Review PHP设计模式之——注册模式

注册模式：

class DbConnections{
    var $_store = array();
    public function isValid($key) {
        return isset($this->_store[$key]);
    }

    public function &get($key){
        if (isset($this->_store[$key])) 
            return $this->_store[$key];
    }

    public function set($key, & $obj) {
        $this->_store[$key] = & $obj;
    }

    public function &getInstance(){
        static $instance = array();
        if (!$instance)
            $instance[0] = & new DbConnections;
        return $instance[0];
    }
}

class MysqlConnection{
    public $name = false;
    public function __construct($db){
        $this->name = $db;
        echo $db, "\n";
    }

    public function append($str){
        $this->name .= " ".$str;
    }
}

//initial setup, somewhere near the start of your script
$dbc = & DbConnections::getInstance();
$dbc->set('server1', new MysqlConnection('db1'));
$dbc->set('server2', new MysqlConnection('db2'));
$dbc->set('server3', new MysqlConnection('db3'));


$dbc1 = $dbc->get('server1');
$dbc2 = $dbc->get('server2');
$dbc3 = $dbc->get('server3');

$dbc1->append("connection");

var_dump($dbc->get('server1'));
var_dump($dbc->get('server2'));
var_dump($dbc->get('server3'));