runtime/DenseMapExtras.h

   1 /*
   2  * Copyright (c) 2019 Apple Inc.  All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #ifndef DENSEMAPEXTRAS_H
  25 #define DENSEMAPEXTRAS_H
  26
  27 #include "llvm-DenseMap.h"
  28 #include "llvm-DenseSet.h"
  29
  30 namespace objc {
  31
  32 // We cannot use a C++ static initializer to initialize certain globals because
  33 // libc calls us before our C++ initializers run. We also don't want a global
  34 // pointer to some globals because of the extra indirection.
  35 //
  36 // ExplicitInit / LazyInit wrap doing it the hard way.
  37 template <typename Type>
  38 class ExplicitInit {
  39     alignas(Type) uint8_t _storage[sizeof(Type)];
  40
  41 public:
  42     template <typename... Ts>
  43     void init(Ts &&... Args) {
  44         new (_storage) Type(std::forward<Ts>(Args)...);
  45     }
  46
  47     Type &get() {
  48         return *reinterpret_cast<Type *>(_storage);
  49     }
  50 };
  51
  52 template <typename Type>
  53 class LazyInit {
  54     alignas(Type) uint8_t _storage[sizeof(Type)];
  55     bool _didInit;
  56
  57 public:
  58     template <typename... Ts>
  59     Type *get(bool allowCreate, Ts &&... Args) {
  60         if (!_didInit) {
  61             if (!allowCreate) {
  62                 return nullptr;
  63             }
  64             new (_storage) Type(std::forward<Ts>(Args)...);
  65             _didInit = true;
  66         }
  67         return reinterpret_cast<Type *>(_storage);
  68     }
  69 };
  70
  71 // Convenience class for Dense Maps & Sets
  72 template <typename Key, typename Value>
  73 class ExplicitInitDenseMap : public ExplicitInit<DenseMap<Key, Value>> { };
  74
  75 template <typename Key, typename Value>
  76 class LazyInitDenseMap : public LazyInit<DenseMap<Key, Value>> { };
  77
  78 template <typename Value>
  79 class ExplicitInitDenseSet : public ExplicitInit<DenseSet<Value>> { };
  80
  81 template <typename Value>
  82 class LazyInitDenseSet : public LazyInit<DenseSet<Value>> { };
  83
  84 } // namespace objc
  85
  86 #endif /* DENSEMAPEXTRAS_H */