在Typescript中，Object.prototype函数可以返回Sub类型实例吗？

Question

I want to write code like

class Place {
  next: Place;
  get to() : Place {
    return this;
  }
}
let places : Place[]= [];
..

places[0].to.next = new Place();

There are many similar classes, so I want define 'to' property to Object.prototype.

Object.defineProperty(Object.prototye,"to",{
  get: function() {
    return this;
  }
});

But compilation has failed because of Property 'next' does not exist on type 'Object'

Can I return subtype in Typescript with Object.prototype function or property?

Answer 1

Typescript can't model exactly the beahavior you want.

The closest I can think of is to use a method not a property. For methods we can define a this parameter and infer it's type and use it as the return type:

class Place extends Object{
  next: Place;
}
let places: Place[] = [];

interface Object{
  to<T>(this: T):T; 
}
Object.prototype.to = function () {
  return this;
};

places[0].to().next = new Place();

The simplest solution would be to actually use a base class for all such objects with the property typed as polymorphic this :

class Base {
  get to(): this { return this; }
}
class Place extends Base{
  next: Place;
}
let places: Place[] = [];
places[0].to.next = new Place();

Note: Polluting the global Object does not seem like a great idea but ultimately that is your call.

Answer 2

I found some solution.

TS have a return type "this";

class Entity {
  self() : this {
    return this;
  } 
}

class Place extends Entity {
  where(toGo:string) {
    ....
  }
}

and I can use place like

new Place().self().where("Canada");

method self is decleared at super class but it can return sub class type.

So, I can use place instance without type casting.