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// Copyright (C) 2008-2018 Lorenzo Caminiti
// Distributed under the Boost Software License, Version 1.0 (see accompanying
// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
//[mitchell02_observer_main
#include "observer/observer.hpp"
#include "observer/subject.hpp"
#include <boost/contract.hpp>
#include <cassert>
int test_state; // For testing only.
// Implement an actual subject.
class concrete_subject
#define BASES public subject
: BASES
{
friend class boost::contract::access;
typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types; // Subcontracting.
#undef BASES
public:
typedef int state; // Some state being observed.
concrete_subject() : state_() {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::constructor(this);
}
virtual ~concrete_subject() {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::destructor(this);
}
void set_state(state const& new_state) {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::public_function(this);
state_ = new_state;
assert(state_ == test_state);
notify(); // Notify all observers.
}
state get_state() const {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::public_function(this);
return state_;
}
private:
state state_;
};
// Implement an actual observer.
class concrete_observer
#define BASES public observer
: BASES
{
friend class boost::contract::access;
typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types; // Subcontracting.
#undef BASES
BOOST_CONTRACT_OVERRIDES(up_to_date_with_subject, update)
public:
// Create concrete observer.
explicit concrete_observer(concrete_subject const& subj) :
subject_(subj), observed_state_() {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::constructor(this);
}
virtual ~concrete_observer() {
// Could have omitted contracts here (nothing to check).
boost::contract::check c = boost::contract::destructor(this);
}
// Implement base virtual functions.
bool up_to_date_with_subject(boost::contract::virtual_* v = 0)
const /* override */ {
bool result;
boost::contract::check c = boost::contract::public_function<
override_up_to_date_with_subject
>(v, result, &concrete_observer::up_to_date_with_subject, this);
return result = true; // For simplicity, assume always up-to-date.
}
void update(boost::contract::virtual_* v = 0) /* override */ {
boost::contract::check c = boost::contract::public_function<
override_update>(v, &concrete_observer::update, this);
observed_state_ = subject_.get_state();
assert(observed_state_ == test_state);
}
private:
concrete_subject const& subject_;
concrete_subject::state observed_state_;
};
int main() {
concrete_subject subj;
concrete_observer ob(subj);
subj.attach(&ob);
subj.set_state(test_state = 123);
subj.set_state(test_state = 456);
return 0;
}
//]
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