Observer
12345678910111213141516171819202122232425262728293031323334 | #include <vector>
#include <functional>
class observer
{
public:
virtual void notify() = 0;
};
class observer_concrete : public observer
{
public:
virtual void notify() override
{ }
};
class subject
{
public:
void register_observer(observer& o)
{
observers.push_back(o);
}
void notify_observers()
{
for (observer& o : observers) {
o.notify();
}
}
private:
std::vector<std::reference_wrapper<observer>> observers;
}; |
This pattern is licensed under the CC0 Public Domain Dedication.
Intent
Notify generic observer objects when an event occurs.
Description
The observer pattern allows generic observer objects to be registered with a subject object and receive notifications when certain events occur.
The subject class, defined on lines 17–34, contains a
std::vector of references to observers line 33.
Observers (also known as listeners), in this case, are objects that
implement the observer interface (lines 4–8). The
register_observer function (lines 20–23) adds observers
to this std::vector, which are later to be notified by the
notify_observers function (lines 25–30).
We use std::reference_wrapper
for the elements of the std::vector (line 33), because the standard
containers require the element type to be assignable, which normal
reference types are not.
