1//===----------------------------------------------------------------------===//
 2//
 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 4// See https://llvm.org/LICENSE.txt for license information.
 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 6//
 7//===----------------------------------------------------------------------===//
 8
 9#ifndef _LIBCPP___ITERATOR_PRODUCT_ITERATOR_H
10#define _LIBCPP___ITERATOR_PRODUCT_ITERATOR_H
11
12// Product iterators are iterators that contain two or more underlying iterators.
13//
14// For example, std::flat_map stores its data into two separate containers, and its iterator
15// is a proxy over two separate underlying iterators. The concept of product iterators
16// allows algorithms to operate over these underlying iterators separately, opening the
17// door to various optimizations.
18//
19// If __product_iterator_traits can be instantiated, the following functions and associated types must be provided:
20// - static constexpr size_t Traits::__size
21//   The number of underlying iterators inside the product iterator.
22//
23// - template <size_t _N>
24//   static decltype(auto) Traits::__get_iterator_element(It&& __it)
25//   Returns the _Nth iterator element of the given product iterator.
26//
27// - template <class... _Iters>
28//   static _Iterator __make_product_iterator(_Iters&&...);
29//   Creates a product iterator from the given underlying iterators.
30
31#include <__config>
32#include <__cstddef/size_t.h>
33#include <__type_traits/enable_if.h>
34#include <__type_traits/integral_constant.h>
35#include <__utility/declval.h>
36
37#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
38#  pragma GCC system_header
39#endif
40
41_LIBCPP_BEGIN_NAMESPACE_STD
42
43template <class _Iterator>
44struct __product_iterator_traits;
45/* exposition-only:
46{
47  static constexpr size_t __size = ...;
48
49  template <size_t _N, class _Iter>
50  static decltype(auto) __get_iterator_element(_Iter&&);
51
52  template <class... _Iters>
53  static _Iterator __make_product_iterator(_Iters&&...);
54};
55*/
56
57template <class _Tp, size_t = 0>
58struct __is_product_iterator : false_type {};
59
60template <class _Tp>
61struct __is_product_iterator<_Tp, sizeof(__product_iterator_traits<_Tp>) * 0> : true_type {};
62
63template <class _Tp, size_t _Size, class = void>
64struct __is_product_iterator_of_size : false_type {};
65
66template <class _Tp, size_t _Size>
67struct __is_product_iterator_of_size<_Tp, _Size, __enable_if_t<__product_iterator_traits<_Tp>::__size == _Size> >
68    : true_type {};
69
70template <class _Iterator, size_t _Nth>
71using __product_iterator_element_t _LIBCPP_NODEBUG =
72    decltype(__product_iterator_traits<_Iterator>::template __get_iterator_element<_Nth>(std::declval<_Iterator>()));
73
74_LIBCPP_END_NAMESPACE_STD
75
76#endif // _LIBCPP___ITERATOR_PRODUCT_ITERATOR_H