uspace/lib/cpp/include/__bits/aux.hpp

   1 /*
   2  * Copyright (c) 2018 Jaroslav Jindrak
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  *
   9  * - Redistributions of source code must retain the above copyright
  10  *   notice, this list of conditions and the following disclaimer.
  11  * - Redistributions in binary form must reproduce the above copyright
  12  *   notice, this list of conditions and the following disclaimer in the
  13  *   documentation and/or other materials provided with the distribution.
  14  * - The name of the author may not be used to endorse or promote products
  15  *   derived from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef LIBCPP_BITS_AUX
  30 #define LIBCPP_BITS_AUX
  31
  32 namespace std
  33 {
  34     /**
  35      * 20.10.3, helper class:
  36      */
  37
  38     template<class T, T v>
  39     struct integral_constant
  40     {
  41         static constexpr T value = v;
  42
  43         using value_type = T;
  44         using type       = integral_constant<T, v>;
  45
  46         constexpr operator value_type() const noexcept
  47         {
  48             return value;
  49         }
  50
  51         constexpr value_type operator()() const noexcept
  52         {
  53             return value;
  54         }
  55     };
  56
  57     using true_type = integral_constant<bool, true>;
  58     using false_type = integral_constant<bool, false>;
  59 }
  60
  61 namespace std::aux
  62 {
  63     /**
  64      * Two very handy templates, this allows us
  65      * to easily follow the T::type and T::value
  66      * convention by simply inheriting from specific
  67      * instantiations of these templates.
  68      * Examples:
  69      *  1) We need a struct with int typedef'd to type:
  70      *
  71      *      stuct has_type_int: aux::type<int> {};
  72      *      typename has_type_int::type x = 1; // x is of type int
  73      *
  74      *  2) We need a struct with static size_t member called value:
  75      *
  76      *      struct has_value_size_t: aux::value<size_t, 1u> {};
  77      *      std::printf("%u\n", has_value_size_t::value); // prints "1\n"
  78      */
  79
  80     template<class T>
  81     struct type_is
  82     {
  83         using type = T;
  84     };
  85
  86     // For compatibility with integral_constant.
  87     template<class T, T v>
  88     using value_is = std::integral_constant<T, v>;
  89 }
  90
  91 #endif