打字稿错误地将元组推断为数组 [英] Typescript inferring Tuple as Array Incorrectly

问题描述

先为我的英语道歉.

我有一个类似 function func(): [string, string[]] 的函数，它返回一个元组.但是，当我实现像

I have a function like function func(): [string, string[]] which returns a Tuple. However, when I implement the return statement like

var test = ['text', ['foo', 'bar']];
return test;

Typescript 将我的返回类型推断为 (string | string[])[] 而不是 [string, string[]].

Typescript inferred my return type as (string | string[])[] instead of [string, string[]].

我是否遗漏了什么，或者我是否需要每次都将返回对象显式转换为元组，例如 return <[string, string[]]>['text', ['foo', 'bar']].如果是，那不是很烦人吗?

Did I missed something or should I need to cast the return object as Tuple explicitly everytime like return <[string, string[]]>['text', ['foo', 'bar']]. If yes then isn't it quite annoying?

提供的完整功能如下:

function func(): [string, string[]] {
    var test= ['text', ['foo', 'bar']];

    return test;
}

错误:类型 '(string | string[])[]' 缺少类型 '[string, string[]]' 的以下属性:0, 1ts(2739)

推荐答案

TS 无法区分，如果你想让 ['text', ['foo', 'bar']] 成为 <一个 href="https://www.typescriptlang.org/docs/handbook/basic-types.html#array" rel="nofollow noreferrer">array 或一个 tuple - 表达式 是一样的！如果没有其他指定，它将默认为 test 变量类型的数组.

TS cannot differentiate, if you want ['text', ['foo', 'bar']] to be an array or a tuple - the expression is the same! It will default to an array for the test variable type, if nothing else specified.

如果您想要一个元组，请执行以下操作之一:

If you want a tuple, do one of the following:

• 使用 const 断言
• 给 test 一个显式的元组类型

• use a const assertion
• give test an explicit tuple type

function func(): [string, string[]] {
    const test = ['text', ['foo', 'bar']];
    const test2 = ['text', ['foo', 'bar']] as const;
    const test3: [string, string[]] = ['text', ['foo', 'bar']];
    // return test;   // error, was inferred as array
    // return test2; // works
    return test3; // works
}

使用 as const 你不必重复你的类型，但你必须用 readonly 修饰符来注释函数返回类型: readonly [string, 只读 [string, string]].

With as const you don't have to repeat your type, but you will have to annotate the function return type with readonly modifiers: readonly [string, readonly [string, string]].

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