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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_simple_queue
#include <boost/contract.hpp>
#include <boost/optional.hpp>
#include <vector>
#include <cassert>
template<typename T>
class simple_queue
#define BASES private boost::contract::constructor_precondition< \
simple_queue<T> >
: BASES
{
friend class boost::contract::access;
typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types;
#undef BASES
void invariant() const {
BOOST_CONTRACT_ASSERT(count() >= 0); // Non-negative count.
}
public:
/* Creation */
// Create empty queue.
explicit simple_queue(int a_capacity) :
boost::contract::constructor_precondition<simple_queue>([&] {
BOOST_CONTRACT_ASSERT(a_capacity > 0); // Positive capacity.
})
{
boost::contract::check c = boost::contract::constructor(this)
.postcondition([&] {
// Capacity set.
BOOST_CONTRACT_ASSERT(capacity() == a_capacity);
BOOST_CONTRACT_ASSERT(is_empty()); // Empty.
})
;
items_.reserve(a_capacity);
}
// Destroy queue.
virtual ~simple_queue() {
// Check invariants.
boost::contract::check c = boost::contract::destructor(this);
}
/* Basic Queries */
// Items in queue (in their order).
// (Somewhat exposes implementation but allows to check more contracts.)
std::vector<T> const& items() const {
// Check invariants.
boost::contract::check c = boost::contract::public_function(this);
return items_;
}
// Max number of items queue can hold.
int capacity() const {
// Check invariants.
boost::contract::check c = boost::contract::public_function(this);
return items_.capacity();
}
/* Derived Queries */
// Number of items.
int count() const {
int result;
boost::contract::check c = boost::contract::public_function(this)
.postcondition([&] {
// Return items count.
BOOST_CONTRACT_ASSERT(result == int(items().size()));
})
;
return result = items_.size();
}
// Item at head.
T const& head() const {
boost::optional<T const&> result;
boost::contract::check c = boost::contract::public_function(this)
.precondition([&] {
BOOST_CONTRACT_ASSERT(!is_empty()); // Not empty.
})
.postcondition([&] {
// Return item on top.
BOOST_CONTRACT_ASSERT(*result == items().at(0));
})
;
return *(result = items_.at(0));
}
// If queue contains no item.
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 = (items_.size() == 0);
}
// If queue has no room for another item.
bool is_full() const {
bool result;
boost::contract::check c = boost::contract::public_function(this)
.postcondition([&] {
BOOST_CONTRACT_ASSERT( // Consistent with size and capacity.
result == (capacity() == int(items().size())));
})
;
return result = (items_.size() == items_.capacity());
}
/* Commands */
// Remove head itme and shift all other items.
void remove() {
// Expensive all_equal postcond. and old_items copy might be skipped.
boost::contract::old_ptr<std::vector<T> > old_items;
#ifdef BOOST_CONTRACT_AUDIITS
= BOOST_CONTRACT_OLDOF(items())
#endif // Else, leave old pointer null...
;
boost::contract::old_ptr<int> old_count = BOOST_CONTRACT_OLDOF(count());
boost::contract::check c = boost::contract::public_function(this)
.precondition([&] {
BOOST_CONTRACT_ASSERT(!is_empty()); // Not empty.
})
.postcondition([&] {
BOOST_CONTRACT_ASSERT(count() == *old_count - 1); // Count dec.
// ...following skipped #ifndef AUDITS.
if(old_items) all_equal(items(), *old_items, /* shifted = */ 1);
})
;
items_.erase(items_.begin());
}
// Add item to tail.
void put(T const& item) {
// Expensive all_equal postcond. and old_items copy might be skipped.
boost::contract::old_ptr<std::vector<T> > old_items;
#ifdef BOOST_CONTRACT_AUDITS
= BOOST_CONTRACT_OLDOF(items())
#endif // Else, leave old pointer null...
;
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() < capacity()); // Room for add.
})
.postcondition([&] {
BOOST_CONTRACT_ASSERT(count() == *old_count + 1); // Count inc.
// Second to last item.
BOOST_CONTRACT_ASSERT(items().at(count() - 1) == item);
// ...following skipped #ifndef AUDITS.
if(old_items) all_equal(items(), *old_items);
})
;
items_.push_back(item);
}
private:
// Contract helper.
static bool all_equal(std::vector<T> const& left,
std::vector<T> const& right, unsigned offset = 0) {
boost::contract::check c = boost::contract::function()
.precondition([&] {
// Correct offset.
BOOST_CONTRACT_ASSERT(right.size() == left.size() + offset);
})
;
for(unsigned i = offset; i < right.size(); ++i) {
if(left.at(i - offset) != right.at(i)) return false;
}
return true;
}
std::vector<T> items_;
};
int main() {
simple_queue<int> q(10);
q.put(123);
q.put(456);
assert(q.capacity() == 10);
assert(q.head() == 123);
assert(!q.is_empty());
assert(!q.is_full());
std::vector<int> const& items = q.items();
assert(items.at(0) == 123);
assert(items.at(1) == 456);
q.remove();
assert(q.count() == 1);
return 0;
}
//]
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