RefCounted types should not have public destructors

base/memory/ref_counted.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MEMORY_REF_COUNTED_H_
 #define BASE_MEMORY_REF_COUNTED_H_
 #pragma once
 
 #include <cassert>
 
@@ skipping 146 matching lines @@
 // A wrapper for some piece of data so we can place other things in
 // scoped_refptrs<>.
 //
 template<typename T>
 class RefCountedData : public base::RefCounted< base::RefCountedData<T> > {
  public:
   RefCountedData() : data() {}
   RefCountedData(const T& in_value) : data(in_value) {}
 
   T data;
+
+ protected:
+  ~RefCountedData() {}

[darin (slow to review), 2012/05/22 18:01:31]

probably you want to make this destructor virtual or private.  otherwise,
someone will be sad if they try to inherit from RefCountedData.

[Ryan Sleevi, 2012/05/22 18:36:20]

See the thread I started on chromium-dev regarding destructors.

Making it private means that this cannot be inherited (as ResourceResponse wants
to do). Making it virtual seems to support polymorphic deletion, but that's
explicitly what we don't want to allow (see the chromium-dev thread).

This is following http://www.gotw.ca/publications/mill18.htm

" A base class destructor should be either public and virtual, or protected and
nonvirtual."

+
+ private:
+  friend class base::RefCounted<base::RefCountedData<T> >;
 };
 
 }  // namespace base
 
 //
 // A smart pointer class for reference counted objects.  Use this class instead
 // of calling AddRef and Release manually on a reference counted object to
 // avoid common memory leaks caused by forgetting to Release an object
 // reference.  Sample usage:
 //
@@ skipping 119 matching lines @@
 };
 
 // Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
 // having to retype all the template arguments
 template <typename T>
 scoped_refptr<T> make_scoped_refptr(T* t) {
   return scoped_refptr<T>(t);
 }
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_