Created attachment 35238 [details]
patch to add operator< and qHash

When you try to use a SharedPtr in a QMap as follows:
  QMap<Tp::SharedPtr<T>, int>

The compiler will happily allow you to do so.  However, when running the application, you'll notice some strange behavior.  note that QMap (like std::map) requires that the type used for a key have operator< defined in order to determine the order of th eelements in the map.  tp-qt4 does not provide operator< for SharedPtrs, so the compiler looks for a suitable comparison operator and notices that SharedPtr can be implicitly converted to bool (due to the unfortunate definition of 'SharedPtr::operator bool()') and so it uses the following operator to determine element order:
  operator<(bool a, bool b)

So when you insert a new element into the map, it will compare the new key with the old key by first converting them to booleans.  The impact of this is that any non-null sharedptr will be interpreted as being the exact same key value.  This means that the maximum number of elements in this map is 2: one non-null SharedPtr and one null SharedPtr.  A user can define an appropriate operator< herslef, but it's not immediately obvious that this is necessary.  It would be good if the library itself provided the comparison operator.  I'm providing a patch that adds a few comparison operators and a qHash() implementation for SharedPtr.

Note that this does not fix all of the unfortunate consequences of defining the 'operator bool()', since the following line will still happily compile despite it being quite obviously nonsense:
  int i = SharedPtr<T>(new T());

But that's a different bug report...