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 drop_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 <vector>
19 #include <list>
20 #include <string>
21 
22 #include <cassert>
23 #include "test_macros.h"
24 #include "test_iterators.h"
25 #include "types.h"
26 
27 template<class T>
28 concept ValidDropView = requires { typename std::ranges::drop_view<T>; };
29 
30 static_assert( ValidDropView<MoveOnlyView>);
31 static_assert(!ValidDropView<Range>);
32 
33 static_assert(!std::ranges::enable_borrowed_range<std::ranges::drop_view<MoveOnlyView>>);
34 static_assert( std::ranges::enable_borrowed_range<std::ranges::drop_view<BorrowableView>>);
35 
36 template<std::ranges::view View>
37 bool orderedFibonacci(View v, int n = 1) {
38   if (v.size() < 3)
39     return true;
40 
41   if (v[2] != v[0] + v[1])
42     return false;
43 
44   return orderedFibonacci(std::ranges::drop_view(v.base(), n), n + 1);
45 }
46 
47 template<std::ranges::view View>
48 std::ranges::view auto makeEven(View v) {
49   return std::ranges::drop_view(v, v.size() % 2);
50 }
51 
52 template<std::ranges::view View, class T>
53 int indexOf(View v, T element) {
54   int index = 0;
55   for (auto e : v) {
56     if (e == element)
57       return index;
58     index++;
59   }
60   return -1;
61 }
62 
63 template<std::ranges::view View, class T>
64 std::ranges::view auto removeBefore(View v, T element) {
65   std::ranges::drop_view out(v, indexOf(v, element) + 1);
66   return View(out.begin(), out.end());
67 }
68 
69 template<>
70 constexpr bool std::ranges::enable_view<std::vector<int>> = true;
71 
72 template<>
73 constexpr bool std::ranges::enable_view<std::list<int>> = true;
74 
75 template<>
76 constexpr bool std::ranges::enable_view<std::string> = true;
77 
78 int main(int, char**) {
79   const std::vector vec = {1,1,2,3,5,8,13};
80   assert(orderedFibonacci(std::ranges::drop_view(vec, 0)));
81   const std::vector vec2 = {1,1,2,3,5,8,14};
82   assert(!orderedFibonacci(std::ranges::drop_view(vec2, 0)));
83 
84   const std::list l = {1, 2, 3};
85   auto el = makeEven(l);
86   assert(el.size() == 2);
87   assert(*el.begin() == 2);
88 
89   const std::string s = "Hello, World";
90   assert(removeBefore(s, ' ') == "World");
91 
92   return 0;
93 }
94