Open Mash Cross Reference
mash/tcl/common/observe.tcl

   # observe.tcl --
   #
   #       This file implements the Observer pattern.  An Observable
   #       object can attach one or more Observer objects to itself.
   #       This provide a convinient and extensible way of calling 
   #       a given method on a set of objects of different classes.  
   #
   # Copyright (c) 1997-2002 The Regents of the University of California.
   # All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions are met:
  #
  # A. Redistributions of source code must retain the above copyright notice,
  #    this list of conditions and the following disclaimer.
  # B. Redistributions in binary form must reproduce the above copyright notice,
  #    this list of conditions and the following disclaimer in the documentation
  #    and/or other materials provided with the distribution.
  # C. Neither the names of the copyright holders nor the names of its
  #    contributors may be used to endorse or promote products derived from this
  #    software without specific prior written permission.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS''
  # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  # ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR
  # ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  # SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  #
  # @(#) $Header: /usr/mash/src/repository/mash/mash-1/tcl/common/observe.tcl,v 1.8 2002/02/03 04:25:43 lim Exp $
  
  
  import mashutils
  
  Class Observer
  
  Observer instproc init { args } {
          eval [list $self] next $args
  }
  
  Observer instproc update { method args } {
          if [$self has_method $method] {
                  eval [list $self] [list $method] $args
          }
  }
  
  Class Observable
  
  Observable instproc init { args } {
          eval [list $self] next $args
          $self set observers_ { }
  }
  
  Observable instproc attach_observer { observer } {
          $self instvar observers_
          lappend observers_ $observer
  }
  
  Observable instproc detach_observer { observer } {
          $self instvar observers_
          set idx [lsearch $observers_ $observer]
          if { $idx != -1 } {
                  set observers_ [lreplace $observers_ $idx $idx]
          }
  }
  
  Observable instproc notify_observers { method args } {
          $self instvar observers_
          if [info exists observers_] {
                  foreach observer $observers_ {
                          eval [list $observer] update [list $method] $args
                  }
          }
  }