thisType versus this

[electricessence]

#9063 (comment)

Wanted to open the discussion to possibly allowing for something other than this for polymorphic typing.

Right now...

class A<T> {
    clone():this {
       return <any> new A<T>();  // without <any> it complains.
    }
   me():this {
      return this; // doesn't complain
   }
}

And it would be really nice to be able to:

class A<T> {
    map<TResult>(mapper: (v: T) => TResult): this<TResult>{
       // ...
    }
}

[DanielRosenwasser]

But your clone method doesn't return something of type this, it returns something of type A<T>. If you extended A with a class named B, clone wouldn't give you something with the members that B has.

A simple way to look at it is that the this type is supposed to model the type of the expression that you're calling a method off of.

As for the second thing, I think that's a duplicate of #6223.

[kitsonk]

It is, and the biggest challenge discussed in there is that if the arity of the generic arguments changes, how is this handled.