The WeakMap class

(PHP 8)

简介

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.

类摘要

final WeakMap implements Countable , ArrayAccess , IteratorAggregate {
/* 方法 */
public __construct ( )
public count ( ) : int
abstract public getIterator ( ) : Traversable
public offsetExists ( object $object ) : bool
public offsetGet ( object $object ) : mixed
public offsetSet ( object $object , mixed $value ) : void
public offsetUnset ( object $object ) : void
}

范例

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));

以上例程会输出：

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

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