cpp_type_traits.h
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// The -*- C++ -*- type traits classes for internal use in libstdc++
// Copyright (C) 2000-2022 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/cpp_type_traits.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{ext/type_traits}
*/
// Written by Gabriel Dos Reis <dosreis@cmla.ens-cachan.fr>
#ifndef _CPP_TYPE_TRAITS_H
#define _CPP_TYPE_TRAITS_H 1
#pragma GCC system_header
#include <bits/c++config.h>
//
// This file provides some compile-time information about various types.
// These representations were designed, on purpose, to be constant-expressions
// and not types as found in <bits/type_traits.h>. In particular, they
// can be used in control structures and the optimizer hopefully will do
// the obvious thing.
//
// Why integral expressions, and not functions nor types?
// Firstly, these compile-time entities are used as template-arguments
// so function return values won't work: We need compile-time entities.
// We're left with types and constant integral expressions.
// Secondly, from the point of view of ease of use, type-based compile-time
// information is -not- *that* convenient. One has to write lots of
// overloaded functions and to hope that the compiler will select the right
// one. As a net effect, the overall structure isn't very clear at first
// glance.
// Thirdly, partial ordering and overload resolution (of function templates)
// is highly costly in terms of compiler-resource. It is a Good Thing to
// keep these resource consumption as least as possible.
//
// See valarray_array.h for a case use.
//
// -- Gaby (dosreis@cmla.ens-cachan.fr) 2000-03-06.
//
// Update 2005: types are also provided and <bits/type_traits.h> has been
// removed.
//
extern "C++" {
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
struct __true_type { };
struct __false_type { };
template<bool>
struct __truth_type
{ typedef __false_type __type; };
template<>
struct __truth_type<true>
{ typedef __true_type __type; };
// N.B. The conversions to bool are needed due to the issue
// explained in c++/19404.
template<class _Sp, class _Tp>
struct __traitor
{
enum { __value = bool(_Sp::__value) || bool(_Tp::__value) };
typedef typename __truth_type<__value>::__type __type;
};
// Compare for equality of types.
template<typename, typename>
struct __are_same
{
enum { __value = 0 };
typedef __false_type __type;
};
template<typename _Tp>
struct __are_same<_Tp, _Tp>
{
enum { __value = 1 };
typedef __true_type __type;
};
// Holds if the template-argument is a void type.
template<typename _Tp>
struct __is_void
{
enum { __value = 0 };
typedef __false_type __type;
};
template<>
struct __is_void<void>
{
enum { __value = 1 };
typedef __true_type __type;
};
//
// Integer types
//
template<typename _Tp>
struct __is_integer
{
enum { __value = 0 };
typedef __false_type __type;
};
// Thirteen specializations (yes there are eleven standard integer
// types; <em>long long</em> and <em>unsigned long long</em> are
// supported as extensions). Up to four target-specific __int<N>
// types are supported as well.
template<>
struct __is_integer<bool>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<char>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<signed char>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<unsigned char>
{
enum { __value = 1 };
typedef __true_type __type;
};
# ifdef __WCHAR_TYPE__
template<>
struct __is_integer<wchar_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
# endif
#ifdef _GLIBCXX_USE_CHAR8_T
template<>
struct __is_integer<char8_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
#endif
#if __cplusplus >= 201103L
template<>
struct __is_integer<char16_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<char32_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
#endif
template<>
struct __is_integer<short>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<unsigned short>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<int>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<unsigned int>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<long>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<unsigned long>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<long long>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_integer<unsigned long long>
{
enum { __value = 1 };
typedef __true_type __type;
};
#define __INT_N(TYPE) \
__extension__ \
template<> \
struct __is_integer<TYPE> \
{ \
enum { __value = 1 }; \
typedef __true_type __type; \
}; \
__extension__ \
template<> \
struct __is_integer<unsigned TYPE> \
{ \
enum { __value = 1 }; \
typedef __true_type __type; \
};
#ifdef __GLIBCXX_TYPE_INT_N_0
__INT_N(__GLIBCXX_TYPE_INT_N_0)
#endif
#ifdef __GLIBCXX_TYPE_INT_N_1
__INT_N(__GLIBCXX_TYPE_INT_N_1)
#endif
#ifdef __GLIBCXX_TYPE_INT_N_2
__INT_N(__GLIBCXX_TYPE_INT_N_2)
#endif
#ifdef __GLIBCXX_TYPE_INT_N_3
__INT_N(__GLIBCXX_TYPE_INT_N_3)
#endif
#undef __INT_N
//
// Floating point types
//
template<typename _Tp>
struct __is_floating
{
enum { __value = 0 };
typedef __false_type __type;
};
// three specializations (float, double and 'long double')
template<>
struct __is_floating<float>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_floating<double>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_floating<long double>
{
enum { __value = 1 };
typedef __true_type __type;
};
//
// Pointer types
//
template<typename _Tp>
struct __is_pointer
{
enum { __value = 0 };
typedef __false_type __type;
};
template<typename _Tp>
struct __is_pointer<_Tp*>
{
enum { __value = 1 };
typedef __true_type __type;
};
//
// An arithmetic type is an integer type or a floating point type
//
template<typename _Tp>
struct __is_arithmetic
: public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
{ };
//
// A scalar type is an arithmetic type or a pointer type
//
template<typename _Tp>
struct __is_scalar
: public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> >
{ };
//
// For use in std::copy and std::find overloads for streambuf iterators.
//
template<typename _Tp>
struct __is_char
{
enum { __value = 0 };
typedef __false_type __type;
};
template<>
struct __is_char<char>
{
enum { __value = 1 };
typedef __true_type __type;
};
#ifdef __WCHAR_TYPE__
template<>
struct __is_char<wchar_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
#endif
template<typename _Tp>
struct __is_byte
{
enum { __value = 0 };
typedef __false_type __type;
};
template<>
struct __is_byte<char>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_byte<signed char>
{
enum { __value = 1 };
typedef __true_type __type;
};
template<>
struct __is_byte<unsigned char>
{
enum { __value = 1 };
typedef __true_type __type;
};
#if __cplusplus >= 201703L
enum class byte : unsigned char;
template<>
struct __is_byte<byte>
{
enum { __value = 1 };
typedef __true_type __type;
};
#endif // C++17
#ifdef _GLIBCXX_USE_CHAR8_T
template<>
struct __is_byte<char8_t>
{
enum { __value = 1 };
typedef __true_type __type;
};
#endif
template<typename> struct iterator_traits;
// A type that is safe for use with memcpy, memmove, memcmp etc.
template<typename _Tp>
struct __is_nonvolatile_trivially_copyable
{
enum { __value = __is_trivially_copyable(_Tp) };
};
// Cannot use memcpy/memmove/memcmp on volatile types even if they are
// trivially copyable, so ensure __memcpyable<volatile int*, volatile int*>
// and similar will be false.
template<typename _Tp>
struct __is_nonvolatile_trivially_copyable<volatile _Tp>
{
enum { __value = 0 };
};
// Whether two iterator types can be used with memcpy/memmove.
template<typename _OutputIter, typename _InputIter>
struct __memcpyable
{
enum { __value = 0 };
};
template<typename _Tp>
struct __memcpyable<_Tp*, _Tp*>
: __is_nonvolatile_trivially_copyable<_Tp>
{ };
template<typename _Tp>
struct __memcpyable<_Tp*, const _Tp*>
: __is_nonvolatile_trivially_copyable<_Tp>
{ };
// Whether two iterator types can be used with memcmp.
// This trait only says it's well-formed to use memcmp, not that it
// gives the right answer for a given algorithm. So for example, std::equal
// needs to add additional checks that the types are integers or pointers,
// because other trivially copyable types can overload operator==.
template<typename _Iter1, typename _Iter2>
struct __memcmpable
{
enum { __value = 0 };
};
// OK to use memcmp with pointers to trivially copyable types.
template<typename _Tp>
struct __memcmpable<_Tp*, _Tp*>
: __is_nonvolatile_trivially_copyable<_Tp>
{ };
template<typename _Tp>
struct __memcmpable<const _Tp*, _Tp*>
: __is_nonvolatile_trivially_copyable<_Tp>
{ };
template<typename _Tp>
struct __memcmpable<_Tp*, const _Tp*>
: __is_nonvolatile_trivially_copyable<_Tp>
{ };
// Whether memcmp can be used to determine ordering for a type
// e.g. in std::lexicographical_compare or three-way comparisons.
// True for unsigned integer-like types where comparing each byte in turn
// as an unsigned char yields the right result. This is true for all
// unsigned integers on big endian targets, but only unsigned narrow
// character types (and std::byte) on little endian targets.
template<typename _Tp, bool _TreatAsBytes =
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
__is_integer<_Tp>::__value
#else
__is_byte<_Tp>::__value
#endif
>
struct __is_memcmp_ordered
{
static const bool __value = _Tp(-1) > _Tp(1); // is unsigned
};
template<typename _Tp>
struct __is_memcmp_ordered<_Tp, false>
{
static const bool __value = false;
};
// Whether two types can be compared using memcmp.
template<typename _Tp, typename _Up, bool = sizeof(_Tp) == sizeof(_Up)>
struct __is_memcmp_ordered_with
{
static const bool __value = __is_memcmp_ordered<_Tp>::__value
&& __is_memcmp_ordered<_Up>::__value;
};
template<typename _Tp, typename _Up>
struct __is_memcmp_ordered_with<_Tp, _Up, false>
{
static const bool __value = false;
};
#if __cplusplus >= 201703L
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
// std::byte is not an integer, but it can be compared using memcmp.
template<>
struct __is_memcmp_ordered<std::byte, false>
{ static constexpr bool __value = true; };
#endif
// std::byte can only be compared to itself, not to other types.
template<>
struct __is_memcmp_ordered_with<std::byte, std::byte, true>
{ static constexpr bool __value = true; };
template<typename _Tp, bool _SameSize>
struct __is_memcmp_ordered_with<_Tp, std::byte, _SameSize>
{ static constexpr bool __value = false; };
template<typename _Up, bool _SameSize>
struct __is_memcmp_ordered_with<std::byte, _Up, _SameSize>
{ static constexpr bool __value = false; };
#endif
//
// Move iterator type
//
template<typename _Tp>
struct __is_move_iterator
{
enum { __value = 0 };
typedef __false_type __type;
};
// Fallback implementation of the function in bits/stl_iterator.h used to
// remove the move_iterator wrapper.
template<typename _Iterator>
_GLIBCXX20_CONSTEXPR
inline _Iterator
__miter_base(_Iterator __it)
{ return __it; }
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
} // extern "C++"
#endif //_CPP_TYPE_TRAITS_H
c++config.h
std
ISO C++ entities toplevel namespace is std.
std::byte
byte
std::byte
Definition: cstddef:69