Filename: //usr//include/c++/10/bits/cpp_type_traits.h

// The -*- C++ -*- type traits classes for internal use in libstdc++ // Copyright (C) 2000-2020 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 _GLIBCXX_USE_WCHAR_T 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) \ template<> \ struct __is_integer<TYPE> \ { \ enum { __value = 1 }; \ typedef __true_type __type; \ }; \ 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 _GLIBCXX_USE_WCHAR_T 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 narrow character types (and std::byte). template<typename _Tp, bool _TreatAsBytes = __is_byte<_Tp>::__value> 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 // 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

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