ceph/src/boost/boost/beast/core/detail/empty_base_optimization.hpp

   1 //
   2 // Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
   3 //
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7 // Official repository: https://github.com/boostorg/beast
   8 //
   9
  10 #ifndef BOOST_BEAST_DETAIL_EMPTY_BASE_OPTIMIZATION_HPP
  11 #define BOOST_BEAST_DETAIL_EMPTY_BASE_OPTIMIZATION_HPP
  12
  13 #include <boost/type_traits/is_final.hpp>
  14 #include <type_traits>
  15 #include <utility>
  16
  17 namespace boost {
  18 namespace beast {
  19 namespace detail {
  20
  21 template<class T>
  22 struct is_empty_base_optimization_derived
  23     : std::integral_constant<bool,
  24         std::is_empty<T>::value &&
  25         ! boost::is_final<T>::value>
  26 {
  27 };
  28
  29 template<class T, int UniqueID = 0,
  30     bool isDerived =
  31         is_empty_base_optimization_derived<T>::value>
  32 class empty_base_optimization : private T
  33 {
  34 public:
  35     empty_base_optimization() = default;
  36     empty_base_optimization(empty_base_optimization&&) = default;
  37     empty_base_optimization(empty_base_optimization const&) = default;
  38     empty_base_optimization& operator=(empty_base_optimization&&) = default;
  39     empty_base_optimization& operator=(empty_base_optimization const&) = default;
  40
  41     template<class Arg1, class... ArgN>
  42     explicit
  43     empty_base_optimization(Arg1&& arg1, ArgN&&... argn)
  44         : T(std::forward<Arg1>(arg1),
  45             std::forward<ArgN>(argn)...)
  46     {
  47     }
  48
  49     T& member() noexcept
  50     {
  51         return *this;
  52     }
  53
  54     T const& member() const noexcept
  55     {
  56         return *this;
  57     }
  58 };
  59
  60 //------------------------------------------------------------------------------
  61
  62 template<
  63     class T,
  64     int UniqueID
  65 >
  66 class empty_base_optimization <T, UniqueID, false>
  67 {
  68     T t_;
  69
  70 public:
  71     empty_base_optimization() = default;
  72     empty_base_optimization(empty_base_optimization&&) = default;
  73     empty_base_optimization(empty_base_optimization const&) = default;
  74     empty_base_optimization& operator=(empty_base_optimization&&) = default;
  75     empty_base_optimization& operator=(empty_base_optimization const&) = default;
  76
  77     template<class Arg1, class... ArgN>
  78     explicit
  79     empty_base_optimization(Arg1&& arg1, ArgN&&... argn)
  80         : t_(std::forward<Arg1>(arg1),
  81             std::forward<ArgN>(argn)...)
  82     {
  83     }
  84
  85     T& member() noexcept
  86     {
  87         return t_;
  88     }
  89
  90     T const& member() const noexcept
  91     {
  92         return t_;
  93     }
  94 };
  95
  96 } // detail
  97 } // beast
  98 } // boost
  99
 100 #endif