Working around loss of support for type constraint being self

Question

This is something I\'ve been doing in older versions of TypeScript and I use this method in C#, but it doesn\'t work in the latest 1.0 version of TypeScript.

Here\'s

Answer 1

promise() : T { return this; } it is very weak assumption that can be easily broken, because downcasting defined in a base class just cannot work for any sub-class

For example in you case, if anyone defines class SuperChild extends Child {} then promise() of SuperChild is going to give you Child instead of SuperChild.

Besides that here is how you can make it work the way it used to:

class Base {
    public children : Array;

    constructor(
        private toSelf: () => T,
        private toBase: (something: T) => Base
    ) {
    }


    doAction() {
        this.toBase(this.children[0]).promise(); // used to work
    }

    promise() : T {
        return this.toSelf(); // 
    }
}

class Child extends Base {
    public myString: string;
}

function toThis() { return this; }

new Child(toThis, x => x).promise().myString; // used to work