Conflict betwen Partial and 'this' type

[WanderWang]

TypeScript Version: 2.1.4 / nightly (2.2.0-dev.20170102)

Code

class Tween<T>{

    static get<T>(target: T): Tween<T> {
        return new Tween(target);
    }

    constructor(private target: T) {
    }

    public to(props: Partial<T>) {
    }
}

class DisplayObject {
    public x: number;
    public y: number;
}


class Button extends DisplayObject {

    public z: number;
    onClick = () => {
        let tween = Tween.get(this);
        tween.to({ x: 100 });
        tween.to({ z: 100 });
        tween.to({ a: 100 });
    }
}

Expected behavior:

        let tween = Tween.get(this); 
        tween.to({ x: 100 }); // right 
        tween.to({ z: 100 }); // right 
        tween.to({ a: 100 }); // compile error

Actual behavior:

        let tween = Tween.get(this); 
        tween.to({ x: 100 }); // compile error 
        tween.to({ z: 100 }); // compile error 
        tween.to({ a: 100 }); // compile error

[dsehnal]

I have observed a possibly related issue in nightly (2.2.0-dev.20170103) with the code:

export abstract class A<P> { public props: P; }

export abstract class B<T, P extends { params: T }> extends A<P> {
    public get params(): this['props']['params'] { return this.props.params; }
    update(params: Partial<this['params']>) {
        // ...
    }
}

export interface P { x: number, y: string }
export class C extends B<P, { params: P }> {
    f() {
        const p = this.params;
        this.update({ x: p.x + 1 }); // compile error here
    }
}

[WanderWang]

Who can give me a feedback ?

@ahejlsberg @DanielRosenwasser

[ahejlsberg]

@WanderWang I'd suggest changing the to method to use Pick<T, K>:

    public to<K extends keyof T>(props: Pick<T, K>) {
    }

For more discussion on a similar issue, see #12793.

[WanderWang]

thanks @ahejlsberg , it works !!! I think I can close this issue and concern about #12793