ecmall中static变量的使用-model模型代码设计

function &m($model_name, $params = array(), $is_new = false)
{
    static $models = array();
    $model_hash = md5($model_name . var_export($params, true));
    if ($is_new || !isset($models[$model_hash]))
    {
        $model_file = ROOT_PATH . '/includes/models/' . $model_name . '.model.php';
        if (!is_file($model_file))
        {
            /* 不存在该文件，则无法获取模型 */
            return false;
        }
        include_once($model_file);
        $model_name = ucfirst($model_name) . 'Model';
        if ($is_new)
        {
            return new $model_name($params, db());
        }
        $models[$model_hash] = new $model_name($params, db());
    }
    print_r($models[$model_hash]);
    return $models[$model_hash];
}

/**
 * 获取一个业务模型
 *
 * @param string $model_name
 * @param array $params
 * @param bool $is_new
 * @return object
 */
function &bm($model_name, $params = array(), $is_new = false)
{
    static $models = array();
    $model_hash = md5($model_name . var_export($params, true));
    if ($is_new || !isset($models[$model_hash]))
    {
        $model_file = ROOT_PATH . '/includes/models/' . $model_name . '.model.php';
        if (!is_file($model_file))
        {
            /* 不存在该文件，则无法获取模型 */
            return false;
        }
        include_once($model_file);
        $model_name = ucfirst($model_name) . 'BModel';
        if ($is_new)
        {
            return new $model_name($params, db());
        }
        $models[$model_hash] = new $model_name($params, db());
    }

    return $models[$model_hash];
}

使用static变量，当程序退出这段代码的时候，$model并不消失。这样减少了对象建时内存的消耗，有点类似单例模式。

比如这一段代码：

class Model
{
	function  __construct()
	{
		echo 'construct'.'<br>';
	}
}

function &m($model_name, $params = array(), $is_new = false)
{
    static $models = array();
    $model_hash = md5($model_name . var_export($params, true));
    if ($is_new || !isset($models[$model_hash]))
    {
        $model_name = ucfirst($model_name) . 'Model';
        if ($is_new)
        {
            return new Model();
        }
        $models[$model_hash] =  new Model();
    }
    return $models[$model_hash];
}

$s = m('db', array('name'));
$s1 = m('db', array('name'));

只执行了一次新建过程。