import "reflect-metadata";

class Point {
    x: number = 0;
    y: number = 0;
}

class Line {
    private _p0: Point = new Point();
    private _p1: Point = new Point();

    @validate
    set p0(value: Point) { this._p0 = value; }
    get p0() { return this._p0; }

    @validate
    set p1(value: Point) { this._p1 = value; }
    get p1() { return this._p1; }
}

function validate<T>(target: any, propertyKey: string, descriptor: TypedPropertyDescriptor<T>) {
    let set = descriptor.set || (x => { });
    descriptor.set = function (value: T) {
        let type = Reflect.getMetadata("design:type", target, propertyKey);
        if (!(value instanceof type)) {
            throw new TypeError("Invalid type.");
        }
        set(value); // <- no funciona
    }
}


let line = new Line();

// line.p0 = new Point();
// line.p1 = new Point();
// console.log(line.p0.x);
// console.log(line.p1.y);