"Thorsten Ottosen" <nesotto@cs.auc.dk> writes:
"David Abrahams" <dave@boost-consulting.com> wrote in message news:ur7pkurnp.fsf@boost-consulting.com... | "Thorsten Ottosen" <nesotto@cs.auc.dk> writes:
| > Let me explain a little better this tricky situation. Since the Range | > concepts are described in terms of free-standing functions, we kind of | > loose the ability to say a class is a model of a Range concept if that | > class only has member functions in its interface. | > | > So since Collection has col.begin() and col.end() and not begin( col ) | > and end( col ) it is not per se a model of any Range concept. | > | > Boost.Range then comes with an implementation of various Range | > concepts for *any* class that has begin() and end() members. So when | > this header with this implementation is included, all Collections | > model certain Range concepts; otherwise they do not. | > | > And since Ranges are complete decoupled from the class/member function | > idea, it does not make sense for classes to refine these concepts. | > | > hope it helps | | What we need is somthing like this: | | namespace boost { namespace range { | | namespace detail | { | template <class T> | typename range_iterator<T>::type begin(T& x) | { | return x.begin() | } | | template <class T> | typename range_iterator<T>::type adl_begin(T& x) | { | return begin(x); // will use ADL if a begin is defined | } | } | | template <class T> | typename range_iterator<T>::type begin(T& x) | { | return detail::adl_begin(x) | } | | }}
apart from the adl stuff, it already is like that. Did you mean to put in the range namespace to avoid problems with classes in boost?
No, I mean so that the concept can be described in terms of boost::range and Collection can become a refinement of Range.
| Then you change the Range concept to require that | boost::range::begin(col) works.
hm...yeah...one could perhaps state both syntaxes as part of the concept, eg
Valid expressions ============ begin( a ) or a.begin()
No, you have to say boost::range::begin(col). Otherwise they could make a.begin() valid but begin(a) invalid, and that would break boost::range::begin.
| Of course, Collection will only be a | refinement if there is no incorrect begin hanging around for that | type... so maybe this is fruitless.
well, I agree that we have not got it complete right yet.
perhaps the Range concept could specify
Primary Template Behavior ================== return a.begin()
?
Wha??? What do primary templates have to do with this?
And maybe we don't have to talk about collection as a refinement; maybe a new term is in order, like "act", sa in "all Collections may act as Ranges".
... provided that "..." Or, we could say that certain refinements of Collection are also refinements of Range. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com