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 //[ interoperability
7 #include <boost/stl_interfaces/iterator_interface.hpp>
8
9 #include <algorithm>
10 #include <array>
11 #include <numeric>
12
13 #include <cassert>
14
15
16 // This is a random access iterator templated on a value type. The ValueType
17 // template parameter allows us easily to define const and non-const iterators
18 // from the same template.
19 template<typename ValueType>
20 struct random_access_iterator : boost::stl_interfaces::iterator_interface<
21 random_access_iterator<ValueType>,
22 std::random_access_iterator_tag,
23 ValueType>
24 {
25 static_assert(std::is_object<ValueType>::value, "");
26
27 // Default constructor.
random_access_iteratorrandom_access_iterator28 constexpr random_access_iterator() noexcept {}
29
30 // Construction from an underlying pointer.
random_access_iteratorrandom_access_iterator31 constexpr random_access_iterator(ValueType * it) noexcept : it_(it) {}
32
33 // Implicit conversion from an existing random_access_iterator with a
34 // possibly different value type. The enable_if logic here just enforces
35 // that this constructor only participates in overload resolution when the
36 // expression it_ = other.it_ is well-formed.
37 template<
38 typename ValueType2,
39 typename E = std::enable_if_t<
40 std::is_convertible<ValueType2 *, ValueType *>::value>>
random_access_iteratorrandom_access_iterator41 constexpr random_access_iterator(
42 random_access_iterator<ValueType2> other) noexcept :
43 it_(other.it_)
44 {}
45
operator *random_access_iterator46 constexpr ValueType & operator*() const noexcept { return *it_; }
operator +=random_access_iterator47 constexpr random_access_iterator & operator+=(std::ptrdiff_t i) noexcept
48 {
49 it_ += i;
50 return *this;
51 }
operator -random_access_iterator52 constexpr auto operator-(random_access_iterator other) const noexcept
53 {
54 return it_ - other.it_;
55 }
56
57 private:
58 ValueType * it_;
59
60 // This friendship is necessary to enable the implicit conversion
61 // constructor above to work.
62 template<typename ValueType2>
63 friend struct random_access_iterator;
64 };
65
66 using iterator = random_access_iterator<int>;
67 using const_iterator = random_access_iterator<int const>;
68
main()69 int main()
70 {
71 std::array<int, 10> ints = {{0, 2, 1, 3, 4, 5, 7, 6, 8, 9}};
72
73 // Create and use two mutable iterators.
74 iterator first(ints.data());
75 iterator last(ints.data() + ints.size());
76 std::sort(first, last);
77 assert(ints == (std::array<int, 10>{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}}));
78
79 // Create and use two constant iterators, one from an existing mutable
80 // iterator.
81 std::array<int, 10> int_sums;
82 const_iterator cfirst(ints.data());
83 const_iterator clast = last;
84 std::partial_sum(cfirst, clast, int_sums.begin());
85 assert(int_sums == (std::array<int, 10>{{0, 1, 3, 6, 10, 15, 21, 28, 36, 45}}));
86 }
87 //]
88