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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 <string>
- #include <cassert>
- //[old
- char replace(std::string& s, unsigned index, char x) {
- char result;
- boost::contract::old_ptr<char> old_char; // Null, old value copied later...
- boost::contract::check c = boost::contract::function()
- .precondition([&] {
- BOOST_CONTRACT_ASSERT(index < s.size());
- })
- .old([&] { // ...after preconditions (and invariants) checked.
- old_char = BOOST_CONTRACT_OLDOF(s[index]);
- })
- .postcondition([&] {
- BOOST_CONTRACT_ASSERT(s[index] == x);
- BOOST_CONTRACT_ASSERT(result == *old_char);
- })
- ;
- result = s[index];
- s[index] = x;
- return result;
- }
- //]
- int main() {
- std::string s = "abc";
- char r = replace(s, 1, '_');
- assert(s == "a_c");
- assert(r == 'b');
- return 0;
- }
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