dom/bindings/UnionMember.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* A class for holding the members of a union. */
   8
   9 #ifndef mozilla_dom_UnionMember_h
  10 #define mozilla_dom_UnionMember_h
  11
  12 #include "mozilla/Alignment.h"
  13 #include "mozilla/Attributes.h"
  14 #include <utility>
  15
  16 namespace mozilla::dom {
  17
  18 // The union type has an enum to keep track of which of its UnionMembers has
  19 // been constructed.
  20 template <class T>
  21 class UnionMember {
  22   AlignedStorage2<T> mStorage;
  23
  24   // Copy construction can't be supported because C++ requires that any enclosed
  25   // T be initialized in a way C++ knows about -- that is, by |new| or similar.
  26   UnionMember(const UnionMember&) = delete;
  27
  28  public:
  29   UnionMember() = default;
  30   ~UnionMember() = default;
  31
  32   template <typename... Args>
  33   T& SetValue(Args&&... args) {
  34     new (mStorage.addr()) T(std::forward<Args>(args)...);
  35     return *mStorage.addr();
  36   }
  37
  38   T& Value() { return *mStorage.addr(); }
  39   const T& Value() const { return *mStorage.addr(); }
  40   void Destroy() { mStorage.addr()->~T(); }
  41 } MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS;
  42
  43 }  // namespace mozilla::dom
  44
  45 #endif  // mozilla_dom_UnionMember_h