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