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Diffstat (limited to 'ruby_1_8_5/lib/observer.rb')
| -rw-r--r-- | ruby_1_8_5/lib/observer.rb | 192 |
1 files changed, 0 insertions, 192 deletions
diff --git a/ruby_1_8_5/lib/observer.rb b/ruby_1_8_5/lib/observer.rb deleted file mode 100644 index 64c7d81351..0000000000 --- a/ruby_1_8_5/lib/observer.rb +++ /dev/null @@ -1,192 +0,0 @@ -# -# observer.rb implements 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. -# -# == About -# -# 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+ -# module, which provides the methods for managing the associated observer -# objects. -# -# The observers must implement the +update+ method 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 +@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. -# -# 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 - - -# -# 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 - # notifications. - # - def add_observer(observer) - @observer_peers = [] unless defined? @observer_peers - unless observer.respond_to? :update - raise NoMethodError, "observer needs to respond to `update'" - end - @observer_peers.push observer - end - - # - # Delete +observer+ as an observer on this object. It will no longer receive - # notifications. - # - def delete_observer(observer) - @observer_peers.delete observer if defined? @observer_peers - end - - # - # Delete 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+. - # - def changed(state=true) - @observer_state = state - end - - # - # Query the changed state of this object. - # - 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+. - # - def notify_observers(*arg) - if defined? @observer_state and @observer_state - if defined? @observer_peers - for i in @observer_peers.dup - i.update(*arg) - end - end - @observer_state = false - end - end - -end |