observer.rb in rubysl-observer-2.0.0

- old
+ new

@@ -1,35 +1,36 @@
 #
-# observer.rb implements the _Observer_ object-oriented design pattern.  The
+# Implementation of the _Observer_ object-oriented design pattern.  The
 # following documentation is copied, with modifications, from "Programming
-# Ruby", by Hunt and Thomas; http://www.rubycentral.com/book/lib_patterns.html.
+# Ruby", by Hunt and Thomas; http://www.ruby-doc.org/docs/ProgrammingRuby/html/lib_patterns.html.
 #
-# == About
-#
-# The Observer pattern, also known as Publish/Subscribe, provides a simple
+# See Observable for more info.
+
+# The Observer pattern (also known as publish/subscribe) provides a simple
 # mechanism for one object to inform a set of interested third-party objects
 # when its state changes.
 #
 # == Mechanism
 #
-# In the Ruby implementation, the notifying class mixes in the +Observable+
+# The notifying class mixes in the +Observable+
 # module, which provides the methods for managing the associated observer
 # objects.
 #
-# The observers must implement the +update+ method to receive notifications.
+# The observers must implement a method called +update+ to receive
+# notifications.
 #
 # The observable object must:
-# * assert that it has +changed+
-# * call +notify_observers+
+# * assert that it has +#changed+
+# * call +#notify_observers+
 #
-# == Example
+# === Example
 #
 # The following example demonstrates this nicely.  A +Ticker+, when run,
-# continually receives the stock +Price+ for its +@symbol+.  A +Warner+ is a
-# general observer of the price, and two warners are demonstrated, a +WarnLow+
-# and a +WarnHigh+, which print a warning if the price is below or above their
-# set limits, respectively.
+# continually receives the stock +Price+ for its <tt>@symbol</tt>.  A +Warner+
+# is a general observer of the price, and two warners are demonstrated, a
+# +WarnLow+ and a +WarnHigh+, which print a warning if the price is below or
+# above their set limits, respectively.
 #
 # The +update+ callback allows the warners to run without being explicitly
 # called.  The system is set up with the +Ticker+ and several observers, and the
 # observers do their duty without the top-level code having to interfere.
 #
@@ -106,40 +107,43 @@
 #   +++ Sun Jun 09 00:10:25 CDT 2002: Price above 120: 134
 #   Current price: 134
 #   Current price: 112
 #   Current price: 79
 #   --- Sun Jun 09 00:10:25 CDT 2002: Price below 80: 79
-
-
-#
-# Implements the Observable design pattern as a mixin so that other objects can
-# be notified of changes in state.  See observer.rb for details and an example.
-#
 module Observable
 
   #
-  # Add +observer+ as an observer on this object. +observer+ will now receive
+  # Add +observer+ as an observer on this object. so that it will receive
   # notifications.
   #
-  def add_observer(observer)
-    @observer_peers = [] unless defined? @observer_peers
-    unless observer.respond_to? :update
-      raise NoMethodError, "observer needs to respond to `update'"
+  # +observer+:: the object that will be notified of changes.
+  # +func+:: Symbol naming the method that will be called when this Observable
+  #          has changes.
+  #
+  #          This method must return true for +observer.respond_to?+ and will
+  #          receive <tt>*arg</tt> when #notify_observers is called, where
+  #          <tt>*arg</tt> is the value passed to #notify_observers by this
+  #          Observable
+  def add_observer(observer, func=:update)
+    @observer_peers = {} unless defined? @observer_peers
+    unless observer.respond_to? func
+      raise NoMethodError, "observer does not respond to `#{func.to_s}'"
     end
-    @observer_peers.push observer
+    @observer_peers[observer] = func
   end
 
   #
-  # Delete +observer+ as an observer on this object. It will no longer receive
-  # notifications.
+  # Remove +observer+ as an observer on this object so that it will no longer
+  # receive notifications.
   #
+  # +observer+:: An observer of this Observable
   def delete_observer(observer)
     @observer_peers.delete observer if defined? @observer_peers
   end
 
   #
-  # Delete all observers associated with this object.
+  # Remove all observers associated with this object.
   #
   def delete_observers
     @observer_peers.clear if defined? @observer_peers
   end
 
@@ -156,34 +160,40 @@
 
   #
   # Set the changed state of this object.  Notifications will be sent only if
   # the changed +state+ is +true+.
   #
+  # +state+:: Boolean indicating the changed state of this Observable.
+  #
   def changed(state=true)
     @observer_state = state
   end
 
   #
-  # Query the changed state of this object.
+  # Returns true if this object's state has been changed since the last
+  # #notify_observers call.
   #
   def changed?
     if defined? @observer_state and @observer_state
       true
     else
       false
     end
   end
 
   #
-  # If this object's changed state is +true+, invoke the update method in each
-  # currently associated observer in turn, passing it the given arguments. The
-  # changed state is then set to +false+.
+  # Notify observers of a change in state *if* this object's changed state is
+  # +true+.
   #
+  # This will invoke the method named in #add_observer, passing <tt>*arg</tt>.
+  # The changed state is then set to +false+.
+  #
+  # <tt>*arg</tt>:: Any arguments to pass to the observers.
   def notify_observers(*arg)
     if defined? @observer_state and @observer_state
       if defined? @observer_peers
-        @observer_peers.dup.each do |i|
-          i.update(*arg)
+        @observer_peers.each do |k, v|
+          k.send v, *arg
         end
       end
       @observer_state = false
     end
   end