1 files changed, 198 insertions, 0 deletions
diff --git a/xpcom/base/OwningNonNull.h b/xpcom/base/OwningNonNull.h
new file mode 100644
index 000000000..b72a250c4
--- /dev/null
+++ b/xpcom/base/OwningNonNull.h
@@ -0,0 +1,198 @@
+/* -*- 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 non-null strong pointers to reference-counted objects. */
+
+#ifndef mozilla_OwningNonNull_h
+#define mozilla_OwningNonNull_h
+
+#include "nsAutoPtr.h"
+#include "nsCycleCollectionNoteChild.h"
+
+namespace mozilla {
+
+template<class T>
+class OwningNonNull
+{
+public:
+  OwningNonNull() {}
+
+  MOZ_IMPLICIT OwningNonNull(T& aValue)
+  {
+    init(&aValue);
+  }
+
+  template<class U>
+  MOZ_IMPLICIT OwningNonNull(already_AddRefed<U>&& aValue)
+  {
+    init(aValue);
+  }
+
+  template<class U>
+  MOZ_IMPLICIT OwningNonNull(const OwningNonNull<U>& aValue)
+  {
+    init(aValue);
+  }
+
+  // This is no worse than get() in terms of const handling.
+  operator T&() const
+  {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
+    return *mPtr;
+  }
+
+  operator T*() const
+  {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
+    return mPtr;
+  }
+
+  // Conversion to bool is always true, so delete to catch errors
+  explicit operator bool() const = delete;
+
+  T*
+  operator->() const
+  {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr, "OwningNonNull<T> was set to null");
+    return mPtr;
+  }
+
+  OwningNonNull<T>&
+  operator=(T* aValue)
+  {
+    init(aValue);
+    return *this;
+  }
+
+  OwningNonNull<T>&
+  operator=(T& aValue)
+  {
+    init(&aValue);
+    return *this;
+  }
+
+  template<class U>
+  OwningNonNull<T>&
+  operator=(already_AddRefed<U>&& aValue)
+  {
+    init(aValue);
+    return *this;
+  }
+
+  template<class U>
+  OwningNonNull<T>&
+  operator=(const OwningNonNull<U>& aValue)
+  {
+    init(aValue);
+    return *this;
+  }
+
+  // Don't allow assigning nullptr, it makes no sense
+  void operator=(decltype(nullptr)) = delete;
+
+  already_AddRefed<T> forget()
+  {
+#ifdef DEBUG
+    mInited = false;
+#endif
+    return mPtr.forget();
+  }
+
+  template<class U>
+  void
+  forget(U** aOther)
+  {
+#ifdef DEBUG
+    mInited = false;
+#endif
+    mPtr.forget(aOther);
+  }
+
+  // Make us work with smart pointer helpers that expect a get().
+  T* get() const
+  {
+    MOZ_ASSERT(mInited);
+    MOZ_ASSERT(mPtr);
+    return mPtr;
+  }
+
+  template<typename U>
+  void swap(U& aOther)
+  {
+    mPtr.swap(aOther);
+#ifdef DEBUG
+    mInited = mPtr;
+#endif
+  }
+
+  // We have some consumers who want to check whether we're inited in non-debug
+  // builds as well.  Luckily, we have the invariant that we're inited precisely
+  // when mPtr is non-null.
+  bool isInitialized() const
+  {
+    MOZ_ASSERT(!!mPtr == mInited, "mInited out of sync with mPtr?");
+    return mPtr;
+  }
+
+protected:
+  template<typename U>
+  void init(U&& aValue)
+  {
+    mPtr = aValue;
+    MOZ_ASSERT(mPtr);
+#ifdef DEBUG
+    mInited = true;
+#endif
+  }
+
+  RefPtr<T> mPtr;
+#ifdef DEBUG
+  bool mInited = false;
+#endif
+};
+
+template <typename T>
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            OwningNonNull<T>& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0)
+{
+  CycleCollectionNoteChild(aCallback, aField.get(), aName, aFlags);
+}
+
+} // namespace mozilla
+
+// Declared in nsCOMPtr.h
+template<class T> template<class U>
+nsCOMPtr<T>::nsCOMPtr(const mozilla::OwningNonNull<U>& aOther)
+  : nsCOMPtr(aOther.get())
+{}
+
+template<class T> template<class U>
+nsCOMPtr<T>&
+nsCOMPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther)
+{
+  return operator=(aOther.get());
+}
+
+// Declared in mozilla/RefPtr.h
+template<class T> template<class U>
+RefPtr<T>::RefPtr(const mozilla::OwningNonNull<U>& aOther)
+  : RefPtr(aOther.get())
+{}
+
+template<class T> template<class U>
+RefPtr<T>&
+RefPtr<T>::operator=(const mozilla::OwningNonNull<U>& aOther)
+{
+  return operator=(aOther.get());
+}
+
+#endif // mozilla_OwningNonNull_h