Bug #4707 ยป 0005-clean-up-and-add-documentation-to-Observrable.patch
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#
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# observer.rb implements the _Observer_ object-oriented design pattern. The
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# Implementation of the _Observer_ object-oriented design pattern. The
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# following documentation is copied, with modifications, from "Programming
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# Ruby", by Hunt and Thomas; http://www.rubycentral.com/book/lib_patterns.html.
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#
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# == About
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#
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# The Observer pattern, also known as Publish/Subscribe, provides a simple
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# See Observable for more info.
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# The Observer pattern (also known as publish/subscribe) provides a simple
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# mechanism for one object to inform a set of interested third-party objects
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# when its state changes.
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#
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# == Mechanism
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#
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# In the Ruby implementation, the notifying class mixes in the +Observable+
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# The notifying class mixes in the +Observable+
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# module, which provides the methods for managing the associated observer
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# objects.
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#
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# The observers must implement the +update+ method to receive notifications.
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# The observers must implement a method called +update+ to receive notifications.
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#
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# The observable object must:
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# * assert that it has +changed+
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# * call +notify_observers+
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# * assert that it has +#changed+
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# * call +#notify_observers+
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#
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# == Example
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# === Example
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#
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# The following example demonstrates this nicely. A +Ticker+, when run,
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# continually receives the stock +Price+ for its +@symbol+. A +Warner+ is a
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# continually receives the stock +Price+ for its <tt>@symbol</tt>. A +Warner+ is a
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# general observer of the price, and two warners are demonstrated, a +WarnLow+
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# and a +WarnHigh+, which print a warning if the price is below or above their
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# set limits, respectively.
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| ... | ... | |
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# Current price: 112
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# Current price: 79
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# --- Sun Jun 09 00:10:25 CDT 2002: Price below 80: 79
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#
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# Implements the Observable design pattern as a mixin so that other objects can
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# be notified of changes in state. See observer.rb for details and an example.
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#
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module Observable
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#
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# Add +observer+ as an observer on this object. +observer+ will now receive
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# notifications. The second optional argument specifies a method to notify
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# updates, of which default value is +update+.
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# Add +observer+ as an observer on this object. so that it will receive
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# notifications.
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#
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# +observer+:: the object that will be notified of changes.
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# +func+:: Symbol naming the method that will be called when this Observable has changes.
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# This method must return true for +observer.respond_to?+ and will
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# receive <tt>*arg</tt> when #notify_observers is called, where <tt>*arg</tt>
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# is the value passed to #notify_observers by this Observable
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def add_observer(observer, func=:update)
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@observer_peers = {} unless defined? @observer_peers
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unless observer.respond_to? func
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| ... | ... | |
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end
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#
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# Delete +observer+ as an observer on this object. It will no longer receive
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# Remove +observer+ as an observer on this object so that it will no longer receive
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# notifications.
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#
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# +observer+:: An observer of this Observable
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def delete_observer(observer)
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@observer_peers.delete observer if defined? @observer_peers
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end
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#
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# Delete all observers associated with this object.
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# Remove all observers associated with this object.
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#
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def delete_observers
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@observer_peers.clear if defined? @observer_peers
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| ... | ... | |
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# Set the changed state of this object. Notifications will be sent only if
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# the changed +state+ is +true+.
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#
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# +state+:: Boolean indicating the changed state of this Observable.
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#
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def changed(state=true)
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@observer_state = state
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end
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#
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# Query the changed state of this object.
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# Returns true if this object's state has been changed since the last
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# #notify_observers call.
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#
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def changed?
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if defined? @observer_state and @observer_state
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| ... | ... | |
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end
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#
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# If this object's changed state is +true+, invoke the update method in each
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# currently associated observer in turn, passing it the given arguments. The
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# changed state is then set to +false+.
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# Notify observers of a change in state *if* this object's changed state is +true+.
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# This will invoke the method named in #add_observer, pasing <tt>*arg</tt>.
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# The changed state is then set to +false+.
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#
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# <tt>*arg</tt>:: Any arguments to pass to the observers.
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def notify_observers(*arg)
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if defined? @observer_state and @observer_state
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if defined? @observer_peers
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@observer_peers.each { |k, v|
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k.send v, *arg
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}
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@observer_peers.each do |k, v|
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k.send v, *arg
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end
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end
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@observer_state = false
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end
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