Question

I would like to have a template on container and two tuple types, so that I can merge two following functions into one:

template<typename Container>
void vblock(int row, int col, const Container& container) {
  foreach( const typename Container::value_type& item, container ) {
    cell(row, col, item);
    ++row;
  }
}

template<typename container, typename T1, typename T2>
void vblock(int row, int col,
          const std::list<typename boost::tuple<T1, T2> >& container) {
  typedef boost::tuple<T1, T2> Tuple;
  foreach( const Tuple& item, container ) {
    cell(row, col, item.template get<0>());
    cell(row + 1, col, item.template get<1>());
    ++col;
  }
}

template<typename container, typename T1, typename T2>
void vblock(int row, int col,
          const std::set<typename boost::tuple<T1, T2> >& container) {
  typedef boost::tuple<T1, T2> Tuple;
  foreach( const Tuple& item, container ) {
    cell(row, col, item.template get<0>());
    cell(row + 1, col, item.template get<1>());
    ++col;
  }
}

I have already checked C++ Templates – Specifying a container type and that containers element type that it holds and C++ Template class using STL container and a typedef, but they don’t answer my question.

The question simple C++ templates suited for STL Containers is most similar to mine, but I couldn’t figure out how to add templates for boost::tuple. Thanks!

Answer 1

Keep it simple:

template <typename C>
void vblock(int row, int col, C const & container)
{
    typedef typename C::value_type tuple_type;
    typedef typename boost::element<0, tuple_type>::type first_type;
    typedef typename boost::element<1, tuple_type>::type second_type;

    // ...
}

You could add some enable_if logic to the function declaration to prevent the creation of impossible overloads, but perhaps that’s not needed just yet.