打字稿“这种打字"困惑 [英] Typescript "this-typing" confusion

问题描述

我指的是在这里，以及此处.

据我所知，使用 this 作为类型是指当前类，或点剩下的任何内容(从而允许继承的方法引用它们自己的类而不是它们父类的类).

It is my understanding that using this as a type refers to the current class, or whatever is left of the dot (thereby allowing inherited methods to refer to their own class instead of their parent's class).

那么有人可以解释为什么这不起作用:

So can someone explain why this doesn't work:

class Test {
    children: Array<this>;

    constructor() {
        this.children = [new Test()];
    }
}

(我的目标是使用继承的类来实现，但它不适用于基类.既然 this 是 Test 类型，为什么不能children 是 Test 的数组吗?

(My goal is to do that with an inherited class, but it doesn't work with a base class. Since this is of type Test why can't children be an array of Test?

推荐答案

不，当使用 this 作为类型时，您指的是实例而不是类.
它被称为 多态这种类型，意思是像这样使用:

No, when using this as a type you are referring to the instance and not the class.
It's called Polymorphic this types and is meant to be used like this:

class Point {}

class Point2D extends Point {
    constructor(public x: number, public y: number) {
        super();
    }
}

class Point3D extends Point2D {
    constructor(x: number, y: number, public z: number) {
        super(x, y);
    }
}

class Builder2D {
    protected _x: number;
    protected _y: number;

    x(x: number): this {
        this._x = x;
        return this;
    }

    y(y: number): this {
        this._y = y;
        return this;
    }

    build(): Point {
        return new Point2D(this._x, this._y);
    }
}

class Builder3D extends Builder2D {
    private _z: number;

    z(z: number): this {
        this._z = z;
        return this;
    }

    build(): Point3D {
        return new Point3D(this._x, this._y, this._z);
    }
}

let p1 = new Builder3D().x(0).y(0).z(0).build();

(操场上的代码)

如果 Builder2D.x() 和 Builder2D.y() 会返回 Builder2D:

If Builder2D.x() and Builder2D.y() would have returned Builder2D:

x(x: number): Builder2D {
    this._x = x;
    return this;
}

y(y: number): Builder2D {
    this._y = y;
    return this;
}

那么这将失败:

let p1 = new Builder3D().x(0).y(0).z(0).build();

与:

属性 'z' 不存在于类型 'Builder2D'

Property 'z' does not exist on type 'Builder2D'

在您的情况下，情况并非如此，您不想返回 this.
据我所知，this 的类没有类型，但你可以这样做:

In your scenario this isn't the case, you don't want to return this.
As far as I'm aware there's no type for the class of this, but you can do:

class Test {
    public children: Array<Test>;

    constructor() {
        this.children = [new Test()];
    }
}

interface OtherTest {
    children: Array<OtherTest>;
}
class OtherTest extends Test {
    constructor() {
        super();
        this.children.push(new Test(), new OtherTest());
    }
}

let t1 = new Test();
let c1 = t1.children[0]; // typeof c1 is Test

let t2 = new OtherTest();
let c2 = t2.children[0]; // typeof c2 is OtherTest

(代码在操场上)

似乎有一个问题:静态成员的多态this".

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