Allow arithmetics on class/objects with valueOf method

[Zorgatone]

Both of the two examples below won't work, and I get a compiler error/warning: "The right-hand side of an arithmetic operation must be of type 'any', 'number' or an enum type.".

Example 1 (defining method valueOf and implementing Number interface) working on runtime:

class LOL implements Number {
    private _value: number;

    constructor(value) {
        this._value = value;
    }

    valueOf() {
        return this._value;
    }

    toFixed() {
        return Number.prototype.toFixed.call(this._value);
    }

    toExponential() {
        return Number.prototype.toExponential.call(this._value);
    }

    toPrecision() {
        return Number.prototype.toPrecision.call(this._value);
    }
}

type Lol = number | LOL;

let X: Lol = new LOL(10);
let Y: Lol = new LOL(7);

alert(X * Y);

Example 2 (extending Number "class") Runtime Error: "Uncaught TypeError: Number.prototype.valueOf is not generic"

class LOL extends Number {
    constructor(value) {
        super(value);
    }

    valueOf() {
        return super.valueOf();
    }

    toFixed() {
        return super.toFixed();
    }

    toExponential() {
        return super.toExponential();
    }

    toPrecision() {
        return super.toPrecision();
    }
}

type Lol = number | LOL;

let X: Lol = new LOL(10);
let Y: Lol = new LOL(7);

alert(X * Y);

[Zorgatone]

I also tried this one (defining a variable with the Number interface), and got the same right-hand side error message:

let X: Number = new LOL(10);
let Y: Number = new LOL(7);

alert(X * Y);

[Zorgatone]

I must define X,Y as any type, which is not the best thing to do 😞

[xLama]

This works on runtime but you can get a compiler error:

var x = new Number(10);
var y = new Number(20)

x * y 

I guess by design.

[Zorgatone]

@xLama yeah, of course. I was just experimenting with it, to see if there is a way to stop that compiler warning/error.

The other example works on runtime, but the TypeScript compiler complains about it

[xLama]

@Zorgatone But I don´t know why fails because ES lets it. Maybe a Microsoft employee can explain us. I think it should work to align with ECMA.

[Zorgatone]

It's just a warning/error from Typescript, but the generated code is correct and executes fine on runtime (first example only).

I know the second example will never work, it was a test

[RyanCavanaugh]

See #2361