Functions Overloading in interface and classes - how to?

Question

I have this interface :

interface IPoint {
    getDist(): string;
    getDist(x: number): any;
}

and I need a class to implement it but I can't get the right syntax to implement the getDist() method in the class..

class Point implements IPoint {
    // Constructor
    constructor (public x: number, public y: number) { }

    pointMethod() { }

    getDist() {
        Math.sqrt(this.x * this.x + this.y * this.y);
    }
    // Static member
    static origin = new Point(0, 0);
}

it says:

Class 'Point' declares interface 'IPoint' but does not implement it: Types of property 'getDist' of types 'Point' and 'IPoint' are incompatible:Call signatures of types '() => void' and '{ (): string; (x: number): any; }' are incompatible

What's the proper way to do this?

Thanks

score 7 · Accepted Answer · answered Nov 04 '12 at 14:34

7

When you declare the function in the class you need to decorate it with the overloads:

getDist(): string;
getDist(x: number): any;
getDist(x?: number): any {
    // your code
 }

answered Nov 04 '12 at 14:34

Fenton

241,084
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You need not write the second declaration. It works even without that – S. Ravi Kiran Nov 05 '12 at 20:37
@S.RaviKiran you need both overload declarations as you can't call the implementation on overloaded functions. You can try this out in the TypeScript Playground. http://www.typescriptlang.org/Playground/ – Fenton Nov 06 '12 at 08:20
@S.RaviKiran Post your example. – Fenton Nov 06 '12 at 14:13
2

it works without adding the declarations but to get overloading in Visual studio auto complete you need to add overloading decelerations. – Bashar Ali Labadi Nov 08 '12 at 08:02
And static typing for the return values, which are different. – Fenton Nov 08 '12 at 09:25

score 5 · Answer 2 · edited May 23 '17 at 12:16

This answer describes how to implement method overloading in TypeScript, and it's not pretty:

interface IPoint {
    getDist(): string;
    getDist(x: number): any;
}

class Point implements IPoint {
    // Constructor
    constructor (public x: number, public y: number) { }

    pointMethod() { }

    getDist(x?: number) {
         if (x && typeof x == "number") {
             return 'foo';
         } else {
             return 'bar';
         }
    }
}

N.B. with the particular combination of declared return types in the interface, you are limited to returning strings from getDist.

You mean it's not pretty just because it has the if-else typeguards? — 1252748, Apr 21 '21 at 16:55

Pax Exterminatus · Answer 3 · 2019-11-16T11:32:57.657

2

also you can use the default value

interface Foo{
    next()
    next(steps: number)
    prev()
    prev(steps: number)
}

next(steps: number = 1) {
    // ...
}

prev(steps: number = 1) {
    // ...
}

edited Nov 16 '19 at 11:32

answered Nov 16 '19 at 11:23

Pax Exterminatus

504
4
9

score 0 · Answer 4 · edited Nov 09 '18 at 17:56

The following is a variation on some of the above

class Position {
    x: number;
    y: number;

    constructor(x : number = 0, y : number = 0) {
        this.x = x;
        this.y = y;
    }    
}

class Pen {
    colour: string;

    constructor(colour: string) {
        this.colour = colour;
    }
}

class PlottingHead {
    isPenUp: boolean;
    pen: Pen;
    position: Position;

    constructor() {     
       this.penUp();
   }

   move(p: Position): void;
   move(x: number, y: number): void;
   move(x: number | Position, y?: number): void {
        if (typeof x === "number")
        {
            x = new Position(x, y);
        }
        this.penUp();
        this.position = x;
    }

    draw(x: number | Position, y?: number): void {
        if (typeof x === "number")
        {
            x = new Position(x, y);
        }
        this.penDown();
        this.position = x;
    }

    penDown(): void {
        this.isPenUp = false;
     }

    penUp(): void {
        this.isPenUp = true;
    }

    onChangePen(newPen: Pen) {
        this.penUp();
        this.pen = newPen;
    }    
}

The move function takes either a single position object or a pair of numeric values. This can obviously be extended as required.

Functions Overloading in interface and classes - how to?

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