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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_stack
#include <boost/contract.hpp>
#include <boost/optional.hpp>
#include <vector>
#include <cassert>
template<typename T>
class stack {
friend class boost::contract::access;
void invariant() const {
BOOST_CONTRACT_ASSERT(count() >= 0); // Non-negative count.
}
public:
/* Creation */
// Create empty stack.
stack() {
boost::contract::check c = boost::contract::constructor(this)
.postcondition([&] {
BOOST_CONTRACT_ASSERT(count() == 0); // Empty.
})
;
}
// Destroy stack.
virtual ~stack() {
// Check invariants.
boost::contract::check c = boost::contract::destructor(this);
}
/* Basic Queries */
// Number of items.
int count() const {
// Check invariants.
boost::contract::check c = boost::contract::public_function(this);
return items_.size();
}
// Item at index in [1, count()] (as in Eiffel).
T const& item_at(int index) const {
boost::contract::check c = boost::contract::public_function(this)
.precondition([&] {
BOOST_CONTRACT_ASSERT(index > 0); // Positive index.
BOOST_CONTRACT_ASSERT(index <= count()); // Index within count.
})
;
return items_[index - 1];
}
/* Derived Queries */
// If no items.
bool is_empty() const {
bool result;
boost::contract::check c = boost::contract::public_function(this)
.postcondition([&] {
// Consistent with count.
BOOST_CONTRACT_ASSERT(result == (count() == 0));
})
;
return result = (count() == 0);
}
// Top item.
T const& item() const {
boost::optional<T const&> result; // Avoid extra construction of T.
boost::contract::check c = boost::contract::public_function(this)
.precondition([&] {
BOOST_CONTRACT_ASSERT(count() > 0); // Not empty.
})
.postcondition([&] {
// Item on top.
BOOST_CONTRACT_ASSERT(*result == item_at(count()));
})
;
return *(result = item_at(count()));
}
/* Commands */
// Push item to the top.
void put(T const& new_item) {
boost::contract::old_ptr<int> old_count = BOOST_CONTRACT_OLDOF(count());
boost::contract::check c = boost::contract::public_function(this)
.postcondition([&] {
BOOST_CONTRACT_ASSERT(count() == *old_count + 1); // Count inc.
BOOST_CONTRACT_ASSERT(item() == new_item); // Item set.
})
;
items_.push_back(new_item);
}
// Pop top item.
void remove() {
boost::contract::old_ptr<int> old_count = BOOST_CONTRACT_OLDOF(count());
boost::contract::check c = boost::contract::public_function(this)
.precondition([&] {
BOOST_CONTRACT_ASSERT(count() > 0); // Not empty.
})
.postcondition([&] {
BOOST_CONTRACT_ASSERT(count() == *old_count - 1); // Count dec.
})
;
items_.pop_back();
}
private:
std::vector<T> items_;
};
int main() {
stack<int> s;
assert(s.count() == 0);
s.put(123);
assert(s.item() == 123);
s.remove();
assert(s.is_empty());
return 0;
}
//]
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