PHP 디자인 패턴의 서비스 로케이터 패턴 예에 대한 자세한 설명

class ServiceLocator {

    /**
     * 服务实例索引
     */
    privite $_services = [];

    /**
     * 服务定义索引
     */
    private $_definitions = [];
    
    /**
     * 是否全局服务共享（单例模式）
     */
    private $_shared = [];
    
    public function has($id){
        return isset($this->_services[$id]) || isset($this->_definitions[$id]);
    }
    
    public function __get($id){
        if($this->has($this->id)){
            $this->get($id);
        }
        
        // another implement
    }
    
    public function get($id){
        if(isset($this->_services[$id]) && $this->_shared[$id]){
            return $this->_services[$id];
        }
        
        if (isset($this->_definitions[$id])) {
            // 实例化
            $definition = $this->_definitions[$id];
            $object = Creator::createObject($definition);//省略服务实例化实现
            if($this->_shared[$id]){
                $this->_services[$id] = $object
            }
            
            return $object;
        }
        
        throw new Exception("无法定位服务{$id}")
    }
        
    public function set($id,$definition,$share = false){
        if ($definition === null) {
            unset($this->_services[$id], $this->_definitions[$id]);
            return;
        }
        
        unset($this->_services[$id]);
        $this->_shared[$id] = $share;
        if (is_string($definition)) {
            return $this->_definitions[$id] = $definition;
        }
        if (is_object($definition) || is_callable($definition, true)) {
            return $this->_definitions[$id] = $definition;
        }
        
        if (is_array($definition)) {
            if (isset($definition['class'])) {
                return $this->_definitions[$id] = $definition;
            }
        }
        
        throw new Exception("服务添加失败");
    }
}