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-no-concepts
11 // UNSUPPORTED: libcpp-has-no-incomplete-ranges
12 
13 // Some basic examples of how drop_view might be used in the wild. This is a general
14 // collection of sample algorithms and functions that try to mock general usage of
15 // this view.
16 
17 #include <ranges>
18 
19 #include <vector>
20 #include <list>
21 #include <string>
22 
23 #include <cassert>
24 #include "test_macros.h"
25 #include "test_iterators.h"
26 #include "types.h"
27 
28 template<class T>
29 concept ValidDropView = requires { typename std::ranges::drop_view<T>; };
30 
31 static_assert( ValidDropView<MoveOnlyView>);
32 static_assert(!ValidDropView<Range>);
33 
34 static_assert(!std::ranges::enable_borrowed_range<std::ranges::drop_view<MoveOnlyView>>);
35 static_assert( std::ranges::enable_borrowed_range<std::ranges::drop_view<BorrowableView>>);
36 
37 template<std::ranges::view View>
38 bool orderedFibonacci(View v, int n = 1) {
39   if (v.size() < 3)
40     return true;
41 
42   if (v[2] != v[0] + v[1])
43     return false;
44 
45   return orderedFibonacci(std::ranges::drop_view(v.base(), n), n + 1);
46 }
47 
48 template<std::ranges::view View>
49 std::ranges::view auto makeEven(View v) {
50   return std::ranges::drop_view(v, v.size() % 2);
51 }
52 
53 template<std::ranges::view View, class T>
54 int indexOf(View v, T element) {
55   int index = 0;
56   for (auto e : v) {
57     if (e == element)
58       return index;
59     index++;
60   }
61   return -1;
62 }
63 
64 template<std::ranges::view View, class T>
65 std::ranges::view auto removeBefore(View v, T element) {
66   std::ranges::drop_view out(v, indexOf(v, element) + 1);
67   return View(out.begin(), out.end());
68 }
69 
70 template<>
71 constexpr bool std::ranges::enable_view<std::vector<int>> = true;
72 
73 template<>
74 constexpr bool std::ranges::enable_view<std::list<int>> = true;
75 
76 template<>
77 constexpr bool std::ranges::enable_view<std::string> = true;
78 
79 int main(int, char**) {
80   const std::vector vec = {1,1,2,3,5,8,13};
81   assert(orderedFibonacci(std::ranges::drop_view(vec, 0)));
82   const std::vector vec2 = {1,1,2,3,5,8,14};
83   assert(!orderedFibonacci(std::ranges::drop_view(vec2, 0)));
84 
85   const std::list l = {1, 2, 3};
86   auto el = makeEven(l);
87   assert(el.size() == 2);
88   assert(*el.begin() == 2);
89 
90   const std::string s = "Hello, World";
91   assert(removeBefore(s, ' ') == "World");
92 
93   return 0;
94 }
95