to the declared signature of myIdentity.

您可能需要执行此操作，以便根据运行时条件为myIdentity分配不同的功能.或声明此类型的参数，并将其传递给以后可以调用它的函数.

You may want to do this in order to assign different functions to myIdentity based on runtime conditions. Or declare a parameter of this type and pass it to a function that can invoke it later.

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