javascript - typescript 等于

Question

如何在 Typescript 中实现 equals？
我尝试了几种方法，都没有奏效。

选项1:

abstract class GTreeObject<T>{ 
    abstract equals(obj: T): boolean; 
} 

class GNode extends GTreeObject<GNode>{ 
    public equals(obj: GNode){ 
        //Implement 
    } 
} 

结果:通用类型“GNode”需要 1 个类型参数。

选项 2 将涉及在运行时进行强制转换，但如何进行强制转换？:

abstract class GTreeObject{ 
    abstract equals(obj: Object): boolean; 
} 

class GNode extends GTreeObject{ 
    //How to cast Object to GNode?? 
    public equals(obj: Object){ 
        //Implement 
    } 
} 

如何可靠解决？

Answer 1

根据 TypeScript 游乐场，唯一的问题是您忘记声明 equals 实现的返回类型在 GNode :

abstract class GTreeObject<T>{ 
    abstract equals(obj: T): boolean; 
} 

class GNode extends GTreeObject<GNode>{ 
    public equals(obj: GNode) : boolean { 
    // ----------------------^^^^^^^^^^
        return /*implementation*/true;
    } 
}

这个完整的例子有效，例如:

abstract class GTreeObject<T>{ 
    abstract equals(obj: T): boolean; 
} 

class GNode extends GTreeObject<GNode>{
    private value: number;

    public constructor(value: number) {
        super();
        this.value = value;
    }
    public equals(obj: GNode) : boolean { 
        return this.value === obj.value;
    } 
} 

let g1 : GNode = new GNode(42);
let g2 : GNode = new GNode(42);
let g3 : GNode = new GNode(27);
console.log(g1.equals(g2)); // true
console.log(g1.equals(g3)); // false

回复您的评论:

Sorry for the hassle. This seems to work for GNode, but when implementing GTree:

class GTree<T> extends GTreeObject<GTree>

this seems to result in an error: Generic type 'GTree' requires 1 type argument(s). Is there a problem using two generic types in the class definition (taking + passing a generic)?

您需要将类型参数声明为 GTreeObject如 GTree<T> ，而不仅仅是 GTree :

class GTree<T> extends GTreeObject<GTree<T>> {
// -------------------------------------^^^
    public equals(obj: GTree<T>) : boolean { 
    // ---------------------^^^
        return /*implementation*/true;
    } 
}