refmgmt

Overview ¶

Package refmgmt provides a simple wrapper, which can be used to map a closable object type into an interface supporting reference counting and supporting a Dup() method.

The caller must provide an appropriate interface with the base object methods and additionally the Dup() (O, error) interface. Additionally, a struct type must be implemented hosting a View object (which implements the View.Close() and View.Dup() method) and the base object. It must implement the other interface methods by forwarding them to the base object. To create such a view object an appropriate creator function has to be provided.

The following example illustrates the usage:

 // Objectbase is the base interface for the
 // object type to be wrapped.
 type ObjectBase interface {
 	io.Closer

 	Value() (string, error)
 }

 ////////////////////////////////////////////////////////////////////////////////

 // Object is the final user facing interface.
 // It includes the base interface plus the Dup method.
 type Object interface {
 	ObjectBase
		Dup() (Object, error)
 }

 ////////////////////////////////////////////////////////////////////////////////

 // object is the implementation type for the bse object.
 type object struct {
 	lock   sync.Mutex
		closed bool
 	value  string
 }

 func (o *object) Value() (string, error) {
		if o.closed {
 		return "", fmt.Errorf("should not happen")
		}
 	return o.value, nil
 }

 func (o *object) Close() error {
		o.lock.Lock()
		defer o.lock.Unlock()

		if o.closed {
	 		return refmgmt.ErrClosed
		}
		o.closed = true
		return nil
 }

 ////////////////////////////////////////////////////////////////////////////////

 // view is the view object used to wrap the base object.
 // It forwards all methods to the base object using the
 // Execute function of the manager, to assure execution
 // on non-closed views, only.
 type view struct {
		*refmgmt.View[Object]
		obj ObjectBase
 }

 func (v *view) Value() (string, error) {
		value := ""

		err := v.Execute(func() (err error) {
	 		value, err = v.obj.Value() // forward to viewd object
	 		return
		})
		return value, err
 }

 // creator is the view object creator based on
 // the base object and the view manager.
 func creator(obj ObjectBase, v *refmgmt.View[Object]) Object {
 	return &view{v, obj}
 }