Polymorphic `this` and Generics

First, thank you team for polymorphic this. It is really handy!

I think I ran into a case though that I am finding challenging, when I need to return a this, but the generics might have changed. For example:

class A<T> {
    private items: T[] = [];
    map<U>(callback: (item: T, idx: number, a: this) => U): this {
        // boring implementation details
    });
}

Where I want to be able to change the generic type for the class with a function, but I will be contracting to return the "current" class, but I want to guard different generics. The following seems logical to me, but doesn't appear to be currently supported:

class A<T> {
    private items: T[] = [];
    map<U>(callback: (item: T, idx: number, a: this) => U): this<U> {
        // boring implementation details
    });
}

Where if no generics arguments are supplied, it is inferred to be the current ones, where as if they are supplied they are substituted.

L'issue décrit une interaction proposée entre this polymorphe et la substitution de types génériques, mais ne nomme aucun fichier d'implémentation, test ou point d'entrée. Commencez par localiser la gestion de this polymorphe et de l'instanciation générique dans le compilateur ; le travail sera considéré comme terminé lorsque le comportement demandé de this<U> sera pris en charge avec les règles d'inférence et de substitution indiquées, et couvert par des tests.