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
22 template <class T>
23 concept HasConstBegin = requires(const T ct) { ct.begin(); };
24
25 template <class T>
26 concept HasBegin = requires(T t) { t.begin(); };
27
28 template <class T>
29 concept 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
34 template <class T>
35 concept HasOnlyNonConstBegin = HasBegin<T> && !HasConstBegin<T>;
36
37 template <class T>
38 concept HasOnlyConstBegin = HasConstBegin<T> && !HasConstAndNonConstBegin<T>;
39
40 struct NoConstBeginView : TupleBufferView {
41 using TupleBufferView::TupleBufferView;
beginNoConstBeginView42 constexpr std::tuple<int>* begin() { return buffer_; }
endNoConstBeginView43 constexpr std::tuple<int>* end() { return buffer_ + size_; }
44 };
45
46 // simple-view<V>
47 static_assert(HasOnlyConstBegin<std::ranges::elements_view<SimpleCommon, 0>>);
48
49 // !simple-view<V> && range<const V>
50 static_assert(HasConstAndNonConstBegin<std::ranges::elements_view<NonSimpleCommon, 0>>);
51
52 // !range<const V>
53 static_assert(HasOnlyNonConstBegin<std::ranges::elements_view<NoConstBeginView, 0>>);
54
test()55 constexpr 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
main(int,char **)83 int main(int, char**) {
84 test();
85 static_assert(test());
86
87 return 0;
88 }
89