The WeakMap class

(PHP 8)

Introdução

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.

Sinopse da classe

final class WeakMap implements ArrayAccess, Countable, IteratorAggregate {

/* Métodos */

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

}

Exemplos

Exemplo #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));

O exemplo acima produzirá:

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

Índice

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

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User Contributed Notes 2 notes

down

mrblc at example dot com ¶

1 month 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.

down

-7

malferov at gmail dot com ¶

3 months 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

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