libstdc++-v3/testsuite/std/ranges/adaptors/drop.cc

// Copyright (C) 2020-2021 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-options "-std=gnu++2a" }
// { dg-do run { target c++2a } }

#include <algorithm>
#include <ranges>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>

using __gnu_test::test_range;
using __gnu_test::forward_iterator_wrapper;
using __gnu_test::bidirectional_iterator_wrapper;
using __gnu_test::random_access_iterator_wrapper;

namespace ranges = std::ranges;
namespace views = ranges::views;

void
test01()
{
  int x[] = {1,2,3,4,5};
  auto v = x | views::drop(3);
  using R = decltype(v);
  static_assert(ranges::view<R>);
  static_assert(ranges::sized_range<R>);
  static_assert(ranges::random_access_range<R>);
  VERIFY( ranges::equal(v, (int[]){4,5}) );
}

void
test02()
{
  int x[] = {1,2,3,4,5};
  auto t = views::drop(3) | views::reverse;
  auto v = x | t;
  using R = decltype(v);
  static_assert(ranges::view<R>);
  static_assert(ranges::sized_range<R>);
  static_assert(ranges::random_access_range<R>);
  VERIFY( ranges::equal(v, (int[]){5,4}) );
}

void
test03()
{
  int x[] = {1,2,3,4,5};
  test_range<int, bidirectional_iterator_wrapper> rx(x);
  auto v = rx | views::drop(3);
  using R = decltype(v);
  static_assert(ranges::view<R>);
  static_assert(!ranges::sized_range<R>);
  static_assert(ranges::bidirectional_range<R>);
  VERIFY( ranges::equal(v, (int[]){4,5}) );
}


void
test04()
{
  auto v = views::iota(0) | views::drop(10);
  using R = decltype(v);
  static_assert(ranges::view<R>);
  static_assert(!ranges::sized_range<R>);
  VERIFY( ranges::equal(v | views::take(3), (int[]){10,11,12}) );
}

void
test05()
{
  int x[] = {1,2,3};
  auto r = ranges::subrange(x, x+1);
  auto v = views::drop(r, 2);
  VERIFY( ranges::begin(v) == x+1 );
  VERIFY( ranges::size(v) == 0 );
}

void
test06()
{
  int x[] = {1,2,3};
  VERIFY( ranges::empty(x | views::drop(10)) );
}

// The following tests that drop_view::begin caches its result.

template<typename T>
struct test_wrapper : forward_iterator_wrapper<T>
{
  static inline int increment_count = 0;

  using forward_iterator_wrapper<T>::forward_iterator_wrapper;

  test_wrapper() : forward_iterator_wrapper<T>()
  { }

  test_wrapper
  operator++(int)
  {
    auto tmp = *this;
    ++*this;
    return tmp;
  }

  test_wrapper&
  operator++()
  {
    ++increment_count;
    forward_iterator_wrapper<T>::operator++();
    return *this;
  }
};

void
test07()
{
  int x[] = {1,2,3,4,5};
  test_range<int, test_wrapper> rx(x);
  auto v = rx | views::drop(3);
  VERIFY( test_wrapper<int>::increment_count == 0 );
  (void) v.begin();
  VERIFY( test_wrapper<int>::increment_count == 3 );
  (void) v.begin();
  VERIFY( test_wrapper<int>::increment_count == 3 );
  VERIFY( ranges::equal(v, (int[]){4,5}) );
  VERIFY( test_wrapper<int>::increment_count == 5 );
  VERIFY( ranges::equal(v, (int[]){4,5}) );
  VERIFY( test_wrapper<int>::increment_count == 7 );
}

template<typename T>
struct ra_test_wrapper : random_access_iterator_wrapper<T>
{
  static inline int increment_count = 0;

  using random_access_iterator_wrapper<T>::random_access_iterator_wrapper;

  ra_test_wrapper() : random_access_iterator_wrapper<T>()
  { }

  ra_test_wrapper
  operator++(int)
  {
    auto tmp = *this;
    ++*this;
    return tmp;
  }

  ra_test_wrapper&
  operator++()
  {
    ++increment_count;
    random_access_iterator_wrapper<T>::operator++();
    return *this;
  }

  ra_test_wrapper
  operator--(int)
  {
    auto tmp = *this;
    --*this;
    return tmp;
  }

  ra_test_wrapper&
  operator--()
  {
    random_access_iterator_wrapper<T>::operator--();
    return *this;
  }

  ra_test_wrapper&
  operator+=(std::ptrdiff_t n)
  {
    random_access_iterator_wrapper<T>::operator+=(n);
    return *this;
  }

  ra_test_wrapper&
  operator-=(std::ptrdiff_t n)
  { return *this += -n; }

  ra_test_wrapper
  operator+(std::ptrdiff_t n) const
  {
    auto tmp = *this;
    return tmp += n;
  }

  ra_test_wrapper
  operator-(std::ptrdiff_t n) const
  {
    auto tmp = *this;
    return tmp -= n;
  }

  std::ptrdiff_t
  operator-(const ra_test_wrapper& it) const
  {
    return static_cast<const random_access_iterator_wrapper<T>&>(*this) - it;
  }

  friend ra_test_wrapper
  operator+(std::ptrdiff_t n, const ra_test_wrapper& it)
  { return it + n; }
};

void
test08()
{
  // LWG 3482 - drop_view's const begin should additionally require sized_range

  short a[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
  test_range<short, ra_test_wrapper> ra(a);
  static_assert( ranges::random_access_range<decltype(ra)> );
  ranges::subrange nonsized = {ra.begin(), std::unreachable_sentinel};
  using Nonsized = decltype(nonsized);
  static_assert( ranges::random_access_range<Nonsized> );
  static_assert( ! ranges::sized_range<Nonsized> );
  auto v1 = nonsized | views::drop(5);
  VERIFY( ra_test_wrapper<short>::increment_count == 0 );
  auto b1 = v1.begin();
  VERIFY( ra_test_wrapper<short>::increment_count == 5 );
  VERIFY( v1.begin() == b1 );
  VERIFY( ra_test_wrapper<short>::increment_count == 5 );
  VERIFY( *b1 == 5 );
  VERIFY( *v1.begin() == 5 );
  VERIFY( ra_test_wrapper<short>::increment_count == 5 );

  long b[10]{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
  test_range<long, ra_test_wrapper> rb(b);
  ranges::subrange sized = {rb.begin(), rb.begin()+6};
  using Sized = decltype(sized);
  static_assert( ranges::random_access_range<Sized> );
  static_assert( ranges::sized_range<Sized> );
  auto v2 = sized | views::drop(6);
  auto b2 = v2.begin();
  VERIFY( ra_test_wrapper<long>::increment_count == 0 );
  VERIFY( v2.begin() == b2 );
  VERIFY( ra_test_wrapper<long>::increment_count == 0 );
  VERIFY( *b2 == 6 );
  VERIFY( *v2.begin() == 6 );
  VERIFY( ra_test_wrapper<long>::increment_count == 0 );
}

template<auto drop = views::drop>
void
test09()
{
  // Verify SFINAE behavior.
  extern int x[5];
  int* n = 0;
  static_assert(!requires { drop(); });
  static_assert(!requires { drop(x, n, n); });
  static_assert(!requires { drop(x, n); });
  static_assert(!requires { drop(n)(x); });
  static_assert(!requires { x | (drop(n) | views::all); });
  static_assert(!requires { (drop(n) | views::all)(x); });
  static_assert(!requires { drop | views::all; });
  static_assert(!requires { views::all | drop; });
}

int
main()
{
  test01();
  test02();
  test03();
  test04();
  test05();
  test06();
  test07();
  test08();
  test09();
}