加宽：

Question

当我使用数组扩展运算符创建新数组时 TypeScript似乎丢失了正确的类型信息。

如果我使用Array.combine()创建新数组，则不会发生这种情况。

我准备了一个简单的例子来证明这一点。我使用声明合并使常量（ACES，TWOS等）具有相应的类型。然后我创建类型Category为＆＃34;超类型＆＃34;。

变量sectionsSpread在使用数组扩展运算符创建后属于string[]类型。变量sectionsCombined的类型为Category[]。

我预计变量sectionsSpread也属于Category[]类型。

这是一个错误吗？我有阵列传播错误吗？

const ACES = 'ACES';
type ACES = typeof ACES;

const TWOS = 'TWOS';
type TWOS = typeof TWOS;

const THREES = 'THREES';
type THREES = typeof THREES;

const FULL_HOUSE = 'FULL_HOUSE';
type FULL_HOUSE = typeof FULL_HOUSE;

const SMALL_STRAIGHT = 'SMALL_STRAIGHT';
type SMALL_STRAIGHT = typeof SMALL_STRAIGHT;

const LARGE_STRAIGHT = 'LARGE_STRAIGHT';
type LARGE_STRAIGHT = typeof LARGE_STRAIGHT;

type Category = ACES | TWOS | THREES |
    FULL_HOUSE | SMALL_STRAIGHT | LARGE_STRAIGHT;

const upperSection: Array<Category> = [ACES, TWOS, THREES];
const lowerSection: Array<Category> = [FULL_HOUSE, SMALL_STRAIGHT, LARGE_STRAIGHT]; 

const sectionsSpread = [
    ...upperSection,
    ...lowerSection
];

const sectionsCombined = upperSection.concat(lowerSection);

UDATE

@dbandstra和@basarat指出了我正确的方向。阅读suggested blog post后，我认为我理解文字类型扩展。但是，对于我来说，这仍然无法解释typeof运营商在此背景下的行为。

我希望以下示例能让我的问题更清晰：

const ACES = 'ACES';
type ACES = 'ACES'; // non-widening literal type 

const TWOS = 'TWOS';
type TWOS = 'TWOS'; // non-widening literal type

type Category = ACES | TWOS; // are these values or types?

const upperSection: Category[] = [ACES]; 
const lowerSection: Category[] = [TWOS];

const sectionsSpread = [
    ...upperSection,
    ...lowerSection,
]; // is of type Category[]

如果我使用typeof，则变量sectionsSpread最终会变为string[]类型：

const ACES = 'ACES';
type ACES = typeof ACES; // what does typeof do here?

const TWOS = 'TWOS';
type TWOS = typeof TWOS; // what does typeof do here?

type Category = ACES | TWOS; // are these values or types?

const upperSection: Category[] = [ACES]; 
const lowerSection: Category[] = [TWOS];

const sectionsSpread = [
    ...upperSection,
    ...lowerSection,
]; // is of type string[]

Answer 1

这是扩大与非扩大。显式注释意味着在分配给其他值时，TypeScript不会更改其含义。

加宽：

const ACES = 'ACES';
type Category = typeof ACES;

const upperSection: Category[] = []; 

const sectionsSpread = [
    ...upperSection,
]; // string[]

非扩展：

const ACES = 'ACES';
type Category = 'ACES';

const upperSection: Category[] = []; 

const sectionsSpread = [
    ...upperSection,
]; // Category

TypeScript（^ 2.3.3）是否会丢失有关数组传播的类型信息？

1 个答案:

加宽：

非扩展：