Question

Just playing around and I found this.

Why the call by reference to $this->newAxis() does not throw an undefined property notice (xAxis property), while the var_dump() does?

public function newXAxis()
{
    // var_dump(isset($this->xAxis)); // false
    // var_dump($this->xAxis); // Throws the notice
    return $this->newAxis($this->xAxis); // Should throw the notice?!
}

protected function newAxis(&$current)
{
    // ...
}

Does it have something to do with the passing by reference, thus not accessing the property directly?

Answer 1

Yes, it happens because you pass it by reference. When you pass by value, an attempt is made to actually read the value of the variable – so a notice appears. When you pass by reference, the value does not need to be read.

When you do that, the variable/property is created if it does not exist yet.

From the manual:

If you assign, pass, or return an undefined variable by reference, it
will get created.

<?php
function foo(&$var) { }
foo($a); // $a is "created" and assigned to null