libstdc++-v3/testsuite/std/ranges/single_view.cc

// Copyright (C) 2019-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3.  If not see
// <http://www.gnu.org/licenses/>.

// { dg-do run { target c++20 } }

#include <ranges>
#include <utility> // as_const
#include <testsuite_hooks.h>

void
test01()
{
  std::ranges::single_view s{4};
  static_assert(std::same_as<std::ranges::range_value_t<decltype(s)>, int>);
  static_assert(std::ranges::size(s) == 1);

  int count = 0;
  for (auto i : s)
    ++count;
  VERIFY(count == 1);
  VERIFY(*std::ranges::begin(s) == 4);
}

void
test02()
{
  std::ranges::single_view<long> s2;
  static_assert(std::same_as<std::ranges::range_value_t<decltype(s2)>, long>);
  static_assert(std::ranges::size(s2) == 1);

  int count = 0;
  for (auto l : s2)
    ++count;
  VERIFY(count == 1);
  VERIFY(*std::ranges::begin(s2) == 0L);
}

void
test03()
{
  auto s3 = std::ranges::views::single('a');
  static_assert(std::same_as<std::ranges::range_value_t<decltype(s3)>, char>);
  static_assert(std::ranges::size(s3) == 1);
  VERIFY(*std::ranges::begin(s3) == 'a');
}

void
test04()
{
  // PR libstdc++/100475
  struct A {
    A() = default;
    A(int, int) { }
    A(std::initializer_list<int>) = delete;
    void operator&() const = delete;
  };
  std::ranges::single_view<A> s(std::in_place, 0, 0);
  s.data();
  std::as_const(s).data();
}

void
test05()
{
  int i = 0;
  static_assert(noexcept(std::ranges::single_view<int>()));
  static_assert(noexcept(std::ranges::single_view<int>(i)));
  static_assert(noexcept(std::ranges::single_view<int>(1)));
  static_assert(noexcept(std::ranges::single_view<int>(std::in_place, 2)));
  static_assert(noexcept(std::ranges::views::single(i)));
  auto s = std::ranges::views::single(i);
  static_assert(noexcept(s.begin()));
  static_assert(noexcept(s.end()));
  static_assert(noexcept(s.size()));
  static_assert(noexcept(s.data()));
  static_assert(noexcept(s.empty())); // view_interface::empty()
  const auto cs = s;
  static_assert(noexcept(cs.begin()));
  static_assert(noexcept(cs.end()));
  static_assert(noexcept(cs.size()));
  static_assert(noexcept(cs.data()));
  static_assert(noexcept(cs.empty())); // view_interface::empty()
}

void
test06()
{
  // PR libstdc++/100475 comment #7
  struct S {
    S() = default;
    S(std::initializer_list<S>) = delete;
    S(const S&) {}
  };
  S obj;
  auto x = std::views::single(obj);
  auto y = std::views::single(std::move(obj));
}

template<auto single = std::views::single>
void
test07()
{
  // Verify SFINAE behavior.
  struct uncopyable {
    uncopyable();
    uncopyable(const uncopyable&) = delete;
  };
  static_assert(!requires { single(uncopyable{}); });
}

template<auto single = std::views::single>
void
test08()
{
  struct move_only {
    move_only() { }
    move_only(move_only&&) { }
  };
#if __cpp_lib_ranges >= 202207L
  // P2494R2 Relaxing range adaptors to allow for move only types
  static_assert( requires { single(move_only{}); } );
#else
  static_assert( ! requires { single(move_only{}); } );
#endif
}

int main()
{
  test01();
  test02();
  test03();
  test04();
  test05();
  test06();
  test07();
  test08();
}