用尖括号“<>"将类括起来是什么意思?在打字稿中是什么意思? [英] What does enclosing a class in angle brackets "<>" mean in TypeScript?

问题描述

我对 TypeScript 非常陌生，我非常喜欢它，尤其是在 Javascript 中执行 OOP 是多么容易.然而，在使用尖括号时，我一直试图弄清楚语义.

I am very new to TypeScript and I am loving it a lot, especially how easy it is to do OOP in Javascript. I am however stuck on trying to figure out the semantics when it comes to using angle brackets.

从他们的文档中，我看到了几个像

From their docs, I have seen several examples like

interface Counter {
  (start: number): string;
  interval: number;
  reset(): void;
}

function getCounter(): Counter {
  let counter = <Counter>function (start: number) { };
  counter.interval = 123;
  counter.reset = function () { };
  return counter;
}

和

interface Square extends Shape, PenStroke {
  sideLength: number;
}
  
let square = <Square>{};

我无法理解这究竟意味着什么或思考/理解它的方式.

I am having trouble understanding what this exactly means or the way to think of/understand it.

谁能给我解释一下?

推荐答案

这就是所谓的 输入断言 或强制转换.

That's called Type Assertion or casting.

这些都是一样的:

let square = <Square>{};
let square = {} as Square;

示例:

interface Props {
    x: number;
    y: number;
    name: string;
}

let a = {};
a.x = 3; // error: Property 'x' does not exist on type `{}`

所以你可以这样做:

let a = {} as Props;
a.x = 3;

或者:

let a = <Props> {};

哪个会做同样的

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