On 5/27/2010 12:57 PM, Lorenzo Caminiti wrote:
On Thu, May 27, 2010 at 1:48 PM, Jeffrey Lee Hellrung, Jr. <jhellrung@ucla.edu> wrote:
On 5/27/2010 10:38 AM, Lorenzo Caminiti wrote:
N2081 briefly mentions this can be done in C++ using SFINAE, etc. I think I could use `enable_if` if I had some sort of `is_input_iterator` metafunction... Please just point me to the documentation if this has already been addressed there.
Do you mean the iterator_category / iterator_traversal metafunctions in boost/iterator/iterator_traits.hpp ? [...]
http://www.boost.org/libs/iterator/doc/iterator_traits.html
template< class Iterator> typename boost::disable_if< boost::is_convertible< typename boost::iterator_traversal< Iterator>::type, boost::bidirectional_traversal_tag >
::type advance(...) { ... } // for IncrementableIterator's
template< class Iterator> typename boost::enable_if< boost::is_convertible< typename boost::iterator_traversal< Iterator>::type, boost::bidirectional_traversal_tag >
::type advance(...) { ... } // for BidirectionalIterator's
I think the primary way to currently effect "concept-based" overloading is via tags or similar metafunction-based methods. There do exist introspection techniques, though, such as proto's can_be_called or is_incrementable in boost/detail/, so it is possible to overload based on (some) syntactic properties.
Is that what you're looking for?
Essentially, the above code from Jeff got the job done for what I needed. I used `enabled_if` and tagging.
Also thanks to everyone else for the very informative comments.
Just so an "inferior" approach isn't mistaken as the "correct" solution, Thomas is right, you should use tag-dispatching if possible: template< class Iterator > void advance_dispatch(..., boost::incrementable_traversal_tag) { ... } template< class Iterator > void advance_dispatch( ..., boost::bidirectional_traversal_tag) { ... } template< class Iterator > void advance(...) { advance_dispatch(..., typename iterator_traversal< Iterator >::type()); } And now that I've written this, I see this exact example is already elaborated on at the boost website: http://www.boost.org/community/generic_programming.html#tag_dispatching Sorry for any misdirection, - Jeff