Typescript abstract child inheritance typing problematic

Question

How could I have "this.foo" as "Foo" in "Bar" class ?

abstract class AFoo {}

abstract class ABar {
    constructor(protected foo: AFoo) {}
}

class Foo extends AFoo {
    echoTest() {
        return 'test';
    };
}

class Bar extends ABar {
    constructor(foo: Foo) {
        super(foo)
    }

    write() {
        //Actually this line don't work cause this.foo is of AFoo type
        return this.foo.echoTest();
        //I want to avoid casting like this 
        //(<Foo>this.foo).echoTest();
    }
}

Expected the overloading of the constructor to induce the child type to the class