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    WeakMap 类

    (PHP 8)

    简介

    WeakMap 是将对象作为 key 来访问的 map（或者说字典）。然而，与其它类似 SplObjectStorage 不同，WeakMap 中的对象 key 不影响对象的引用计数。也就是说，如果在任何时候对其唯一的剩余引用是 WeakMap key，那么该对象将会被垃圾收集并从 WeakMap 移除。它的主要用法是从对象中编译数据派生缓存，这种场景下不需要存活得比对象更久。

    WeakMap 实现了 ArrayAccess、 Iterator、Countable， 因此大多数情况下，它能和关联数组一样使用。

    类摘要

    final class WeakMap implements ArrayAccess, Countable, IteratorAggregate {
    /* 方法 */
    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
    }

    示例

    示例 #1 Weakmap 用法示例

    <?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));

    以上示例会输出：

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

    目录

    ＋add a note

    User Contributed Notes 2 notes

    up
    10
    mrblc at example dot com
    7 months 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
    -13
    malferov at gmail dot com
    8 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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