Greeter.ts

class Greeter implements Person {
    protected person: Person;

    constructor(person: Person) {
        this.person = person;
    }

    public greet(): string {
        return this.person.greet();
    }
}

class HiGreeter extends Greeter {
    public greet(): string {
        return 'Hi!';
    }
}

class GoodMorningGreeter extends Greeter {
    public greet(): string {
        return 'Good morning!';
    }
}