PHP扩展类使子级继承相同的静态属性 [英] PHP Extending class makes children inherit same static property

问题描述

我想先展示一个测试用例:

I'd like to start by showing a test case:

class A {
    public static $instance=null;
    public function __construct(){
        self::$instance=$this;
    }
    public function className(){
        return get_class(self::$instance);
    }
}

class B extends A {
    public function className(){
        return get_class(self::$instance);
    }
}

// test code
$b=new B();
echo $b->className; // B
$a=new A();
echo $a->className; // A
echo $b->className; // A <- error: not B any more!

注释

• 我在上面使用的是factory + singleton模式.好吧.
• 我不需要任何有关正确实现模式"的规范.我需要解决问题，而不是违反KISS的;).
评论家可能会说A应该是接口.理想情况下，应该是这样，但是很简单，很抱歉.

• I'm using a factory+singleton patterns above. Well, somewhat.
• I don't need any specs on "implementing patterns correctly". I need problem solving, not KISS violations ;).
• Critics might say A should be an interface. Ideally, that's what it should have been, but it's just a simple class, sorry.

问题在于所有实例的self::$instance都相同.如何为每个班级分开self::$instance?

The issues lies in the fact that self::$instance is the same for all instances. How do I separate self::$instance for each class?

我有这个主意:

$GLOBALS['store']=array();
class A {
    public static $instance=null;
    public function __construct(){
        $GLOBALS['store'][__CLASS__]=$this;
    }
}

推荐答案

您可以按类名称存储实例:

You could store an instance per class name:

class A { 
    public static function getInstance(){
        // Maybe use this function to implement the singleton pattern ...
        return self::$instance[get_called_class()];
    }

    public function className(){
        return get_class(self::getInstance());
    }   
}

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