PHP design pattern 2: factory mode, singleton mode, registration tree mode

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1. Factory Pattern: Generate objects in factory methods or classes instead of directly new in the code
Advantages: When a common class needs new in multiple places, use the factory pattern to facilitate the expansion and maintenance of the class
File directory: Frame/Factory.php

<?php
namespace Frame;
use Frame\Database;
use Frame\Register;

class Factory
{
    static function createDatabase()
    {
        //$db = new Database(); //正常实例化类
        $db = Database::getInstance();    //获取单例模式的类
        Register::set(&#39;db&#39;,$db);          //将实例化后的类注册到全局注册树中
        return $db;
    }
}
//外部调用得到$db对象
$db = Frame\Factory::createDatabase();
//获取全局注册树中的对象
$db = Frame\Register::get(&#39;db&#39;);
//卸载全局注册树中的对象
$db = Frame\Register::_unset(&#39;db&#39;);
?>

2. Singleton mode: Only new instantiation objects are allowed in the class itself
Advantages: The class cannot be new externally, and The object is created once in the class itself, saving resource overhead
File directory: Frame/Database.php

<?php
namespace Frame;

class Database
{
    protected $db;
    
    //单例模式，私有化__construct()方法，不允许外部实例化对象
    private function __construct()
    {
    }
    //实例化本类
    static function getInstance()
    {
        if(self::$db) {
            return self::$db;
        } else {
            self::$db = new self();
            return self::$db;
        }
    }
}
//外部调用
$db = Frame\Database::getInstance();
?>

3. Registration tree mode: Register an object into the global registration tree for convenience Global use
Storage directory: Frame/Register.php

<?php
namespace Frame;

class Register
{
    protected $objects;
    /*
    *    将实例化后的类注册到全局注册树中
    *    $alias :对象别名
    *    $object:实例化后的对象
    */
    static function set($alias,$object)
    {
        self::$objects[$alias] = $object;
    }
    /*
    *    卸载实例化后的类
    *    $alias :对象别名
    */
    static function _unset($alias)
    {
        unset(self::$objects[$alias]);
    }
    /*
    *    获取实例化后的类对象
    *    $alias : 对象别名
    */
    static function get($alias)
    {
        return self::$objects[$alias];
    }
    
}
?>

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