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Diffstat (limited to 'ruby_1_9_3/lib/observer.rb')
| -rw-r--r-- | ruby_1_9_3/lib/observer.rb | 202 |
1 files changed, 0 insertions, 202 deletions
diff --git a/ruby_1_9_3/lib/observer.rb b/ruby_1_9_3/lib/observer.rb deleted file mode 100644 index a5d0dc0f4e..0000000000 --- a/ruby_1_9_3/lib/observer.rb +++ /dev/null @@ -1,202 +0,0 @@ -# -# 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. -# -# 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 -# -# The notifying class mixes in the +Observable+ -# module, which provides the methods for managing the associated observer -# objects. -# -# The observers must implement a method called +update+ to receive -# notifications. -# -# The observable object must: -# * assert that it has +#changed+ -# * call +#notify_observers+ -# -# === Example -# -# The following example demonstrates this nicely. A +Ticker+, when run, -# 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. -# -# Note that the contract between publisher and subscriber (observable and -# observer) is not declared or enforced. The +Ticker+ publishes a time and a -# price, and the warners receive that. But if you don't ensure that your -# contracts are correct, nothing else can warn you. -# -# require "observer" -# -# class Ticker ### Periodically fetch a stock price. -# include Observable -# -# def initialize(symbol) -# @symbol = symbol -# end -# -# def run -# lastPrice = nil -# loop do -# price = Price.fetch(@symbol) -# print "Current price: #{price}\n" -# if price != lastPrice -# changed # notify observers -# lastPrice = price -# notify_observers(Time.now, price) -# end -# sleep 1 -# end -# end -# end -# -# class Price ### A mock class to fetch a stock price (60 - 140). -# def Price.fetch(symbol) -# 60 + rand(80) -# end -# end -# -# class Warner ### An abstract observer of Ticker objects. -# def initialize(ticker, limit) -# @limit = limit -# ticker.add_observer(self) -# end -# end -# -# class WarnLow < Warner -# def update(time, price) # callback for observer -# if price < @limit -# print "--- #{time.to_s}: Price below #@limit: #{price}\n" -# end -# end -# end -# -# class WarnHigh < Warner -# def update(time, price) # callback for observer -# if price > @limit -# print "+++ #{time.to_s}: Price above #@limit: #{price}\n" -# end -# end -# end -# -# ticker = Ticker.new("MSFT") -# WarnLow.new(ticker, 80) -# WarnHigh.new(ticker, 120) -# ticker.run -# -# Produces: -# -# Current price: 83 -# Current price: 75 -# --- Sun Jun 09 00:10:25 CDT 2002: Price below 80: 75 -# Current price: 90 -# Current price: 134 -# +++ 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 -module Observable - - # - # Add +observer+ as an observer on this object. so that it will receive - # notifications. - # - # +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[observer] = func - end - - # - # 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 - - # - # Remove all observers associated with this object. - # - def delete_observers - @observer_peers.clear if defined? @observer_peers - end - - # - # Return the number of observers associated with this object. - # - def count_observers - if defined? @observer_peers - @observer_peers.size - else - 0 - end - end - - # - # 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 - - # - # 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 - - # - # Notify observers of a change in state *if* this object's changed state is - # +true+. - # - # This will invoke the method named in #add_observer, pasing <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.each do |k, v| - k.send v, *arg - end - end - @observer_state = false - end - end - -end |