- property_exists: documentation ( source)
<?php
class A { public $b; };
$a = new A;
echo property_exists($a, 'b'); // Returns '1'
$a->b; // Remains silent
unset($a->b);
echo property_exists($a, 'b'); // Still returns '1'
$a->b; // Cause a "Notice: Undefined property A::$b"