1// Copyright (C) 2019 T. Zachary Laine
2//
3// Distributed under the Boost Software License, Version 1.0. (See
4// accompanying file LICENSE_1_0.txt or copy at
5// http://www.boost.org/LICENSE_1_0.txt)
6//[ back_insert_iterator
7#include <boost/stl_interfaces/iterator_interface.hpp>
8
9#include <algorithm>
10#include <vector>
11
12#include <cassert>
13
14
15// This is an output iterator that holds a reference to a container, and calls
16// push_back() on that container when it is written to, just like
17// std::back_insert_iterator. This is not a lot less code to write than the
18// implementation of std::back_insert_iterator, but it demonstrates that
19// iterator_interface is flexible enough to handle this odd kind of iterator.
20template<typename Container>
21struct back_insert_iterator : boost::stl_interfaces::iterator_interface<
22#if !BOOST_STL_INTERFACES_USE_DEDUCED_THIS
23 back_insert_iterator<Container>,
24#endif
25 std::output_iterator_tag,
26 typename Container::value_type,
27 back_insert_iterator<Container> &>
28{
29 // For concept requirements.
30 back_insert_iterator() : c_(nullptr) {}
31
32 // Construct from a container.
33 explicit back_insert_iterator(Container & c) : c_(std::addressof(c)) {}
34
35 // When writing to *this, copy v into the container via push_back().
36 back_insert_iterator & operator=(typename Container::value_type const & v)
37 {
38 c_->push_back(v);
39 return *this;
40 }
41 // When writing to *this, move v into the container via push_back().
42 back_insert_iterator & operator=(typename Container::value_type && v)
43 {
44 c_->push_back(std::move(v));
45 return *this;
46 }
47
48 // Dereferencing *this just returns a reference to *this, so that the
49 // expression *it = value uses the operator=() overloads above.
50 back_insert_iterator & operator*() { return *this; }
51 // There is no underlying sequence over which we are iterating, so there's
52 // nowhere to go in next(). Do nothing.
53 back_insert_iterator & operator++() { return *this; }
54
55 using base_type = boost::stl_interfaces::iterator_interface<
56#if !BOOST_STL_INTERFACES_USE_DEDUCED_THIS
57 back_insert_iterator<Container>,
58#endif
59 std::output_iterator_tag,
60 typename Container::value_type,
61 back_insert_iterator<Container> &>;
62 using base_type::operator++;
63
64private:
65 Container * c_;
66};
67
68// A convenience function that creates a back_insert_iterator<Container>.
69template<typename Container>
70back_insert_iterator<Container> back_inserter(Container & c)
71{
72 return back_insert_iterator<Container>(c);
73}
74
75
76int main()
77{
78 std::vector<int> ints = {{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}};
79 std::vector<int> ints_copy;
80 std::copy(first: ints.begin(), last: ints.end(), result: ::back_inserter(c&: ints_copy));
81 assert(ints_copy == ints);
82}
83//]
84

source code of boost/libs/stl_interfaces/example/back_insert_iterator.cpp