ceph/src/arrow/cpp/src/arrow/util/type_traits.h

   1 // Licensed to the Apache Software Foundation (ASF) under one
   2 // or more contributor license agreements.  See the NOTICE file
   3 // distributed with this work for additional information
   4 // regarding copyright ownership.  The ASF licenses this file
   5 // to you under the Apache License, Version 2.0 (the
   6 // "License"); you may not use this file except in compliance
   7 // with the License.  You may obtain a copy of the License at
   8 //
   9 //   http://www.apache.org/licenses/LICENSE-2.0
  10 //
  11 // Unless required by applicable law or agreed to in writing,
  12 // software distributed under the License is distributed on an
  13 // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14 // KIND, either express or implied.  See the License for the
  15 // specific language governing permissions and limitations
  16 // under the License.
  17
  18 #pragma once
  19
  20 #include <cstdint>
  21 #include <type_traits>
  22
  23 namespace arrow {
  24 namespace internal {
  25
  26 /// \brief Metafunction to allow checking if a type matches any of another set of types
  27 template <typename...>
  28 struct IsOneOf : std::false_type {};  /// Base case: nothing has matched
  29
  30 template <typename T, typename U, typename... Args>
  31 struct IsOneOf<T, U, Args...> {
  32   /// Recursive case: T == U or T matches any other types provided (not including U).
  33   static constexpr bool value = std::is_same<T, U>::value || IsOneOf<T, Args...>::value;
  34 };
  35
  36 /// \brief Shorthand for using IsOneOf + std::enable_if
  37 template <typename T, typename... Args>
  38 using EnableIfIsOneOf = typename std::enable_if<IsOneOf<T, Args...>::value, T>::type;
  39
  40 /// \brief is_null_pointer from C++17
  41 template <typename T>
  42 struct is_null_pointer : std::is_same<std::nullptr_t, typename std::remove_cv<T>::type> {
  43 };
  44
  45 #ifdef __GLIBCXX__
  46
  47 // A aligned_union backport, because old libstdc++ versions don't include it.
  48
  49 constexpr std::size_t max_size(std::size_t a, std::size_t b) { return (a > b) ? a : b; }
  50
  51 template <typename...>
  52 struct max_size_traits;
  53
  54 template <typename H, typename... T>
  55 struct max_size_traits<H, T...> {
  56   static constexpr std::size_t max_sizeof() {
  57     return max_size(sizeof(H), max_size_traits<T...>::max_sizeof());
  58   }
  59   static constexpr std::size_t max_alignof() {
  60     return max_size(alignof(H), max_size_traits<T...>::max_alignof());
  61   }
  62 };
  63
  64 template <>
  65 struct max_size_traits<> {
  66   static constexpr std::size_t max_sizeof() { return 0; }
  67   static constexpr std::size_t max_alignof() { return 0; }
  68 };
  69
  70 template <std::size_t Len, typename... T>
  71 struct aligned_union {
  72   static constexpr std::size_t alignment_value = max_size_traits<T...>::max_alignof();
  73   static constexpr std::size_t size_value =
  74       max_size(Len, max_size_traits<T...>::max_sizeof());
  75   using type = typename std::aligned_storage<size_value, alignment_value>::type;
  76 };
  77
  78 #else
  79
  80 template <std::size_t Len, typename... T>
  81 using aligned_union = std::aligned_union<Len, T...>;
  82
  83 #endif
  84
  85 }  // namespace internal
  86 }  // namespace arrow