php - PHP 中的单例引用和递归

Question

我有一个主 Bootstrap 类(下面示例中的 singleton1)，它实例化了一些单例类。在那些单例类中，我需要保留对应用程序主类的引用以便于快速引用它，但这样做给了我一个:

Fatal error: Maximum function nesting level of '100' reached, aborting

这是示例代码:

<?php

class Singleton1 {

    private static $instance;


    private function __construct() {

        Singleton2::instance();

    }

    public static function instance () {

        if( !self::$instance ) {
            $class = __CLASS__;
            self::$instance = new $class;
        }

        return self::$instance;
    }

    public function test () {
        echo 'Good.';
    }

    private function __clone() { }

    private function __wakeup() { }

}

class Singleton2 {

    private static $instance;

    private $singleton1;

    private function __construct() {
        $this->singleton1 = Singleton1::instance();
    }

    public static function instance () {

        if( !self::$instance ) {
            $class = __CLASS__;
            self::$instance = new $class;
        }

        return self::$instance;
    }

    public function test () {
        $this->singleton1->test();
    }

    private function __clone() { }

    private function __wakeup() { }

}

Singleton1::instance();

Singleton2::instance()->test();

我找不到对这个问题的任何合乎逻辑的解释......

谢谢。

Answer 1

您的代码有以下循环:

Singleton2::__construct()
Singleton1::instance()
Singleton1::__construct()
Singleton2::instance()
Singleton2::__construct()