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

   1 // The  -*- C++ -*- type traits classes for internal use in libstdc++
   2
   3 // Copyright (C) 2000-2018 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file bits/cpp_type_traits.h
  26  *  This is an internal header file, included by other library headers.
  27  *  Do not attempt to use it directly. @headername{ext/type_traits}
  28  */
  29
  30 // Written by Gabriel Dos Reis <dosreis@cmla.ens-cachan.fr>
  31
  32 #ifndef _CPP_TYPE_TRAITS_H
  33 #define _CPP_TYPE_TRAITS_H 1
  34
  35 #pragma GCC system_header
  36
  37 #include <bits/c++config.h>
  38
  39 //
  40 // This file provides some compile-time information about various types.
  41 // These representations were designed, on purpose, to be constant-expressions
  42 // and not types as found in <bits/type_traits.h>.  In particular, they
  43 // can be used in control structures and the optimizer hopefully will do
  44 // the obvious thing.
  45 //
  46 // Why integral expressions, and not functions nor types?
  47 // Firstly, these compile-time entities are used as template-arguments
  48 // so function return values won't work:  We need compile-time entities.
  49 // We're left with types and constant  integral expressions.
  50 // Secondly, from the point of view of ease of use, type-based compile-time
  51 // information is -not- *that* convenient.  On has to write lots of
  52 // overloaded functions and to hope that the compiler will select the right
  53 // one. As a net effect, the overall structure isn't very clear at first
  54 // glance.
  55 // Thirdly, partial ordering and overload resolution (of function templates)
  56 // is highly costly in terms of compiler-resource.  It is a Good Thing to
  57 // keep these resource consumption as least as possible.
  58 //
  59 // See valarray_array.h for a case use.
  60 //
  61 // -- Gaby (dosreis@cmla.ens-cachan.fr) 2000-03-06.
  62 //
  63 // Update 2005: types are also provided and <bits/type_traits.h> has been
  64 // removed.
  65 //
  66
  67 extern "C++" {
  68
  69 namespace std _GLIBCXX_VISIBILITY(default)
  70 {
  71 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  72
  73   struct __true_type { };
  74   struct __false_type { };
  75
  76   template<bool>
  77     struct __truth_type
  78     { typedef __false_type __type; };
  79
  80   template<>
  81     struct __truth_type<true>
  82     { typedef __true_type __type; };
  83
  84   // N.B. The conversions to bool are needed due to the issue
  85   // explained in c++/19404.
  86   template<class _Sp, class _Tp>
  87     struct __traitor
  88     {
  89       enum { __value = bool(_Sp::__value) || bool(_Tp::__value) };
  90       typedef typename __truth_type<__value>::__type __type;
  91     };
  92
  93   // Compare for equality of types.
  94   template<typename, typename>
  95     struct __are_same
  96     {
  97       enum { __value = 0 };
  98       typedef __false_type __type;
  99     };
 100
 101   template<typename _Tp>
 102     struct __are_same<_Tp, _Tp>
 103     {
 104       enum { __value = 1 };
 105       typedef __true_type __type;
 106     };
 107
 108   // Holds if the template-argument is a void type.
 109   template<typename _Tp>
 110     struct __is_void
 111     {
 112       enum { __value = 0 };
 113       typedef __false_type __type;
 114     };
 115
 116   template<>
 117     struct __is_void<void>
 118     {
 119       enum { __value = 1 };
 120       typedef __true_type __type;
 121     };
 122
 123   //
 124   // Integer types
 125   //
 126   template<typename _Tp>
 127     struct __is_integer
 128     {
 129       enum { __value = 0 };
 130       typedef __false_type __type;
 131     };
 132
 133   // Thirteen specializations (yes there are eleven standard integer
 134   // types; <em>long long</em> and <em>unsigned long long</em> are
 135   // supported as extensions).  Up to four target-specific __int<N>
 136   // types are supported as well.
 137   template<>
 138     struct __is_integer<bool>
 139     {
 140       enum { __value = 1 };
 141       typedef __true_type __type;
 142     };
 143
 144   template<>
 145     struct __is_integer<char>
 146     {
 147       enum { __value = 1 };
 148       typedef __true_type __type;
 149     };
 150
 151   template<>
 152     struct __is_integer<signed char>
 153     {
 154       enum { __value = 1 };
 155       typedef __true_type __type;
 156     };
 157
 158   template<>
 159     struct __is_integer<unsigned char>
 160     {
 161       enum { __value = 1 };
 162       typedef __true_type __type;
 163     };
 164
 165 # ifdef _GLIBCXX_USE_WCHAR_T
 166   template<>
 167     struct __is_integer<wchar_t>
 168     {
 169       enum { __value = 1 };
 170       typedef __true_type __type;
 171     };
 172 # endif
 173
 174 #if __cplusplus >= 201103L
 175   template<>
 176     struct __is_integer<char16_t>
 177     {
 178       enum { __value = 1 };
 179       typedef __true_type __type;
 180     };
 181
 182   template<>
 183     struct __is_integer<char32_t>
 184     {
 185       enum { __value = 1 };
 186       typedef __true_type __type;
 187     };
 188 #endif
 189
 190   template<>
 191     struct __is_integer<short>
 192     {
 193       enum { __value = 1 };
 194       typedef __true_type __type;
 195     };
 196
 197   template<>
 198     struct __is_integer<unsigned short>
 199     {
 200       enum { __value = 1 };
 201       typedef __true_type __type;
 202     };
 203
 204   template<>
 205     struct __is_integer<int>
 206     {
 207       enum { __value = 1 };
 208       typedef __true_type __type;
 209     };
 210
 211   template<>
 212     struct __is_integer<unsigned int>
 213     {
 214       enum { __value = 1 };
 215       typedef __true_type __type;
 216     };
 217
 218   template<>
 219     struct __is_integer<long>
 220     {
 221       enum { __value = 1 };
 222       typedef __true_type __type;
 223     };
 224
 225   template<>
 226     struct __is_integer<unsigned long>
 227     {
 228       enum { __value = 1 };
 229       typedef __true_type __type;
 230     };
 231
 232   template<>
 233     struct __is_integer<long long>
 234     {
 235       enum { __value = 1 };
 236       typedef __true_type __type;
 237     };
 238
 239   template<>
 240     struct __is_integer<unsigned long long>
 241     {
 242       enum { __value = 1 };
 243       typedef __true_type __type;
 244     };
 245
 246 #define __INT_N(TYPE)                   \
 247   template<>                            \
 248     struct __is_integer<TYPE>           \
 249     {                                   \
 250       enum { __value = 1 };             \
 251       typedef __true_type __type;       \
 252     };                                  \
 253   template<>                            \
 254     struct __is_integer<unsigned TYPE>  \
 255     {                                   \
 256       enum { __value = 1 };             \
 257       typedef __true_type __type;       \
 258     };
 259
 260 #ifdef __GLIBCXX_TYPE_INT_N_0
 261 __INT_N(__GLIBCXX_TYPE_INT_N_0)
 262 #endif
 263 #ifdef __GLIBCXX_TYPE_INT_N_1
 264 __INT_N(__GLIBCXX_TYPE_INT_N_1)
 265 #endif
 266 #ifdef __GLIBCXX_TYPE_INT_N_2
 267 __INT_N(__GLIBCXX_TYPE_INT_N_2)
 268 #endif
 269 #ifdef __GLIBCXX_TYPE_INT_N_3
 270 __INT_N(__GLIBCXX_TYPE_INT_N_3)
 271 #endif
 272
 273 #undef __INT_N
 274
 275   //
 276   // Floating point types
 277   //
 278   template<typename _Tp>
 279     struct __is_floating
 280     {
 281       enum { __value = 0 };
 282       typedef __false_type __type;
 283     };
 284
 285   // three specializations (float, double and 'long double')
 286   template<>
 287     struct __is_floating<float>
 288     {
 289       enum { __value = 1 };
 290       typedef __true_type __type;
 291     };
 292
 293   template<>
 294     struct __is_floating<double>
 295     {
 296       enum { __value = 1 };
 297       typedef __true_type __type;
 298     };
 299
 300   template<>
 301     struct __is_floating<long double>
 302     {
 303       enum { __value = 1 };
 304       typedef __true_type __type;
 305     };
 306
 307   //
 308   // Pointer types
 309   //
 310   template<typename _Tp>
 311     struct __is_pointer
 312     {
 313       enum { __value = 0 };
 314       typedef __false_type __type;
 315     };
 316
 317   template<typename _Tp>
 318     struct __is_pointer<_Tp*>
 319     {
 320       enum { __value = 1 };
 321       typedef __true_type __type;
 322     };
 323
 324   //
 325   // An arithmetic type is an integer type or a floating point type
 326   //
 327   template<typename _Tp>
 328     struct __is_arithmetic
 329     : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
 330     { };
 331
 332   //
 333   // A scalar type is an arithmetic type or a pointer type
 334   //
 335   template<typename _Tp>
 336     struct __is_scalar
 337     : public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> >
 338     { };
 339
 340   //
 341   // For use in std::copy and std::find overloads for streambuf iterators.
 342   //
 343   template<typename _Tp>
 344     struct __is_char
 345     {
 346       enum { __value = 0 };
 347       typedef __false_type __type;
 348     };
 349
 350   template<>
 351     struct __is_char<char>
 352     {
 353       enum { __value = 1 };
 354       typedef __true_type __type;
 355     };
 356
 357 #ifdef _GLIBCXX_USE_WCHAR_T
 358   template<>
 359     struct __is_char<wchar_t>
 360     {
 361       enum { __value = 1 };
 362       typedef __true_type __type;
 363     };
 364 #endif
 365
 366   template<typename _Tp>
 367     struct __is_byte
 368     {
 369       enum { __value = 0 };
 370       typedef __false_type __type;
 371     };
 372
 373   template<>
 374     struct __is_byte<char>
 375     {
 376       enum { __value = 1 };
 377       typedef __true_type __type;
 378     };
 379
 380   template<>
 381     struct __is_byte<signed char>
 382     {
 383       enum { __value = 1 };
 384       typedef __true_type __type;
 385     };
 386
 387   template<>
 388     struct __is_byte<unsigned char>
 389     {
 390       enum { __value = 1 };
 391       typedef __true_type __type;
 392     };
 393
 394   //
 395   // Move iterator type
 396   //
 397   template<typename _Tp>
 398     struct __is_move_iterator
 399     {
 400       enum { __value = 0 };
 401       typedef __false_type __type;
 402     };
 403
 404   // Fallback implementation of the function in bits/stl_iterator.h used to
 405   // remove the move_iterator wrapper.
 406   template<typename _Iterator>
 407     inline _Iterator
 408     __miter_base(_Iterator __it)
 409     { return __it; }
 410
 411 _GLIBCXX_END_NAMESPACE_VERSION
 412 } // namespace
 413 } // extern "C++"
 414
 415 #endif //_CPP_TYPE_TRAITS_H