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// Core concepts and definitions for <ranges> -*- C++ -*-
// Copyright (C) 2019-2021 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.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file bits/ranges_base.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{ranges}
*/
#ifndef _GLIBCXX_RANGES_BASE_H
#define _GLIBCXX_RANGES_BASE_H 1
#pragma GCC system_header
#if __cplusplus > 201703L
#include <bits/iterator_concepts.h>
#include <ext/numeric_traits.h>
#include <bits/max_size_type.h>
#ifdef __cpp_lib_concepts
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace ranges
{
template<typename>
inline constexpr bool disable_sized_range = false;
template<typename _Tp>
inline constexpr bool enable_borrowed_range = false;
namespace __detail
{
constexpr __max_size_type
__to_unsigned_like(__max_size_type __t) noexcept
{ return __t; }
constexpr __max_size_type
__to_unsigned_like(__max_diff_type __t) noexcept
{ return __max_size_type(__t); }
template<integral _Tp>
constexpr auto
__to_unsigned_like(_Tp __t) noexcept
{ return static_cast<make_unsigned_t<_Tp>>(__t); }
#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
constexpr unsigned __int128
__to_unsigned_like(__int128 __t) noexcept
{ return __t; }
constexpr unsigned __int128
__to_unsigned_like(unsigned __int128 __t) noexcept
{ return __t; }
#endif
template<typename _Tp>
using __make_unsigned_like_t
= decltype(__detail::__to_unsigned_like(std::declval<_Tp>()));
// Part of the constraints of ranges::borrowed_range
template<typename _Tp>
concept __maybe_borrowed_range
= is_lvalue_reference_v<_Tp>
|| enable_borrowed_range<remove_cvref_t<_Tp>>;
} // namespace __detail
namespace __cust_access
{
using std::ranges::__detail::__maybe_borrowed_range;
using std::__detail::__range_iter_t;
struct _Begin
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (is_array_v<remove_reference_t<_Tp>>)
return true;
else if constexpr (__member_begin<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().begin()));
else
return noexcept(__decay_copy(begin(std::declval<_Tp&>())));
}
public:
template<__maybe_borrowed_range _Tp>
requires is_array_v<remove_reference_t<_Tp>> || __member_begin<_Tp>
|| __adl_begin<_Tp>
constexpr auto
operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
{
if constexpr (is_array_v<remove_reference_t<_Tp>>)
{
static_assert(is_lvalue_reference_v<_Tp>);
return __t + 0;
}
else if constexpr (__member_begin<_Tp>)
return __t.begin();
else
return begin(__t);
}
};
template<typename _Tp>
concept __member_end = requires(_Tp& __t)
{
{ __decay_copy(__t.end()) } -> sentinel_for<__range_iter_t<_Tp>>;
};
// Poison pills so that unqualified lookup doesn't find std::end.
void end(auto&) = delete;
void end(const auto&) = delete;
template<typename _Tp>
concept __adl_end = __class_or_enum<remove_reference_t<_Tp>>
&& requires(_Tp& __t)
{
{ __decay_copy(end(__t)) } -> sentinel_for<__range_iter_t<_Tp>>;
};
struct _End
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
return true;
else if constexpr (__member_end<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().end()));
else
return noexcept(__decay_copy(end(std::declval<_Tp&>())));
}
public:
template<__maybe_borrowed_range _Tp>
requires is_bounded_array_v<remove_reference_t<_Tp>>
|| __member_end<_Tp> || __adl_end<_Tp>
constexpr auto
operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
{
if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
{
static_assert(is_lvalue_reference_v<_Tp>);
return __t + extent_v<remove_reference_t<_Tp>>;
}
else if constexpr (__member_end<_Tp>)
return __t.end();
else
return end(__t);
}
};
// If _To is an lvalue-reference, return const _Tp&, otherwise const _Tp&&.
template<typename _To, typename _Tp>
constexpr decltype(auto)
__as_const(_Tp& __t) noexcept
{
static_assert(std::is_same_v<_To&, _Tp&>);
if constexpr (is_lvalue_reference_v<_To>)
return const_cast<const _Tp&>(__t);
else
return static_cast<const _Tp&&>(__t);
}
struct _CBegin
{
template<typename _Tp>
constexpr auto
operator()(_Tp&& __e) const
noexcept(noexcept(_Begin{}(__cust_access::__as_const<_Tp>(__e))))
requires requires { _Begin{}(__cust_access::__as_const<_Tp>(__e)); }
{
return _Begin{}(__cust_access::__as_const<_Tp>(__e));
}
};
struct _CEnd
{
template<typename _Tp>
constexpr auto
operator()(_Tp&& __e) const
noexcept(noexcept(_End{}(__cust_access::__as_const<_Tp>(__e))))
requires requires { _End{}(__cust_access::__as_const<_Tp>(__e)); }
{
return _End{}(__cust_access::__as_const<_Tp>(__e));
}
};
template<typename _Tp>
concept __member_rbegin = requires(_Tp& __t)
{
{ __decay_copy(__t.rbegin()) } -> input_or_output_iterator;
};
void rbegin(auto&) = delete;
void rbegin(const auto&) = delete;
template<typename _Tp>
concept __adl_rbegin = __class_or_enum<remove_reference_t<_Tp>>
&& requires(_Tp& __t)
{
{ __decay_copy(rbegin(__t)) } -> input_or_output_iterator;
};
template<typename _Tp>
concept __reversable = requires(_Tp& __t)
{
{ _Begin{}(__t) } -> bidirectional_iterator;
{ _End{}(__t) } -> same_as<decltype(_Begin{}(__t))>;
};
struct _RBegin
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (__member_rbegin<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().rbegin()));
else if constexpr (__adl_rbegin<_Tp>)
return noexcept(__decay_copy(rbegin(std::declval<_Tp&>())));
else
{
if constexpr (noexcept(_End{}(std::declval<_Tp&>())))
{
using _It = decltype(_End{}(std::declval<_Tp&>()));
// std::reverse_iterator copy-initializes its member.
return is_nothrow_copy_constructible_v<_It>;
}
else
return false;
}
}
public:
template<__maybe_borrowed_range _Tp>
requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
constexpr auto
operator()(_Tp&& __t) const
noexcept(_S_noexcept<_Tp&>())
{
if constexpr (__member_rbegin<_Tp>)
return __t.rbegin();
else if constexpr (__adl_rbegin<_Tp>)
return rbegin(__t);
else
return std::make_reverse_iterator(_End{}(__t));
}
};
template<typename _Tp>
concept __member_rend = requires(_Tp& __t)
{
{ __decay_copy(__t.rend()) }
-> sentinel_for<decltype(_RBegin{}(std::forward<_Tp>(__t)))>;
};
void rend(auto&) = delete;
void rend(const auto&) = delete;
template<typename _Tp>
concept __adl_rend = __class_or_enum<remove_reference_t<_Tp>>
&& requires(_Tp& __t)
{
{ __decay_copy(rend(__t)) }
-> sentinel_for<decltype(_RBegin{}(std::forward<_Tp>(__t)))>;
};
struct _REnd
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (__member_rend<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().rend()));
else if constexpr (__adl_rend<_Tp>)
return noexcept(__decay_copy(rend(std::declval<_Tp&>())));
else
{
if constexpr (noexcept(_Begin{}(std::declval<_Tp&>())))
{
using _It = decltype(_Begin{}(std::declval<_Tp&>()));
// std::reverse_iterator copy-initializes its member.
return is_nothrow_copy_constructible_v<_It>;
}
else
return false;
}
}
public:
template<__maybe_borrowed_range _Tp>
requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
constexpr auto
operator()(_Tp&& __t) const
noexcept(_S_noexcept<_Tp&>())
{
if constexpr (__member_rend<_Tp>)
return __t.rend();
else if constexpr (__adl_rend<_Tp>)
return rend(__t);
else
return std::make_reverse_iterator(_Begin{}(__t));
}
};
struct _CRBegin
{
template<typename _Tp>
constexpr auto
operator()(_Tp&& __e) const
noexcept(noexcept(_RBegin{}(__cust_access::__as_const<_Tp>(__e))))
requires requires { _RBegin{}(__cust_access::__as_const<_Tp>(__e)); }
{
return _RBegin{}(__cust_access::__as_const<_Tp>(__e));
}
};
struct _CREnd
{
template<typename _Tp>
constexpr auto
operator()(_Tp&& __e) const
noexcept(noexcept(_REnd{}(__cust_access::__as_const<_Tp>(__e))))
requires requires { _REnd{}(__cust_access::__as_const<_Tp>(__e)); }
{
return _REnd{}(__cust_access::__as_const<_Tp>(__e));
}
};
template<typename _Tp>
concept __member_size = !disable_sized_range<remove_cvref_t<_Tp>>
&& requires(_Tp& __t)
{
{ __decay_copy(__t.size()) } -> __detail::__is_integer_like;
};
void size(auto&) = delete;
void size(const auto&) = delete;
template<typename _Tp>
concept __adl_size = __class_or_enum<remove_reference_t<_Tp>>
&& !disable_sized_range<remove_cvref_t<_Tp>>
&& requires(_Tp& __t)
{
{ __decay_copy(size(__t)) } -> __detail::__is_integer_like;
};
template<typename _Tp>
concept __sentinel_size = requires(_Tp& __t)
{
requires (!is_unbounded_array_v<remove_reference_t<_Tp>>);
{ _Begin{}(__t) } -> forward_iterator;
{ _End{}(__t) } -> sized_sentinel_for<decltype(_Begin{}(__t))>;
__detail::__to_unsigned_like(_End{}(__t) - _Begin{}(__t));
};
struct _Size
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
return true;
else if constexpr (__member_size<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().size()));
else if constexpr (__adl_size<_Tp>)
return noexcept(__decay_copy(size(std::declval<_Tp&>())));
else if constexpr (__sentinel_size<_Tp>)
return noexcept(_End{}(std::declval<_Tp&>())
- _Begin{}(std::declval<_Tp&>()));
}
public:
template<typename _Tp>
requires is_bounded_array_v<remove_reference_t<_Tp>>
|| __member_size<_Tp> || __adl_size<_Tp> || __sentinel_size<_Tp>
constexpr auto
operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
{
if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
return extent_v<remove_reference_t<_Tp>>;
else if constexpr (__member_size<_Tp>)
return __t.size();
else if constexpr (__adl_size<_Tp>)
return size(__t);
else if constexpr (__sentinel_size<_Tp>)
return __detail::__to_unsigned_like(_End{}(__t) - _Begin{}(__t));
}
};
struct _SSize
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3403. Domain of ranges::ssize(E) doesn't match ranges::size(E)
template<typename _Tp>
requires requires (_Tp& __t) { _Size{}(__t); }
constexpr auto
operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
{
auto __size = _Size{}(__t);
using __size_type = decltype(__size);
// Return the wider of ptrdiff_t and make-signed-like-t<__size_type>.
if constexpr (integral<__size_type>)
{
using __gnu_cxx::__int_traits;
if constexpr (__int_traits<__size_type>::__digits
< __int_traits<ptrdiff_t>::__digits)
return static_cast<ptrdiff_t>(__size);
else
return static_cast<make_signed_t<__size_type>>(__size);
}
#if defined __STRICT_ANSI__ && defined __SIZEOF_INT128__
// For strict-ansi modes integral<__int128> is false
else if constexpr (__detail::__is_int128<__size_type>)
return static_cast<__int128>(__size);
#endif
else // Must be one of __max_diff_type or __max_size_type.
return __detail::__max_diff_type(__size);
}
};
template<typename _Tp>
concept __member_empty = requires(_Tp& __t) { bool(__t.empty()); };
template<typename _Tp>
concept __size0_empty = requires(_Tp& __t) { _Size{}(__t) == 0; };
template<typename _Tp>
concept __eq_iter_empty = requires(_Tp& __t)
{
requires (!is_unbounded_array_v<remove_reference_t<_Tp>>);
{ _Begin{}(__t) } -> forward_iterator;
bool(_Begin{}(__t) == _End{}(__t));
};
struct _Empty
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (__member_empty<_Tp>)
return noexcept(bool(std::declval<_Tp&>().empty()));
else if constexpr (__size0_empty<_Tp>)
return noexcept(_Size{}(std::declval<_Tp&>()) == 0);
else
return noexcept(bool(_Begin{}(std::declval<_Tp&>())
== _End{}(std::declval<_Tp&>())));
}
public:
template<typename _Tp>
requires __member_empty<_Tp> || __size0_empty<_Tp>
|| __eq_iter_empty<_Tp>
constexpr bool
operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
{
if constexpr (__member_empty<_Tp>)
return bool(__t.empty());
else if constexpr (__size0_empty<_Tp>)
return _Size{}(__t) == 0;
else
return bool(_Begin{}(__t) == _End{}(__t));
}
};
template<typename _Tp>
concept __pointer_to_object = is_pointer_v<_Tp>
&& is_object_v<remove_pointer_t<_Tp>>;
template<typename _Tp>
concept __member_data = requires(_Tp& __t)
{
{ __decay_copy(__t.data()) } -> __pointer_to_object;
};
template<typename _Tp>
concept __begin_data = contiguous_iterator<__range_iter_t<_Tp>>;
struct _Data
{
private:
template<typename _Tp>
static constexpr bool
_S_noexcept()
{
if constexpr (__member_data<_Tp>)
return noexcept(__decay_copy(std::declval<_Tp&>().data()));
else
return noexcept(_Begin{}(std::declval<_Tp&>()));
}
public:
template<__maybe_borrowed_range _Tp>
requires __member_data<_Tp> || __begin_data<_Tp>
constexpr auto
operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
{
if constexpr (__member_data<_Tp>)
return __t.data();
else
return std::to_address(_Begin{}(__t));
}
};
struct _CData
{
template<typename _Tp>
constexpr auto
operator()(_Tp&& __e) const
noexcept(noexcept(_Data{}(__cust_access::__as_const<_Tp>(__e))))
requires requires { _Data{}(__cust_access::__as_const<_Tp>(__e)); }
{
return _Data{}(__cust_access::__as_const<_Tp>(__e));
}
};
} // namespace __cust_access
inline namespace __cust
{
inline constexpr __cust_access::_Begin begin{};
inline constexpr __cust_access::_End end{};
inline constexpr __cust_access::_CBegin cbegin{};
inline constexpr __cust_access::_CEnd cend{};
inline constexpr __cust_access::_RBegin rbegin{};
inline constexpr __cust_access::_REnd rend{};
inline constexpr __cust_access::_CRBegin crbegin{};
inline constexpr __cust_access::_CREnd crend{};
inline constexpr __cust_access::_Size size{};
inline constexpr __cust_access::_SSize ssize{};
inline constexpr __cust_access::_Empty empty{};
inline constexpr __cust_access::_Data data{};
inline constexpr __cust_access::_CData cdata{};
}
/// [range.range] The range concept.
template<typename _Tp>
concept range = requires(_Tp& __t)
{
ranges::begin(__t);
ranges::end(__t);
};
/// [range.range] The borrowed_range concept.
template<typename _Tp>
concept borrowed_range
= range<_Tp> && __detail::__maybe_borrowed_range<_Tp>;
template<typename _Tp>
using iterator_t = std::__detail::__range_iter_t<_Tp>;
template<range _Range>
using sentinel_t = decltype(ranges::end(std::declval<_Range&>()));
template<range _Range>
using range_difference_t = iter_difference_t<iterator_t<_Range>>;
template<range _Range>
using range_value_t = iter_value_t<iterator_t<_Range>>;
template<range _Range>
using range_reference_t = iter_reference_t<iterator_t<_Range>>;
template<range _Range>
using range_rvalue_reference_t
= iter_rvalue_reference_t<iterator_t<_Range>>;
/// [range.sized] The sized_range concept.
template<typename _Tp>
concept sized_range = range<_Tp>
&& requires(_Tp& __t) { ranges::size(__t); };
template<sized_range _Range>
using range_size_t = decltype(ranges::size(std::declval<_Range&>()));
/// [range.view] The ranges::view_base type.
struct view_base { };
/// [range.view] The ranges::enable_view boolean.
template<typename _Tp>
inline constexpr bool enable_view = derived_from<_Tp, view_base>;
/// [range.view] The ranges::view concept.
template<typename _Tp>
concept view
= range<_Tp> && movable<_Tp> && enable_view<_Tp>;
// [range.refinements]
/// A range for which ranges::begin returns an output iterator.
template<typename _Range, typename _Tp>
concept output_range
= range<_Range> && output_iterator<iterator_t<_Range>, _Tp>;
/// A range for which ranges::begin returns an input iterator.
template<typename _Tp>
concept input_range = range<_Tp> && input_iterator<iterator_t<_Tp>>;
/// A range for which ranges::begin returns a forward iterator.
template<typename _Tp>
concept forward_range
= input_range<_Tp> && forward_iterator<iterator_t<_Tp>>;
/// A range for which ranges::begin returns a bidirectional iterator.
template<typename _Tp>
concept bidirectional_range
= forward_range<_Tp> && bidirectional_iterator<iterator_t<_Tp>>;
/// A range for which ranges::begin returns a random access iterator.
template<typename _Tp>
concept random_access_range
= bidirectional_range<_Tp> && random_access_iterator<iterator_t<_Tp>>;
/// A range for which ranges::begin returns a contiguous iterator.
template<typename _Tp>
concept contiguous_range
= random_access_range<_Tp> && contiguous_iterator<iterator_t<_Tp>>
&& requires(_Tp& __t)
{
{ ranges::data(__t) } -> same_as<add_pointer_t<range_reference_t<_Tp>>>;
};
/// A range for which ranges::begin and ranges::end return the same type.
template<typename _Tp>
concept common_range
= range<_Tp> && same_as<iterator_t<_Tp>, sentinel_t<_Tp>>;
/// A range which can be safely converted to a view.
template<typename _Tp>
concept viewable_range = range<_Tp>
&& ((view<remove_cvref_t<_Tp>> && constructible_from<remove_cvref_t<_Tp>, _Tp>)
|| (!view<remove_cvref_t<_Tp>> && borrowed_range<_Tp>));
// [range.iter.ops] range iterator operations
struct __advance_fn
{
template<input_or_output_iterator _It>
constexpr void
operator()(_It& __it, iter_difference_t<_It> __n) const
{
if constexpr (random_access_iterator<_It>)
__it += __n;
else if constexpr (bidirectional_iterator<_It>)
{
if (__n > 0)
{
do
{
++__it;
}
while (--__n);
}
else if (__n < 0)
{
do
{
--__it;
}
while (++__n);
}
}
else
{
// cannot decrement a non-bidirectional iterator
__glibcxx_assert(__n >= 0);
while (__n-- > 0)
++__it;
}
}
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
constexpr void
operator()(_It& __it, _Sent __bound) const
{
if constexpr (assignable_from<_It&, _Sent>)
__it = std::move(__bound);
else if constexpr (sized_sentinel_for<_Sent, _It>)
(*this)(__it, __bound - __it);
else
{
while (__it != __bound)
++__it;
}
}
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
constexpr iter_difference_t<_It>
operator()(_It& __it, iter_difference_t<_It> __n, _Sent __bound) const
{
if constexpr (sized_sentinel_for<_Sent, _It>)
{
const auto __diff = __bound - __it;
if (__diff == 0)
return __n;
else if (__diff > 0 ? __n >= __diff : __n <= __diff)
{
(*this)(__it, __bound);
return __n - __diff;
}
else if (__n != 0) [[likely]]
{
// n and bound must not lead in opposite directions:
__glibcxx_assert(__n < 0 == __diff < 0);
(*this)(__it, __n);
return 0;
}
else
return 0;
}
else if (__it == __bound || __n == 0)
return __n;
else if (__n > 0)
{
iter_difference_t<_It> __m = 0;
do
{
++__it;
++__m;
}
while (__m != __n && __it != __bound);
return __n - __m;
}
else if constexpr (bidirectional_iterator<_It> && same_as<_It, _Sent>)
{
iter_difference_t<_It> __m = 0;
do
{
--__it;
--__m;
}
while (__m != __n && __it != __bound);
return __n - __m;
}
else
{
// cannot decrement a non-bidirectional iterator
__glibcxx_assert(__n >= 0);
return __n;
}
}
};
inline constexpr __advance_fn advance{};
struct __distance_fn
{
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
constexpr iter_difference_t<_It>
operator()(_It __first, _Sent __last) const
{
if constexpr (sized_sentinel_for<_Sent, _It>)
return __last - __first;
else
{
iter_difference_t<_It> __n = 0;
while (__first != __last)
{
++__first;
++__n;
}
return __n;
}
}
template<range _Range>
constexpr range_difference_t<_Range>
operator()(_Range&& __r) const
{
if constexpr (sized_range<_Range>)
return static_cast<range_difference_t<_Range>>(ranges::size(__r));
else
return (*this)(ranges::begin(__r), ranges::end(__r));
}
};
inline constexpr __distance_fn distance{};
struct __next_fn
{
template<input_or_output_iterator _It>
constexpr _It
operator()(_It __x) const
{
++__x;
return __x;
}
template<input_or_output_iterator _It>
constexpr _It
operator()(_It __x, iter_difference_t<_It> __n) const
{
ranges::advance(__x, __n);
return __x;
}
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
constexpr _It
operator()(_It __x, _Sent __bound) const
{
ranges::advance(__x, __bound);
return __x;
}
template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
constexpr _It
operator()(_It __x, iter_difference_t<_It> __n, _Sent __bound) const
{
ranges::advance(__x, __n, __bound);
return __x;
}
};
inline constexpr __next_fn next{};
struct __prev_fn
{
template<bidirectional_iterator _It>
constexpr _It
operator()(_It __x) const
{
--__x;
return __x;
}
template<bidirectional_iterator _It>
constexpr _It
operator()(_It __x, iter_difference_t<_It> __n) const
{
ranges::advance(__x, -__n);
return __x;
}
template<bidirectional_iterator _It>
constexpr _It
operator()(_It __x, iter_difference_t<_It> __n, _It __bound) const
{
ranges::advance(__x, -__n, __bound);
return __x;
}
};
inline constexpr __prev_fn prev{};
/// Type returned by algorithms instead of a dangling iterator or subrange.
struct dangling
{
constexpr dangling() noexcept = default;
template<typename... _Args>
constexpr dangling(_Args&&...) noexcept { }
};
template<range _Range>
using borrowed_iterator_t = conditional_t<borrowed_range<_Range>,
iterator_t<_Range>,
dangling>;
} // namespace ranges
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // library concepts
#endif // C++20
#endif // _GLIBCXX_RANGES_BASE_H
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