ceph/src/boost/libs/stl_interfaces/example/node_iterator.cpp

   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 #include <boost/stl_interfaces/iterator_interface.hpp>
   7
   8 #include <algorithm>
   9 #include <array>
  10 #include <iostream>
  11
  12 #include <cassert>
  13
  14
  15 //[ node_defn
  16 template<typename T>
  17 struct node
  18 {
  19     T value_;
  20     node * next_; // == nullptr in the tail node
  21 };
  22 //]
  23
  24 //[ node_iterator_class_head
  25 template<typename T>
  26 struct node_iterator
  27     : boost::stl_interfaces::
  28           iterator_interface<node_iterator<T>, std::forward_iterator_tag, T>
  29 //]
  30 {
  31     //[ node_iterator_ctors
  32     constexpr node_iterator() noexcept : it_(nullptr) {}
  33     constexpr node_iterator(node<T> * it) noexcept : it_(it) {}
  34     //]
  35
  36     //[ node_iterator_user_ops
  37     constexpr T & operator*() const noexcept { return it_->value_; }
  38     constexpr node_iterator & operator++() noexcept
  39     {
  40         it_ = it_->next_;
  41         return *this;
  42     }
  43     friend constexpr bool
  44     operator==(node_iterator lhs, node_iterator rhs) noexcept
  45     {
  46         return lhs.it_ == rhs.it_;
  47     }
  48     //]
  49
  50     //[ node_iterator_using_declaration
  51     using base_type = boost::stl_interfaces::
  52         iterator_interface<node_iterator<T>, std::forward_iterator_tag, T>;
  53     using base_type::operator++;
  54     //]
  55
  56 private:
  57     node<T> * it_;
  58 };
  59
  60 //[ node_iterator_concept_check Equivalent to
  61 // static_assert(std::forward_iterator<node_iterator>, ""), or nothing in
  62 // C++17 and earlier.
  63 BOOST_STL_INTERFACES_STATIC_ASSERT_CONCEPT(node_iterator, std::forward_iterator)
  64 //]
  65
  66
  67 int main()
  68 {
  69     std::array<node<int>, 5> nodes;
  70     std::generate(nodes.begin(), nodes.end(), [] {
  71         static int i = 0;
  72         return node<int>{i++};
  73     });
  74     std::adjacent_find(
  75         nodes.begin(), nodes.end(), [](node<int> & a, node<int> & b) {
  76             a.next_ = &b;
  77             return false;
  78         });
  79     nodes.back().next_ = nullptr;
  80
  81     //[ node_iterator_usage
  82     node_iterator<int> const first(&nodes[0]);
  83     node_iterator<int> const last;
  84     for (auto it = first; it != last; it++) {
  85         std::cout << *it << " "; // Prints 0 1 2 3 4
  86     }
  87     std::cout << "\n";
  88     //]
  89 }