Cannot use final methods inside a constructor

[simonwelsh]

The check for which methods can be called before a class has been fully initialised is limited to private methods. I feel like this should be extended to include final methods, as those also can't be overridden in child classes. This is especially true for methods that are final because the class is final.

For example, I would expect this file to report No errors:

<?hh // strict

class A {
    public string $foo;

    public function __construct() { $this->setFoo('Hello'); }

    final public function setFoo(string $foo): void { $this->foo = $foo; }
}

final class B {
    public string $foo;

    public function __construct() { $this->setFoo('Hello'); }

    public function setFoo(string $foo): void { $this->foo = $foo; }
}

Whereas, it gives these errors

File "/home/vagrant/foo.php", line 14, characters 18-28:
Class B does not initialize all of its members; foo is not always initialized.
Make sure you systematically set $this->foo when the method __construct is called.
Alternatively, you can define the member as optional (?...)
 (NastCheck[3015])

File "/home/vagrant/foo.php", line 14, characters 34-46:
Until the initialization of $this is over, you can only call private methods
The initialization is not over because $this->foo can still potentially be null (NastCheck[3004])

File "/home/vagrant/foo.php", line 6, characters 18-28:
Class A does not initialize all of its members; foo is not always initialized.
Make sure you systematically set $this->foo when the method __construct is called.
Alternatively, you can define the member as optional (?...)
 (NastCheck[3015])

File "/home/vagrant/foo.php", line 6, characters 34-46:
Until the initialization of $this is over, you can only call private methods
The initialization is not over because $this->foo can still potentially be null (NastCheck[3004])

[lexidor]

👍 Absolutely!
This should be legal Hack.

[dlreeves]

I don't believe this is safe in general. See the following example

class A {
    public string $foo;

    public function __construct() { $this->setFoo('Hello'); }

    final public function setFoo(string $foo): void {
      echo $this->foo; // Not set yet
      $this->foo = $foo;
    }
}

[simonwelsh]

Yes, but a final method can add to the flow of the __construct() method, exactly like a private method.

class A {
    public string $foo;

    public function __construct() { $this->setFoo('Hello'); }

    private function setFoo(string $foo): void {
      echo $this->foo; // Not set yet
      $this->foo = $foo;
    }
}

Typing[4083] Read access to $this->foo before initialization
   --> test.hack
  7 |       echo $this->foo; // Not set yet
    |                   ^^^

A final method should work like this as well.