PHP工厂模式、单例模式与注册树模式实例详解

<?php
namespace IMooc;
class Factory
{
  static function createDatabase()
  {
    $db = new Database();
    return $db;
  }
}

$db = IMooc\Factory::createDatabase();

<?php
namespace IMooc;
class Database
{
  protected $db;
  private function __construct()
  {
  }
  // 获取数据库操作实例
  static function getInstance()
  {
    if(self::$db){
      return self::$db;
    }else{
      self::$db = new self();
      return self::$db;
    }
  }
}
// 无论调用多少次,只会创建一个实例
$db = IMooc\Database::getInstance();
$db = IMooc\Database::getInstance();
$db = IMooc\Database::getInstance();
$db = IMooc\Database::getInstance();

<?php
namespace IMooc;
class Register
{
  protected static $objects;
  static function set($alias, $object)
  {
    self::$objects[$alias] = $object;
  }
  static function get($name)
  {
    return self::$objects[$name];
  }
  static function _unset($alias)
  {
    unset(self::$objects[$alias]);
  }
}
$db = \IMooc\Register::get('db1');