80 lines
2.7 KiB
C++
80 lines
2.7 KiB
C++
// Copyright (C) 2019 T. Zachary Laine
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//[ back_insert_iterator
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#include <boost/stl_interfaces/iterator_interface.hpp>
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#include <algorithm>
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#include <vector>
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#include <cassert>
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// This is an output iterator that holds a reference to a container, and calls
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// push_back() on that container when it is written to, just like
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// std::back_insert_iterator. This is not a lot less code to write than the
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// implementation of std::back_insert_iterator, but it demonstrates that
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// iterator_interface is flexible enough to handle this odd kind of iterator.
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template<typename Container>
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struct back_insert_iterator : boost::stl_interfaces::iterator_interface<
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back_insert_iterator<Container>,
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std::output_iterator_tag,
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typename Container::value_type,
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back_insert_iterator<Container> &>
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{
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// For concept requirements.
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back_insert_iterator() : c_(nullptr) {}
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// Construct from a container.
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explicit back_insert_iterator(Container & c) : c_(std::addressof(c)) {}
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// When writing to *this, copy v into the container via push_back().
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back_insert_iterator & operator=(typename Container::value_type const & v)
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{
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c_->push_back(v);
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return *this;
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}
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// When writing to *this, move v into the container via push_back().
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back_insert_iterator & operator=(typename Container::value_type && v)
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{
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c_->push_back(std::move(v));
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return *this;
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}
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// Dereferencing *this just returns a reference to *this, so that the
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// expression *it = value uses the operator=() overloads above.
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back_insert_iterator & operator*() { return *this; }
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// There is no underlying sequence over which we are iterating, so there's
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// nowhere to go in next(). Do nothing.
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back_insert_iterator & operator++() { return *this; }
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using base_type = boost::stl_interfaces::iterator_interface<
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back_insert_iterator<Container>,
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std::output_iterator_tag,
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typename Container::value_type,
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back_insert_iterator<Container> &>;
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using base_type::operator++;
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private:
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Container * c_;
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};
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// A convenience function that creates a back_insert_iterator<Container>.
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template<typename Container>
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back_insert_iterator<Container> back_inserter(Container & c)
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{
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return back_insert_iterator<Container>(c);
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}
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int main()
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{
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std::vector<int> ints = {{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}};
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std::vector<int> ints_copy;
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std::copy(ints.begin(), ints.end(), ::back_inserter(ints_copy));
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assert(ints_copy == ints);
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}
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//]
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