Weak References

Table of Contents

The WeakRef class

Introduction

The WeakRef class provides a gateway to objects without preventing the garbage collector from freeing those objects. It also provides a way to turn a weak reference into a strong one.

Class synopsis

WeakRef
class WeakRef {
/* Methods */
public Weakref::__construct ( object $object )
public bool Weakref::acquire ( void )
public object Weakref::get ( void )
public bool Weakref::release ( void )
public bool Weakref::valid ( void )
}

Examples

Example #1 WeakRef usage example

<?php
class MyClass {
    public function 
__destruct() {
        echo 
"Destroying object!\n";
    }
}

$o1 = new MyClass;

$r1 = new WeakRef($o1);

if (
$r1->valid()) {
    echo 
"Object still exists!\n";
    
var_dump($r1->get());
} else {
    echo 
"Object is dead!\n";
}

unset(
$o1);

if (
$r1->valid()) {
    echo 
"Object still exists!\n";
    
var_dump($r1->get());
} else {
    echo 
"Object is dead!\n";
}
?>

The above example will output:

Object still exists!
object(MyClass)#1 (0) {
}
Destroying object!
Object is dead!

The WeakMap class

Introduction

Class synopsis

WeakMap
class WeakMap implements Countable , ArrayAccess , Iterator {
/* Methods */
public __construct ( void )
public int count ( void )
public mixed current ( void )
public object key ( void )
public void next ( void )
public bool offsetExists ( object $object )
public mixed offsetGet ( object $object )
public void offsetSet ( object $object , mixed $value )
public void offsetUnset ( object $object )
public void rewind ( void )
public bool valid ( void )
}

Examples

Example #1 Weakmap usage example

<?php
$wm 
= new WeakMap();

$o = new StdClass;

class 
{
    public function 
__destruct() {
        echo 
"Dead!\n";
    }
}

$wm[$o] = new A;

var_dump(count($wm));
echo 
"Unsetting..\n";
unset(
$o);
echo 
"Done\n";
var_dump(count($wm));

The above example will output:

int(1)
Unsetting..
Dead!
Done
int(0)