挺难懂的

下面这段代码如何理解呢，最好在关节点上给与解释

 * 行为模型实例 * * @param string $model 模型名称 * @return obj 对象形式的返回结果 */function Logic($model = null, $base_path = null){    static $_cache = array();    $cache_key = $model.'.'.$base_path;    if (!is_null($model) && isset($_cache[$cache_key])) return $_cache[$cache_key];    $base_path = $base_path == null ? BASE_DATA_PATH : $base_path;    $file_name = $base_path.'/logic/'.$model.'.logic.php';    $class_name = $model.'Logic';    if (!file_exists($file_name)){        return $_cache[$cache_key] =  new Model($model);    }else{        require_once($file_name);        if (!class_exists($class_name)){            $error = 'Logic Error:  Class '.$class_name.' is not exists!';            throw_exception($error);        }else{            return $_cache[$cache_key] = new $class_name();        }    }}

回复讨论(解决方案)

function Logic($model = null, $base_path = null){	//定义静态变量    static $_cache = array();	//定义缓存key值    $cache_key = $model.'.'.$base_path;	//若是静态变量中有这个模型的实例就直接返回    if (!is_null($model) && isset($_cache[$cache_key])) return $_cache[$cache_key];	//组织类文件路径    $base_path = $base_path == null ? BASE_DATA_PATH : $base_path;    $file_name = $base_path.'/logic/'.$model.'.logic.php';    $class_name = $model.'Logic';	//类文件是否存在    if (!file_exists($file_name)){		//不存在就实例一个model        return $_cache[$cache_key] =  new Model($model);    }else{		//存在就引入        require_once($file_name);		//判断是否存在 该类        if (!class_exists($class_name)){			//不存在就抛出异常            $error = 'Logic Error:  Class '.$class_name.' is not exists!';            throw_exception($error);        }else{			//存在就实例化它，存入静态数组中并返回            return $_cache[$cache_key] = new $class_name();        }    }}