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// Some basic examples of how drop_view might be used in the wild. This is a general
12// collection of sample algorithms and functions that try to mock general usage of
13// this view.
14
15#include <ranges>
16
17#include <vector>
18#include <list>
19#include <string>
20
21#include <cassert>
22#include "test_macros.h"
23#include "test_iterators.h"
24#include "types.h"
25
26template<class T>
27concept ValidDropView = requires { typename std::ranges::drop_view<T>; };
28
29static_assert( ValidDropView<MoveOnlyView>);
30static_assert(!ValidDropView<Range>);
31
32static_assert(!std::ranges::enable_borrowed_range<std::ranges::drop_view<MoveOnlyView>>);
33static_assert( std::ranges::enable_borrowed_range<std::ranges::drop_view<BorrowableView>>);
34
35template<std::ranges::view View>
36bool orderedFibonacci(View v, int n = 1) {
37 if (v.size() < 3)
38 return true;
39
40 if (v[2] != v[0] + v[1])
41 return false;
42
43 return orderedFibonacci(std::ranges::drop_view(v.base(), n), n + 1);
44}
45
46template<std::ranges::view View>
47std::ranges::view auto makeEven(View v) {
48 return std::ranges::drop_view(v, v.size() % 2);
49}
50
51template<std::ranges::view View, class T>
52int indexOf(View v, T element) {
53 int index = 0;
54 for (auto e : v) {
55 if (e == element)
56 return index;
57 index++;
58 }
59 return -1;
60}
61
62template<std::ranges::view View, class T>
63std::ranges::view auto removeBefore(View v, T element) {
64 std::ranges::drop_view out(v, indexOf(v, element) + 1);
65 return View(out.begin(), out.end());
66}
67
68template<>
69constexpr bool std::ranges::enable_view<std::vector<int>> = true;
70
71template<>
72constexpr bool std::ranges::enable_view<std::list<int>> = true;
73
74template<>
75constexpr bool std::ranges::enable_view<std::string> = true;
76
77int main(int, char**) {
78 const std::vector vec = {1,1,2,3,5,8,13};
79 assert(orderedFibonacci(std::ranges::drop_view(vec, 0)));
80 const std::vector vec2 = {1,1,2,3,5,8,14};
81 assert(!orderedFibonacci(std::ranges::drop_view(vec2, 0)));
82
83 const std::list l = {1, 2, 3};
84 auto el = makeEven(l);
85 assert(el.size() == 2);
86 assert(*el.begin() == 2);
87
88 const std::string s = "Hello, World";
89 assert(removeBefore(s, ' ') == "World");
90
91 return 0;
92}
93

source code of libcxx/test/std/ranges/range.adaptors/range.drop/general.pass.cpp