The WeakMap class

(PHP 8)

Introduction

A WeakMap is a map (or dictionary) that accepts objects as keys. However, unlike the otherwise similar SplObjectStorage, an object in a key of a WeakMap does not contribute toward the object's reference count. That is, if at any point the only remaining reference to an object is the key of a WeakMap, the object will be garbage collected and removed from the WeakMap. Its primary use case is for building caches of data derived from an object that do not need to live longer than the object.

WeakMap implements ArrayAccess, Traversable (via IteratorAggregate), and Countable, so in most cases it can be used in the same fashion as an associative array.

Class synopsis

final class WeakMap implements ArrayAccess, Countable, IteratorAggregate {

/* Methods */

public function count(): int

public function getIterator(): Iterator

public function offsetExists(object $object): bool

public function offsetGet(object $object): mixed

public function offsetSet(object $object, mixed $value): void

public function offsetUnset(object $object): 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)

WeakMap::count — Counts the number of live entries in the map
WeakMap::getIterator — Retrieve an external iterator
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

The WeakMap class

Introduction

Class synopsis

Examples

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