TypeScript 中的构造函数重载 [英] Constructor overload in TypeScript

问题描述

有人在 TypeScript 中做过构造函数重载吗?在语言规范 (v 0.8) 的第 64 页上，有描述构造函数重载的语句，但没有给出任何示例代码.

Has anybody done constructor overloading in TypeScript. On page 64 of the language specification (v 0.8), there are statements describing constructor overloads, but there wasn't any sample code given.

我现在正在尝试一个非常基本的类声明；看起来像这样，

I'm trying out a really basic class declaration right now; it looks like this,

interface IBox {    
    x : number;
    y : number;
    height : number;
    width : number;
}

class Box {
    public x: number;
    public y: number;
    public height: number;
    public width: number;

    constructor(obj: IBox) {    
        this.x = obj.x;
        this.y = obj.y;
        this.height = obj.height;
        this.width = obj.width;
    }   

    constructor() {
        this.x = 0;
        this.y = 0;
        this.width = 0;
        this.height = 0;
    }
}

当使用 tsc BoxSample.ts 运行时，它会抛出一个重复的构造函数定义——这很明显.任何帮助表示赞赏.

When ran with tsc BoxSample.ts, it throws out a duplicate constructor definition -- which is obvious. Any help is appreciated.

推荐答案

TypeScript 允许您声明重载，但您只能有一个实现，并且该实现必须具有与所有重载兼容的签名.在您的示例中，这可以使用可选参数轻松完成，如

TypeScript allows you to declare overloads but you can only have one implementation and that implementation must have a signature that is compatible with all overloads. In your example, this can easily be done with an optional parameter as in,

interface IBox {    
    x : number;
    y : number;
    height : number;
    width : number;
}

class Box {
    public x: number;
    public y: number;
    public height: number;
    public width: number;

    constructor(obj?: IBox) {    
        this.x = obj && obj.x || 0
        this.y = obj && obj.y || 0
        this.height = obj && obj.height || 0
        this.width = obj && obj.width || 0;
    }   
}

或两个具有更通用构造函数的重载，如，

or two overloads with a more general constructor as in,

interface IBox {    
    x : number;
    y : number;
    height : number;
    width : number;
}

class Box {
    public x: number;
    public y: number;
    public height: number;
    public width: number;

    constructor();
    constructor(obj: IBox); 
    constructor(obj?: any) {    
        this.x = obj && obj.x || 0
        this.y = obj && obj.y || 0
        this.height = obj && obj.height || 0
        this.width = obj && obj.width || 0;
    }   
}

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