Subject - object with views

SYNOPSIS

       #include <InterViews/subject.h>

DESCRIPTION

       A  subject is an object that has one or more views that it
       wishes to notify when it  changes.   The  SubjectIteractor
       class  can  be  used if it is necessary to iterate through
       the views of a subject explicitly.

       Because subjects are shared,  Subject  is  a  subclass  of
       Resource.  To allow for the possibility of multiple inher-
       itance, in which case  only  a  single  copy  of  resource
       information  should  be  maintained, Resource is a virtual
       base class.

PUBLIC OPERATIONS

       enum UpdateHint {
           attaching, detaching, setting, changing
       }
              This type enumerates possible hints when a  subject
              is  notifying  a  view  that  it  has changed.  The
              attaching hint indicates that a view  has  attached
              to  the subject.  The detaching hint means that the
              subject is being deleted and the view  should  con-
              sider itself detached.  The setting hint means that
              the subject's value has been set,  though  possibly
              to  the same value as it already has.  The changing
              hint means that the value is set to something  dif-
              ferent than it was previously.

       virtual void attach(View*)
              Add a view to the subject's list.

       virtual void detach(View*)
              Remove a view from the subject's list.

       virtual void notify(UpdateHint = changing)
              Notify  all the views of a subject that it has been
              updated.

       virtual boolean viewed_by(View*)
              Return whether a given view  is  on  the  subject's
              list of views.

       virtual void Attach(Interactor*)
              This  function  is equivalent to attach and is pro-
              vided solely for backward compatibility.   It  will
              be removed in a future version.

       virtual void Detach(Interactor*)
              will be removed in a future version.

       virtual void Notify()
              This function is equivalent to notify(changing) and
              is provided solely for backward compatibility.   It
              will be removed in a future version.

       boolean IsView(Interactor*)
              This  function  is  equivalent  to viewed_by and is
              provided solely  for  backward  compatibility.   It
              will be removed in a future version.

SUBJECTITERATOR OPERATIONS

       A  subject  iterator  can  be  used to iterate through the
       views in a subject.

       SubjectIterator(Subject*)
              Create a subject iterator for  the  given  subject.
              The  iterator  is only valid as long as the subject
              exists.

       virtual void init()
              Reset the iteration to start at  the  beginning  of
              the  list.   This  operation  is called by the con-
              structor.

       virtual boolean more()
              Return whether there are more views in the list.

       virtual View* cur()
              Return the current view.

       virtual void remove()
              Remove the current view from the list.

       virtual void next()
              Move the iteration to the next view in the list.

SEE ALSO

       View(3I)