Return type for methods of descendant classes?

[spud]

I've created a simplified version of the code I'm running through PHPStan:

class Queryer {

	public $results;
	
	/**
	 * @return self
	 */
	public function get_record($q): self
	{
		$this->results = send_query($q);
		return $this;
	}

}

class UserQueryer extends Queryer {
	/**
	 * @return self
	 */
	public function get_record($q): self
	{
		$this->results = send_query($q);
		$this->somethingOverridden = 'whatever';
		return $this;
	}
}

Basically, I have a generic database-querying class with a method "get_record" that returns the object itself, so methods can be chained.

Then I have class-specific inheritors of the class, like "UserQueryer" which might override the get_record method, as above.

If I set the return type of UserQueryer::get_record to "self" I get something like:

Child process error (exit code 255): Fatal error: Declaration of UserQueryer::get_record($q): UserQueryer must be compatible with Queryer::get_record($q): Queryer in /classes/UserQueryer.php on line nnn

Since the "self" type declaration should indicate an instanceof the class, this should have been valid, no?

How could I type hint the UserQueryer method correctly in this situation?

[ondrejmirtes]

Hi, this isn't so much related to PHPStan as to PHP itself. Your code doesn't work on PHP 7.3 and lower: https://3v4l.org/IVs47

It's because on PHP 7.4 and later this RFC allowed this usecase: https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters