Cannot return new derived object from interface function

Question

Typescript code does not compile.

Compiler output: error TS2416: Property 'deepcopy' in type 'Vector2' is not assignable to the same property in base type 'Vector'.

I just started using typescript yesterday and this seems like a trivial issue but cannot seem to find a proper solution to the problem.

interface Vector {
    deepcopy() : this;
}

export class Vector2 implements Vector {
    constructor() {
    }

    deepcopy() {
        return new Vector2();
    }
}

Any suggestions or clues?

Answer 1

interface Vector {
    deepcopy() : Vector;
}

export class Vector2 implements Vector {
    constructor() {
    }

    deepcopy() {
        return new Vector2();
    }
}

The problem with your code is that this is not a type. As a consequence Vector2 does not match it. By changing it to Vector you can return your instance implementing the Vector interface as you want.