interface类型定义了一组方法，如果某个对象实现了某个接口的所有方法，则此对象就实现了此接口

        type Instance func() Interface
        var adapters = make(map[string]Instance)
        func Register(name string, adapter Instance) {
	        adapters[name] = adapter
        }
        func NewInstance(adapterName string) (adapter Instance, err error) {
        	adapter, ok := adapters[adapterName]
			if !ok {
					err = fmt.Errorf("instance: unknown adapter name %q (forgot to 			import?)", adapterName)
					return
			}
			return
        }

        type Interface interface {
	        List()
	        Add()
	        Del()
	        Save()
        }

        func init(){
        	Register("l1",NewL1)
        	Register("l2",NewL2)

        }
        
        func NewL1() Instance{
        	return new(L1)
        }
        type L1 struct{}
        func(l *L1)List(){}
        func(l *L1)Add(){}
        func(l *L1)Del(){}
        func(l *L1)Save(){}
        
        func NewL1() Instance{
        	return new(L1)
        }
        type L2 struct{}
        func(l *L2)List(){}
        func(l *L2)Add(){}
        func(l *L2)Del(){}
        func(l *L2)Save(){}