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 // UNSUPPORTED: libcpp-has-no-incomplete-ranges
11 
12 // Some basic examples of how transform_view might be used in the wild. This is a general
13 // collection of sample algorithms and functions that try to mock general usage of
14 // this view.
15 
16 #include <ranges>
17 
18 #include <cctype>
19 #include <functional>
20 #include <list>
21 #include <numeric>
22 #include <string>
23 #include <vector>
24 
25 #include <cassert>
26 #include "test_macros.h"
27 #include "test_iterators.h"
28 #include "types.h"
29 
30 template<class T, class F>
31 concept ValidTransformView = requires { typename std::ranges::transform_view<T, F>; };
32 
33 struct BadFunction { };
34 static_assert( ValidTransformView<MoveOnlyView, PlusOne>);
35 static_assert(!ValidTransformView<Range, PlusOne>);
36 static_assert(!ValidTransformView<MoveOnlyView, BadFunction>);
37 
38 template<std::ranges::range R>
39 auto toUpper(R range) {
40   return std::ranges::transform_view(range, [](char c) { return std::toupper(c); });
41 }
42 
43 template<class E1, class E2, size_t N, class Join = std::plus<E1>>
44 auto joinArrays(E1 (&a)[N], E2 (&b)[N], Join join = Join()) {
45   return std::ranges::transform_view(a, [&a, &b, join](auto& x) {
46     auto idx = (&x) - a;
47     return join(x, b[idx]);
48   });
49 }
50 
51 struct NonConstView : std::ranges::view_base {
52   explicit NonConstView(int *b, int *e) : b_(b), e_(e) {}
53   const int *begin() { return b_; }  // deliberately non-const
54   const int *end() { return e_; }    // deliberately non-const
55   const int *b_;
56   const int *e_;
57 };
58 
59 int main(int, char**) {
60   {
61     std::vector<int> vec = {1, 2, 3, 4};
62     auto transformed = std::ranges::transform_view(vec, [](int x) { return x + 42; });
63     int expected[] = {43, 44, 45, 46};
64     assert(std::equal(transformed.begin(), transformed.end(), expected, expected + 4));
65     const auto& ct = transformed;
66     assert(std::equal(ct.begin(), ct.end(), expected, expected + 4));
67   }
68 
69   {
70     // Test a view type that is not const-iterable.
71     int a[] = {1, 2, 3, 4};
72     auto transformed = NonConstView(a, a + 4) | std::views::transform([](int x) { return x + 42; });
73     int expected[4] = {43, 44, 45, 46};
74     assert(std::equal(transformed.begin(), transformed.end(), expected, expected + 4));
75   }
76 
77   {
78     int a[4] = {1, 2, 3, 4};
79     int b[4] = {4, 3, 2, 1};
80     auto out = joinArrays(a, b);
81     int check[4] = {5, 5, 5, 5};
82     assert(std::equal(out.begin(), out.end(), check, check + 4));
83   }
84 
85   {
86     std::string_view str = "Hello, World.";
87     auto upp = toUpper(str);
88     std::string_view check = "HELLO, WORLD.";
89     assert(std::equal(upp.begin(), upp.end(), check.begin(), check.end()));
90   }
91 
92   return 0;
93 }
94