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// UNSUPPORTED: c++03, c++11, c++14, c++17
10
11// constexpr auto begin() requires (!simple-view<V>)
12// constexpr auto begin() const requires range<const V>
13
14#include <cassert>
15#include <concepts>
16#include <ranges>
17#include <tuple>
18#include <utility>
19
20#include "types.h"
21
22template <class T>
23concept HasConstBegin = requires(const T ct) { ct.begin(); };
24
25template <class T>
26concept HasBegin = requires(T t) { t.begin(); };
27
28template <class T>
29concept HasConstAndNonConstBegin =
30 HasConstBegin<T> &&
31 // because const begin and non-const begin returns different types (iterator<true>, iterator<false>)
32 requires(T t, const T ct) { requires !std::same_as<decltype(t.begin()), decltype(ct.begin())>; };
33
34template <class T>
35concept HasOnlyNonConstBegin = HasBegin<T> && !HasConstBegin<T>;
36
37template <class T>
38concept HasOnlyConstBegin = HasConstBegin<T> && !HasConstAndNonConstBegin<T>;
39
40struct NoConstBeginView : TupleBufferView {
41 using TupleBufferView::TupleBufferView;
42 constexpr std::tuple<int>* begin() { return buffer_; }
43 constexpr std::tuple<int>* end() { return buffer_ + size_; }
44};
45
46// simple-view<V>
47static_assert(HasOnlyConstBegin<std::ranges::elements_view<SimpleCommon, 0>>);
48
49// !simple-view<V> && range<const V>
50static_assert(HasConstAndNonConstBegin<std::ranges::elements_view<NonSimpleCommon, 0>>);
51
52// !range<const V>
53static_assert(HasOnlyNonConstBegin<std::ranges::elements_view<NoConstBeginView, 0>>);
54
55constexpr bool test() {
56 std::tuple<int> buffer[] = {{1}, {2}};
57 {
58 // underlying iterator should be pointing to the first element
59 auto ev = std::views::elements<0>(buffer);
60 auto iter = ev.begin();
61 assert(&(*iter) == &std::get<0>(buffer[0]));
62 }
63
64 {
65 // underlying range models simple-view
66 auto v = std::views::elements<0>(SimpleCommon{buffer});
67 static_assert(std::is_same_v<decltype(v.begin()), decltype(std::as_const(v).begin())>);
68 assert(v.begin() == std::as_const(v).begin());
69 auto&& r = *std::as_const(v).begin();
70 assert(&r == &std::get<0>(buffer[0]));
71 }
72
73 {
74 // underlying const R is not a range
75 auto v = std::views::elements<0>(NoConstBeginView{buffer});
76 auto&& r = *v.begin();
77 assert(&r == &std::get<0>(buffer[0]));
78 }
79
80 return true;
81}
82
83int main(int, char**) {
84 test();
85 static_assert(test());
86
87 return 0;
88}
89

source code of libcxx/test/std/ranges/range.adaptors/range.elements/begin.pass.cpp