1 files changed, 140 insertions, 0 deletions
diff --git a/dom/bindings/Nullable.h b/dom/bindings/Nullable.h
new file mode 100644
index 000000000..8d7d46905
--- /dev/null
+++ b/dom/bindings/Nullable.h
@@ -0,0 +1,140 @@
+/* -*- 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()
+  {}
+
+  MOZ_IMPLICIT Nullable(const decltype(nullptr)&)
+    : mValue()
+  {}
+
+  explicit Nullable(const T& aValue)
+    : mValue()
+  {
+    mValue.emplace(aValue);
+  }
+
+  MOZ_IMPLICIT 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 */