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copied!<p>Here is a reference implementation (from <a href="https://en.wikipedia.org/w/index.php?title=Observer_pattern&oldid=342672104" rel="nofollow noreferrer">Wikipedia</a>).</p> <pre><code>#include <iostream> #include <string> #include <map> #include <boost/foreach.hpp> class SupervisedString; class IObserver{ public: virtual void handleEvent(const SupervisedString&) = 0; }; class SupervisedString{ // Observable class std::string _str; std::map<IObserver* const, IObserver* const> _observers; typedef std::map<IObserver* const, IObserver* const>::value_type item; void _Notify(){ BOOST_FOREACH(item iter, _observers){ iter.second->handleEvent(*this); } } public: void add(IObserver& ref){ _observers.insert(item(&ref, &ref)); } void remove(IObserver& ref){ _observers.erase(&ref); } const std::string& get() const{ return _str; } void reset(std::string str){ _str = str; _Notify(); } }; class Reflector: public IObserver{ // Prints the observed string into std::cout public: virtual void handleEvent(const SupervisedString& ref){ std::cout<<ref.get()<<std::endl; } }; class Counter: public IObserver{ // Prints the length of observed string into std::cout virtual void handleEvent(const SupervisedString& ref){ std::cout<<"length = "<<ref.get().length()<<std::endl; } }; int main(){ SupervisedString str; Reflector refl; Counter cnt; str.add(refl); str.reset("Hello, World!"); std::cout<<std::endl; str.remove(refl); str.add (cnt); str.reset("World, Hello!"); std::cout<<std::endl; return 0; } </code></pre>

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