42 lines
1.1 KiB
C++
42 lines
1.1 KiB
C++
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// Copyright (C) 2008-2018 Lorenzo Caminiti
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// Distributed under the Boost Software License, Version 1.0 (see accompanying
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// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
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// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
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#include <boost/contract.hpp>
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#include <boost/optional.hpp>
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#include <vector>
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#include <cassert>
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//[optional_result
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template<unsigned Index, typename T>
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T& get(std::vector<T>& vect) {
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boost::optional<T&> result; // Result not initialized here...
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boost::contract::check c = boost::contract::function()
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.precondition([&] {
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BOOST_CONTRACT_ASSERT(Index < vect.size());
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})
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.postcondition([&] {
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BOOST_CONTRACT_ASSERT(*result == vect[Index]);
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})
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;
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// Function body (executed after preconditions checked).
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return *(result = vect[Index]); // ...result initialized here instead.
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}
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//]
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int main() {
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std::vector<int> v;
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v.push_back(123);
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v.push_back(456);
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v.push_back(789);
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int& x = get<1>(v);
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assert(x == 456);
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x = -456;
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assert(v[1] == -456);
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return 0;
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}
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