Description of current accessors guarding

gistfile1.php

<?php

class a {
    public $Foo {
        get   { echo 'G '; return $this->Foo; }
        set   { echo 'S '; $this->Foo = $value; }
        isset { echo 'I '; return isset($this->Foo); }
        unset { echo 'U '; unset($this->Foo); }
    }  
}

$o = new a();
var_dump($o)
// object(a)#1 (1) {
//   ["Foo"]=>
//   NULL
// }

$o->Foo = 5;
// S      <-- Note the echo in each of the accessors for call "tracing"

echo (int)isset($o->Foo);
// I G 1  <-- Note the first I (call to accessor), then isset() calls the getter (to get the value), finally returning true

unset($o->Foo);
// U      <-- 2nd call to unset() does not call the unsetter (guarded) nor does it call the getter

var_dump($o)
// object(a)#1 (0) {
// }
// Note how the property is gone, it has been unset

$o->Foo = 5;
// S 

var_dump($o)
// object(a)#1 (1) {
//   ["Foo"]=>
//   int(5)
// }