Searching in a set of shared_ptr<QString>

Question

I have an object:

class Object {
public:
  boost::shared_ptr<QString> const& name() const {reutrn _name;}
private:
  boost::shared_ptr<QString> _name;
};

And a multi_index set

typedef
    boost::multi_index_container<
        Object,
        boost::multi_index::indexed_by<
            boost::multi_index::ordered_unique<
                boost::multi_index::const_mem_fun<
                    Object,
                    boost::shared_ptr<QString> const&,
                    & Object::name>,
                StringPointerLess> > >
    ObjectSet;

Now If I want to find something in the set and I have QString I need to make a copy of it to allocate in heap and create shared_ptr.

Is it possible to avoid this unnecessary copy operation, leaving the set as it is?

Answer 1

A simpler way: add the following member functions to your StringPointerLesscomparison predicate:

struct StringPointerLess{
  ...
  bool operator()(boost::shared_ptr<QString> const& x,const QString& y)const{
    return *x<y;
  }
  bool operator()(const QString& x,boost::shared_ptr<QString> const& y)const{
    return x<*y;
  }
  ...
};

and now you can lookup by simply providing the desired QString:

IteratorType find( MyContainerType const& container, QString const& key )
{
   return container.find( key );
}

The magic behind this is explained at the special lookup operations section in Boost.MultiIndex documentation.