1 files changed, 78 insertions, 0 deletions
diff --git a/widget/windows/CheckInvariantWrapper.h b/widget/windows/CheckInvariantWrapper.h
new file mode 100644
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+++ b/widget/windows/CheckInvariantWrapper.h
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+/* -*- 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 wrapper that uses RAII to ensure that a class invariant is checked
+// before and after any public function is called
+
+#ifndef CHECKINVARIANTWRAPPER_H_
+#define CHECKINVARIANTWRAPPER_H_
+
+#include "mozilla/Attributes.h"
+#include <utility>
+
+namespace mozilla {
+
+//
+// Wraps an object of type T and allows access to its public API by
+// deferencing it using the pointer syntax "->".
+//
+// Using that operator will return a temporary RAII object that
+// calls a method named "CheckInvariant" in its constructor, calls the
+// requested method, and then calls "CheckInvariant" again in its
+// destructor.
+//
+// The only thing your class requires is a method with the following signature:
+//
+// void CheckInvariant() const;
+//
+template <typename T>
+class CheckInvariantWrapper {
+ public:
+  class Wrapper {
+   public:
+    explicit Wrapper(T& aObject) : mObject(aObject) {
+      mObject.CheckInvariant();
+    }
+    ~Wrapper() { mObject.CheckInvariant(); }
+
+    T* operator->() { return &mObject; }
+
+   private:
+    T& mObject;
+  };
+
+  class ConstWrapper {
+   public:
+    explicit ConstWrapper(const T& aObject) : mObject(aObject) {
+      mObject.CheckInvariant();
+    }
+    ~ConstWrapper() { mObject.CheckInvariant(); }
+
+    const T* operator->() const { return &mObject; }
+
+   private:
+    const T& mObject;
+  };
+
+  CheckInvariantWrapper() = default;
+
+  MOZ_IMPLICIT CheckInvariantWrapper(T aObject) : mObject(std::move(aObject)) {}
+
+  template <typename... Args>
+  explicit CheckInvariantWrapper(std::in_place_t, Args&&... args)
+      : mObject(std::forward<Args>(args)...) {}
+
+  const ConstWrapper operator->() const { return ConstWrapper(mObject); }
+
+  Wrapper operator->() { return Wrapper(mObject); }
+
+ private:
+  T mObject;
+};
+
+}  // namespace mozilla
+
+#endif  // CHECKINVARIANTWRAPPER_H_