gecko-dev/dom/bindings/UnionMember.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* A class for holding the members of a union. */

#ifndef mozilla_dom_UnionMember_h
#define mozilla_dom_UnionMember_h

#include "mozilla/Alignment.h"
#include "mozilla/Attributes.h"
#include <utility>

namespace mozilla::dom {

// The union type has an enum to keep track of which of its UnionMembers has
// been constructed.
template <class T>
class UnionMember {
  AlignedStorage2<T> mStorage;

  // Copy construction can't be supported because C++ requires that any enclosed
  // T be initialized in a way C++ knows about -- that is, by |new| or similar.
  UnionMember(const UnionMember&) = delete;

 public:
  UnionMember() = default;
  ~UnionMember() = default;

  template <typename... Args>
  T& SetValue(Args&&... args) {
    new (mStorage.addr()) T(std::forward<Args>(args)...);
    return *mStorage.addr();
  }

  T& Value() { return *mStorage.addr(); }
  const T& Value() const { return *mStorage.addr(); }
  void Destroy() { mStorage.addr()->~T(); }
} MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS;

}  // namespace mozilla::dom

#endif  // mozilla_dom_UnionMember_h