libstdc++-v3/include/bits/utility.h

// Utilities used throughout the library -*- C++ -*-

// Copyright (C) 2004-2025 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 include/bits/utility.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{utility}
 *
 *  This file contains the parts of `<utility>` needed by other headers,
 *  so they don't need to include the whole of `<utility>`.
 */

#ifndef _GLIBCXX_UTILITY_H
#define _GLIBCXX_UTILITY_H 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#if __cplusplus >= 201103L

#include <type_traits>
#include <bits/move.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /// Finds the size of a given tuple type.
  template<typename _Tp>
    struct tuple_size;

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2313. tuple_size should always derive from integral_constant<size_t, N>
  // 2770. tuple_size<const T> specialization is not SFINAE compatible

  template<typename _Tp,
	   typename _Up = typename remove_cv<_Tp>::type,
	   typename = typename enable_if<is_same<_Tp, _Up>::value>::type,
	   size_t = tuple_size<_Tp>::value>
    using __enable_if_has_tuple_size = _Tp;

  template<typename _Tp>
    struct tuple_size<const __enable_if_has_tuple_size<_Tp>>
    : public tuple_size<_Tp> { };

  template<typename _Tp>
    struct tuple_size<volatile __enable_if_has_tuple_size<_Tp>>
    : public tuple_size<_Tp> { };

  template<typename _Tp>
    struct tuple_size<const volatile __enable_if_has_tuple_size<_Tp>>
    : public tuple_size<_Tp> { };

#if __cplusplus >= 201703L
  template<typename _Tp>
    inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value;
#endif

  /// Gives the type of the ith element of a given tuple type.
  template<size_t __i, typename _Tp>
    struct tuple_element;

  // Duplicate of C++14's tuple_element_t for internal use in C++11 mode
  template<size_t __i, typename _Tp>
    using __tuple_element_t = typename tuple_element<__i, _Tp>::type;

  template<size_t __i, typename _Tp>
    struct tuple_element<__i, const _Tp>
    {
      using type = const __tuple_element_t<__i, _Tp>;
    };

  template<size_t __i, typename _Tp>
    struct tuple_element<__i, volatile _Tp>
    {
      using type = volatile __tuple_element_t<__i, _Tp>;
    };

  template<size_t __i, typename _Tp>
    struct tuple_element<__i, const volatile _Tp>
    {
      using type = const volatile __tuple_element_t<__i, _Tp>;
    };

#if __cplusplus >= 201402L

  // Return the index of _Tp in _Types, if it occurs exactly once.
  // Otherwise, return sizeof...(_Types).
  template<typename _Tp, typename... _Types>
    constexpr size_t
    __find_uniq_type_in_pack()
    {
      constexpr size_t __sz = sizeof...(_Types);
      constexpr bool __found[__sz] = { __is_same(_Tp, _Types) ... };
      size_t __n = __sz;
      for (size_t __i = 0; __i < __sz; ++__i)
	{
	  if (__found[__i])
	    {
	      if (__n < __sz) // more than one _Tp found
		return __sz;
	      __n = __i;
	    }
	}
      return __n;
    }
#endif // C++14

// The standard says this macro and alias template should be in <tuple> but we
// define them here, to be available in <array>, <utility> and <ranges> too.
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3378. tuple_size_v/tuple_element_t should be available when
//       tuple_size/tuple_element are
#ifdef __glibcxx_tuple_element_t // C++ >= 14
  template<size_t __i, typename _Tp>
    using tuple_element_t = typename tuple_element<__i, _Tp>::type;
#endif

  // Stores a tuple of indices.  Used by tuple and pair, and by bind() to
  // extract the elements in a tuple.
  template<size_t... _Indexes> struct _Index_tuple { };

  // Builds an _Index_tuple<0, 1, 2, ..., _Num-1>.
  template<size_t _Num>
    struct _Build_index_tuple
    {
#if __has_builtin(__make_integer_seq)
      template<typename, size_t... _Indices>
	using _IdxTuple = _Index_tuple<_Indices...>;

      // Clang defines __make_integer_seq for this purpose.
      using __type = __make_integer_seq<_IdxTuple, size_t, _Num>;
#else
      // For GCC and other compilers, use __integer_pack instead.
      using __type = _Index_tuple<__integer_pack(_Num)...>;
#endif
    };

#ifdef __glibcxx_integer_sequence // C++ >= 14

  /// Class template integer_sequence
  template<typename _Tp, _Tp... _Idx>
    struct integer_sequence
    {
#if __cplusplus >= 202002L
      static_assert(is_integral_v<_Tp>);
#endif
      typedef _Tp value_type;
      static constexpr size_t size() noexcept { return sizeof...(_Idx); }
    };

  /// Alias template make_integer_sequence
  template<typename _Tp, _Tp _Num>
    using make_integer_sequence
#if __has_builtin(__make_integer_seq)
      = __make_integer_seq<integer_sequence, _Tp, _Num>;
#else
      = integer_sequence<_Tp, __integer_pack(_Num)...>;
#endif

  /// Alias template index_sequence
  template<size_t... _Idx>
    using index_sequence = integer_sequence<size_t, _Idx...>;

  /// Alias template make_index_sequence
  template<size_t _Num>
    using make_index_sequence = make_integer_sequence<size_t, _Num>;

  /// Alias template index_sequence_for
  template<typename... _Types>
    using index_sequence_for = make_index_sequence<sizeof...(_Types)>;
#endif // __glibcxx_integer_sequence

#if __cplusplus >= 201703L

  struct in_place_t {
    explicit in_place_t() = default;
  };

  inline constexpr in_place_t in_place{};

  template<typename _Tp> struct in_place_type_t
  {
    explicit in_place_type_t() = default;
  };

  template<typename _Tp>
    inline constexpr in_place_type_t<_Tp> in_place_type{};

  template<size_t _Idx> struct in_place_index_t
  {
    explicit in_place_index_t() = default;
  };

  template<size_t _Idx>
    inline constexpr in_place_index_t<_Idx> in_place_index{};

  template<typename>
    inline constexpr bool __is_in_place_type_v = false;

  template<typename _Tp>
    inline constexpr bool __is_in_place_type_v<in_place_type_t<_Tp>> = true;

  template<typename>
    inline constexpr bool __is_in_place_index_v = false;

  template<size_t _Nm>
    inline constexpr bool __is_in_place_index_v<in_place_index_t<_Nm>> = true;

#endif // C++17

#if _GLIBCXX_USE_BUILTIN_TRAIT(__type_pack_element)
  template<size_t _Np, typename... _Types>
    struct _Nth_type
    { using type = __type_pack_element<_Np, _Types...>; };
#else
  template<size_t _Np, typename... _Types>
    struct _Nth_type
    { };

  template<typename _Tp0, typename... _Rest>
    struct _Nth_type<0, _Tp0, _Rest...>
    { using type = _Tp0; };

  template<typename _Tp0, typename _Tp1, typename... _Rest>
    struct _Nth_type<1, _Tp0, _Tp1, _Rest...>
    { using type = _Tp1; };

  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
    struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...>
    { using type = _Tp2; };

  template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2,
	   typename... _Rest>
#if __cpp_concepts
    requires (_Np >= 3)
#endif
    struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...>
    : _Nth_type<_Np - 3, _Rest...>
    { };

#if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
    struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
    { using type = _Tp0; };

  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
    struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...>
    { using type = _Tp1; };
#endif
#endif

#if __glibcxx_ranges
  namespace ranges::__detail
  {
    template<typename _Range>
      inline constexpr bool __is_subrange = false;
  } // namespace __detail
#endif

  // A class (and instance) which can be used in 'tie' when an element
  // of a tuple is not required.
  struct _Swallow_assign
  {
    template<class _Tp>
      constexpr const _Swallow_assign&
      operator=(const _Tp&) const noexcept
      { return *this; }
  };

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2773. Making std::ignore constexpr
  /** Used with `std::tie` to ignore an element of a tuple
   *
   * When using `std::tie` to assign the elements of a tuple to variables,
   * unwanted elements can be ignored by using `std::ignore`. For example:
   *
   * ```
   * int x, y;
   * std::tie(x, std::ignore, y) = std::make_tuple(1, 2, 3);
   * ```
   *
   * This assignment will perform `x=1; std::ignore=2; y=3;` which results
   * in the second element being ignored.
   *
   * @since C++11
   */
  _GLIBCXX17_INLINE constexpr _Swallow_assign ignore{};

#if __glibcxx_flat_map || __glibcxx_flat_set // >= C++23
  struct sorted_unique_t { explicit sorted_unique_t() = default; };
  inline constexpr sorted_unique_t sorted_unique{};

  struct sorted_equivalent_t { explicit sorted_equivalent_t() = default; };
  inline constexpr sorted_equivalent_t sorted_equivalent{};
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif // C++11
#endif /* _GLIBCXX_UTILITY_H */