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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
#include <boost/contract.hpp>
#include <boost/optional.hpp>
#include <vector>
#include <cassert>
//[optional_result
template<unsigned Index, typename T>
T& get(std::vector<T>& vect) {
boost::optional<T&> result; // Result not initialized here...
boost::contract::check c = boost::contract::function()
.precondition([&] {
BOOST_CONTRACT_ASSERT(Index < vect.size());
})
.postcondition([&] {
BOOST_CONTRACT_ASSERT(*result == vect[Index]);
})
;
// Function body (executed after preconditions checked).
return *(result = vect[Index]); // ...result initialized here instead.
}
//]
int main() {
std::vector<int> v;
v.push_back(123);
v.push_back(456);
v.push_back(789);
int& x = get<1>(v);
assert(x == 456);
x = -456;
assert(v[1] == -456);
return 0;
}
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