Submit a Pull Request Report a Bug

    The WeakMap class

    (PHP 8)

    Introduction

    A WeakMap is map (or dictionary) that accepts objects as keys. However, unlike the otherwise similar SplObjectStorage, an object in a key of 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, Iterator, 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 count(): int
    public getIterator(): Iterator
    public offsetExists(object $object): bool
    public offsetGet(object $object): mixed
    public offsetSet(object $object, mixed $value): void
    public 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)

    Table of Contents

    ＋add a note

    User Contributed Notes 2 notes

    up
    7
    mrblc at example dot com
    1 year ago
    @ malferov at gmail dot com

    It works as intended. As soon as:
    <?php
    $wp    [new stdClass()] = 'value';
    ?>
    is executed, number of references is zero and garbage collector will remove it.
    up
    -11
    malferov at gmail dot com
    1 year ago
    <?php

    $wp     = new WeakMap();

    // It's not working.
    // Has no error but not adding dynamically specifying object to map;
    // garbage collector will not be able to clear unnamed value, as I suppose
    $wp[new stdClass()] = 'value';
    echo     $wp->count() . PHP_EOL; // 0

    // It's working, as expected
    $obj = new stdClass();
    $wp[$obj] = 'value';
    echo     $wp->count(); // 1
    ＋add a note
    To Top