dom/bindings/Nullable.h
author Bob Owen <bobowencode@gmail.com>
Tue, 05 Jan 2016 10:08:57 +0000
changeset 278418 d765b7934fae4c1389ec4d860988a21437aed075
parent 263747 64821648efddfd3507c214b20d5126fa7b4c6fa9
child 282388 e22b3043887ed36bf2c634c2924a7c8d39d226b1
permissions -rw-r--r--
Bug 1156742 Part 7: Refactor nsDeviceContext.cpp to use printing surface for size and nsIDeviceContextSpec for DPI and scale. r=roc These changes are to make using an off screen surface behind our DrawTarget in the child easier. It still creates the real printing surface for some of the calculations, removing this will be required for future tightening of the sandbox.

/* -*- 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/. */

#ifndef mozilla_dom_Nullable_h
#define mozilla_dom_Nullable_h

#include "mozilla/Assertions.h"
#include "nsTArrayForwardDeclare.h"
#include "mozilla/Move.h"
#include "mozilla/Maybe.h"

class nsCycleCollectionTraversalCallback;

namespace mozilla {
namespace dom {

// Support for nullable types
template <typename T>
struct Nullable
{
private:
  Maybe<T> mValue;

public:
  Nullable()
    : mValue()
  {}

  explicit Nullable(const T& aValue)
    : mValue()
  {
    mValue.emplace(aValue);
  }

  explicit Nullable(T&& aValue)
    : mValue()
  {
    mValue.emplace(mozilla::Move(aValue));
  }

  Nullable(Nullable<T>&& aOther)
    : mValue(mozilla::Move(aOther.mValue))
  {}

  Nullable(const Nullable<T>& aOther)
    : mValue(aOther.mValue)
  {}

  void operator=(const Nullable<T>& aOther)
  {
    mValue = aOther.mValue;
  }

  void SetValue(const T& aArgs)
  {
    mValue.reset();
    mValue.emplace(aArgs);
  }

  void SetValue(T&& aArgs)
  {
    mValue.reset();
    mValue.emplace(mozilla::Move(aArgs));
  }

  // For cases when |T| is some type with nontrivial copy behavior, we may want
  // to get a reference to our internal copy of T and work with it directly
  // instead of relying on the copying version of SetValue().
  T& SetValue() {
    if (mValue.isNothing()) {
      mValue.emplace();
    }
    return mValue.ref();
  }

  void SetNull() {
    mValue.reset();
  }

  const T& Value() const {
    return mValue.ref();
  }

  T& Value() {
    return mValue.ref();
  }

  bool IsNull() const {
    return mValue.isNothing();
  }

  bool Equals(const Nullable<T>& aOtherNullable) const
  {
    return mValue == aOtherNullable.mValue;
  }

  bool operator==(const Nullable<T>& aOtherNullable) const
  {
    return Equals(aOtherNullable);
  }

  bool operator!=(const Nullable<T>& aOtherNullable) const
  {
    return !Equals(aOtherNullable);
  }
};


template<typename T>
void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                            Nullable<T>& aNullable,
                            const char* aName,
                            uint32_t aFlags = 0)
{
  if (!aNullable.IsNull()) {
    ImplCycleCollectionTraverse(aCallback, aNullable.Value(), aName, aFlags);
  }
}

template<typename T>
void
ImplCycleCollectionUnlink(Nullable<T>& aNullable)
{
  if (!aNullable.IsNull()) {
    ImplCycleCollectionUnlink(aNullable.Value());
  }
}

} // namespace dom
} // namespace mozilla

#endif /* mozilla_dom_Nullable_h */