gistfile1.txt

<?php
class A {
	public function test() {
		$this->abc[] = 'test';
	}
}

class B extends A {
	public $abc = array('pre-test');
}

$a = new A();
print_r($a);

echo'<br>';
$a->test();
print_r($a);

echo'<br>';
$b = new B();
print_r($b);

echo'<br>';
$b->test();
print_r($b);
// output is 
// B Object ( [abc] => Array ( [0] => pre-test [1] => test ) )
// - property is populated properly