test.ts

class A {
  get a() {
    return 1
  }
}
class B {
  get b() {
    return 2
  }
}

class Foo {
  constructor(private hey: boolean = true) { }

  get foo() {
    return this.hey ? new A() : new B();
  }
}

const foo = new Foo()

const loo = foo.foo