具有构造签名的接口如何工作? [英] How does interfaces with construct signatures work?

问题描述

我在弄清楚接口中定义构造函数的工作方式时遇到了一些麻烦.我可能完全误解了一些东西.但是我已经搜索了很长时间的答案，但找不到与此相关的任何内容.

I am having some trouble working out how defining constructors in interfaces work. I might be totally misunderstanding something. But I have searched for answers for a good while and I can not find anything related to this.

如何在 TypeScript 类中实现以下接口:

How do I implement the following interface in a TypeScript class:

interface MyInterface {
    new ( ... ) : MyInterface;
}

Anders Hejlsberg 在此视频中创建了一个包含类似内容的界面(大约 14 分钟).但是对于我的一生，我无法在课堂上实现这一点.

Anders Hejlsberg creates an interface containing something similar to this in this video (at around 14 minutes). But for the life of me I can not implement this in a class.

我可能误解了一些东西，我没有得到什么?

I am probably misunderstanding something, what am I not getting?

澄清一下.新(...)"我的意思是任何东西".我的问题是我什至无法获得此工作的最基本版本:

To clarify. With "new ( ... )" I meant "anything". My problem is that I can not get even the most basic version of this working:

interface MyInterface {
    new () : MyInterface;
}

class test implements MyInterface {
    constructor () { }
}

这不是为我编译我在尝试编译时得到类'test'声明接口'MyInterface'但没有实现它:类型'MyInterface'需要一个构造签名，但类型'test'缺少一个".

This is not compiling for me I get "Class 'test' declares interface 'MyInterface' but does not implement it: Type 'MyInterface' requires a construct signature, but Type 'test' lacks one" when trying to compile it.

因此，根据反馈，在对此进行了更多研究之后.

So after researching this a bit more given the feedback.

interface MyInterface {
    new () : MyInterface;
}

class test implements MyInterface {
    constructor () => test { return this; }
}

不是有效的 TypeScript，这不能解决问题.您不能定义构造函数的返回类型.它将返回测试".签名如下:类测试{构造函数 () { }}似乎是new () => test"(通过将鼠标悬停在仅粘贴该代码的在线编辑器中的class"上获得).这就是我们想要的，也是我认为的.

Is not valid TypeScript and this does not solve the problem. You can not define the return type of the constructor. It will return "test". The signature of the following: class test { constructor () { } } Seems to be "new () => test" (obtained by hovering over "class" in the online editor with just that code pasted in). And this is what we would want and what i thought it would be.

任何人都可以提供一个实际编译的例子或类似的东西吗?

Can anyone provide an example of this or something similar where it is actually compiling?

编辑(再次...):

所以我可能想出了一个想法，为什么可以在接口中定义它，但不能在 TypeScript 类中实现.以下工作:

So I might have come up with an idea as to why it is possible to define this in an interface but not possible to implement in a TypeScript class.The following works:

var MyClass = (function () {
    function MyClass() { }
    return MyClass;
})();

interface MyInterface {
    new () : MyInterface;
}

var testFunction = (foo: MyInterface) : void =>  { }
var bar = new MyClass();
testFunction(bar);

那么这只是 TypeScript 的一项功能，可以让您与 javascript 交互吗?或者是否可以在 TypeScript 中实现它而不必使用 javascript 实现类?

So is this only a feature of TypeScript that lets you interface javascript? Or is it possible to implement it in TypeScript without having to implement the class using javascript?

推荐答案

接口中的构造签名不能在类中实现；它们仅用于定义定义新"功能的现有 JS API.这是一个涉及接口 new 签名的例子，它确实有效:

Construct signatures in interfaces are not implementable in classes; they're only for defining existing JS APIs that define a 'new'-able function. Here's an example involving interfaces new signatures that does work:

interface ComesFromString {
    name: string;
}

interface StringConstructable {
    new(n: string): ComesFromString;
}

class MadeFromString implements ComesFromString {
    constructor (public name: string) {
        console.log('ctor invoked');
    }
}

function makeObj(n: StringConstructable) {
    return new n('hello!');
}

console.log(makeObj(MadeFromString).name);

这为您可以调用 makeObj 的内容创建了一个实际约束:

This creates an actual constraint for what you can invoke makeObj with:

class Other implements ComesFromString {
    constructor (public name: string, count: number) {
    }
}

makeObj(Other); // Error! Other's constructor doesn't match StringConstructable

这篇关于具有构造签名的接口如何工作?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！