Class SubjectSlot

source code

                   object --+    
                            |    
Disconnectable.Disconnectable --+
                                |
                               SubjectSlot

This class maintains the relationship between a subject and a
listener callback. As soon as both are non-null, it connects the
listener the given 'event' of the subject and release the connection
when any of them change.

The finalizer of the object also cleans up both parameters and so
does the __exit__ override, being able to use it as a context
manager with the 'with' clause.

Note that 'event' is a string with canonical identifier for the
listener, i.e., the subject should provide the methods:

  add_[event]_listener
  remove_[event]_listener
  [event]_has_listener

Note that the connection can already be made manually before the
subject and listener are fed to the slot.