Hacklang tutorial - this type in extend class [closed]

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What is correct answer for hack tutorial exercice 16?
Link to tutorial: Hacklang tutorial

My modified code (not marked as solution):

<?hh
// The type 'this' always points to the most derived type
class MyBaseClass {
  protected int $count = 0;

  public function add1(): this {
    $this->count += 1;
    return $this;
  }
}

class MyDerivedClass extends MyBaseClass {
  public function print_count(): void { echo $this->count; }
}

function test(): void {
  $x = new MyDerivedClass();
  $x->add1()->print_count();
}

I replaced MyBaseClass by this but still not marked as correct (green text with Exercice number) .. what is correct answer?

Answer 1

I'm an engineer working on Hack. I'm pretty sure we have a bug in our completion detection logic for this exercise in the tutorial. Your code looks correct to me -- changing the return type to this is, as far as I can see, all you were supposed to do. I'll follow up and get this bug fixed. Sorry about that!