在 PHP 中获取一个类的所有实例 [英] Get all instances of a class in PHP

问题描述

我想获取某个类的对象的所有实例.

I would like to get all the instances of an object of a certain class.

例如:

class Foo {
}

$a = new Foo();
$b = new Foo();

$instances = get_instances_of_class('Foo');

$instances 应该是 array($a, $b) 或 array($b, $a) (顺序不很重要).

$instances should be either array($a, $b) or array($b, $a) (order does not matter).

一个加号是如果函数将返回具有所请求类的超类的实例，尽管这不是必需的.

A plus is if the function would return instances which have a superclass of the requested class, though this isn't necessary.

我能想到的一种方法是使用一个静态类成员变量，它包含一个实例数组.在类的构造函数和析构函数中，我会从数组中添加或删除 $this.如果我必须在许多类上这样做，这会相当麻烦且容易出错.

One method I can think of is using a static class member variable which holds an array of instances. In the class's constructor and destructor, I would add or remove $this from the array. This is rather troublesome and error-prone if I have to do it on many classes.

推荐答案

如果您从 TrackableObject 类派生所有对象，则可以设置该类来处理此类事情(请确保您调用 parent::__construct() 和 parent::__destruct() 在子类中重载它们时.

If you derive all your objects from a TrackableObject class, this class could be set up to handle such things (just be sure you call parent::__construct() and parent::__destruct() when overloading those in subclasses.

class TrackableObject
{
    protected static $_instances = array();

    public function __construct()
    {
        self::$_instances[] = $this;
    }

    public function __destruct()
    {
        unset(self::$_instances[array_search($this, self::$_instances, true)]);
    }

    /**
     * @param $includeSubclasses Optionally include subclasses in returned set
     * @returns array array of objects
     */
    public static function getInstances($includeSubclasses = false)
    {
        $return = array();
        foreach(self::$_instances as $instance) {
            if ($instance instanceof get_class($this)) {
                if ($includeSubclasses || (get_class($instance) === get_class($this)) {
                    $return[] = $instance;
                }
            }
        }
        return $return;
    }
}

这样做的主要问题是垃圾收集不会自动拾取任何对象(因为对它的引用仍然存在于 TrackableObject::$_instances 中)，所以 __destruct() 需要手动调用以销毁所述对象.(循环引用垃圾回收是在 PHP 5.3 中添加的，可能会提供额外的垃圾回收机会)

The major issue with this is that no object would be automatically picked up by garbage collection (as a reference to it still exists within TrackableObject::$_instances), so __destruct() would need to be called manually to destroy said object. (Circular Reference Garbage Collection was added in PHP 5.3 and may present additional garbage collection opportunities)

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