60 lines
1.6 KiB
C++
60 lines
1.6 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 <cassert>
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//[friend_invariant
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template<typename T>
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class positive {
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public:
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void invariant() const {
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BOOST_CONTRACT_ASSERT(value() > 0);
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}
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// Can be considered an extension of enclosing class' public interface...
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friend void swap(positive& object, T& value) {
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boost::contract::old_ptr<T> old_object_value =
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BOOST_CONTRACT_OLDOF(object.value());
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boost::contract::old_ptr<T> old_value = BOOST_CONTRACT_OLDOF(value);
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// ...so it can be made to check invariants via `public_function`.
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boost::contract::check c = boost::contract::public_function(&object)
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.precondition([&] {
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BOOST_CONTRACT_ASSERT(value > 0);
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})
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.postcondition([&] {
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BOOST_CONTRACT_ASSERT(object.value() == *old_value);
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BOOST_CONTRACT_ASSERT(value == *old_object_value);
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})
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;
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T saved = object.value_;
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object.value_ = value;
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value = saved;
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}
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private:
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T value_;
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/* ... */
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//]
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public:
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// Could program contracts for following too.
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explicit positive(T const& value) : value_(value) {}
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T value() const { return value_; }
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};
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int main() {
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positive<int> i(123);
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int x = 456;
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swap(i, x);
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assert(i.value() == 456);
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assert(x == 123);
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return 0;
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}
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