Weak References

Table of Contents

Introduction
Installing/Configuring
WeakRef — The WeakRef class
- Weakref::acquire — Acquires a strong reference on that object
- Weakref::__construct — Constructs a new weak reference
- Weakref::get — Returns the object pointed to by the weak reference
- Weakref::release — Releases a previously acquired reference
- Weakref::valid — Checks whether the object referenced still exists
WeakMap — The WeakMap class
- WeakMap::__construct — Constructs a new map
- WeakMap::count — Counts the number of live entries in the map
- WeakMap::current — Returns the current value under iteration
- WeakMap::key — Returns the current key under iteration.
- WeakMap::next — Advances to the next map element
- WeakMap::offsetExists — Checks whether a certain object is in the map
- WeakMap::offsetGet — Returns the value pointed to by a certain object
- WeakMap::offsetSet — Updates the map with a new key-value pair
- WeakMap::offsetUnset — Removes an entry from the map
- WeakMap::rewind — Rewinds the iterator to the beginning of the map
- WeakMap::valid — Returns whether the iterator is still on a valid map element

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 A {
    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)