ceph/src/common/backport14.h

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3 /*
   4  * Ceph - scalable distributed file system
   5  *
   6  * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
   7  *
   8  * This is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License version 2.1, as published by the Free Software
  11  * Foundation.  See file COPYING.
  12  *
  13  */
  14
  15 #include <memory>
  16 #include <type_traits>
  17
  18 #ifndef CEPH_COMMON_BACKPORT14_H
  19 #define CEPH_COMMON_BACKPORT14_H
  20
  21 // Library code from C++14 that can be implemented in C++11.
  22
  23 namespace ceph {
  24 template<typename T>
  25 using remove_extent_t = typename std::remove_extent<T>::type;
  26 template<typename T>
  27 using remove_reference_t = typename std::remove_reference<T>::type;
  28 template<typename T>
  29 using result_of_t = typename std::result_of<T>::type;
  30 template<typename T>
  31 using decay_t = typename std::decay<T>::type;
  32
  33 namespace _backport14 {
  34 template<typename T>
  35 struct uniquity {
  36   using datum = std::unique_ptr<T>;
  37 };
  38
  39 template<typename T>
  40 struct uniquity<T[]> {
  41   using array = std::unique_ptr<T[]>;
  42 };
  43
  44 template<typename T, std::size_t N>
  45 struct uniquity<T[N]> {
  46   using verboten = void;
  47 };
  48
  49 template<typename T, typename... Args>
  50 inline typename uniquity<T>::datum make_unique(Args&&... args) {
  51   return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
  52 }
  53
  54 template<typename T>
  55 inline typename uniquity<T>::array make_unique(std::size_t n) {
  56   return std::unique_ptr<T>(new remove_extent_t<T>[n]());
  57 }
  58
  59 template<typename T, class... Args>
  60 typename uniquity<T>::verboten
  61 make_unique(Args&&...) = delete;
  62
  63 // The constexpr variant of std::max().
  64 template<class T>
  65 constexpr const T& max(const T& a, const T& b) {
  66   return a < b ? b : a;
  67 }
  68 } // namespace _backport14
  69
  70 namespace _backport17 {
  71 template <class C>
  72 constexpr auto size(const C& c) -> decltype(c.size()) {
  73   return c.size();
  74 }
  75
  76 template <typename T, std::size_t N>
  77 constexpr std::size_t size(const T (&array)[N]) noexcept {
  78   return N;
  79 }
  80
  81 /// http://en.cppreference.com/w/cpp/utility/functional/not_fn
  82 // this implementation uses c++14's result_of_t (above) instead of the c++17
  83 // invoke_result_t, and so may not behave correctly when SFINAE is required
  84 template <typename F>
  85 class not_fn_result {
  86   using DecayF = decay_t<F>;
  87   DecayF fn;
  88  public:
  89   explicit not_fn_result(F&& f) : fn(std::forward<F>(f)) {}
  90   not_fn_result(not_fn_result&& f) = default;
  91   not_fn_result(const not_fn_result& f) = default;
  92
  93   template<class... Args>
  94   auto operator()(Args&&... args) &
  95   -> decltype(!std::declval<result_of_t<DecayF&(Args...)>>()) {
  96     return !fn(std::forward<Args>(args)...);
  97   }
  98   template<class... Args>
  99   auto operator()(Args&&... args) const&
 100   -> decltype(!std::declval<result_of_t<DecayF const&(Args...)>>()) {
 101     return !fn(std::forward<Args>(args)...);
 102   }
 103
 104   template<class... Args>
 105   auto operator()(Args&&... args) &&
 106   -> decltype(!std::declval<result_of_t<DecayF(Args...)>>()) {
 107     return !std::move(fn)(std::forward<Args>(args)...);
 108   }
 109   template<class... Args>
 110   auto operator()(Args&&... args) const&&
 111   -> decltype(!std::declval<result_of_t<DecayF const(Args...)>>()) {
 112     return !std::move(fn)(std::forward<Args>(args)...);
 113   }
 114 };
 115
 116 template <typename F>
 117 not_fn_result<F> not_fn(F&& fn) {
 118   return not_fn_result<F>(std::forward<F>(fn));
 119 }
 120
 121 } // namespace _backport17
 122 using _backport14::make_unique;
 123 using _backport17::size;
 124 using _backport14::max;
 125 using _backport17::not_fn;
 126 } // namespace ceph
 127
 128 #endif // CEPH_COMMON_BACKPORT14_H