On 4/15/06, David Abrahams <dave@boost-consulting.com> wrote:
"Daniel Walker" <daniel.j.walker@gmail.com> writes:
On 4/11/06, David Abrahams <dave@boost-consulting.com> wrote:
Thorsten Ottosen <thorsten.ottosen@dezide.com> writes:
cannot have overloads (in C++98) taking containers/ranges:
fn( Iterator first, Iterator last ) fn( Iterator first, Iterator last, Functor f ) fn( Range rng ) fn( Range rng, Functor f )
as the last overload is ambiguous. Concepts will allow this to be resolved as a Functor will not match the Iterator requirements :).
you can use enable_if on the latter and disable it the two types are the same.
Not if you happen to have a type that is both a valid range and a valid function object.
Yes, that's a corner case, but it's the corner of a large floating block of ice.
For this idiom, I use boost::iterator_range like so,
fn( Iterator first, Iterator last ) fn( Iterator first, Iterator last, Functor f ) fn( boost::iterator_range<Iterator> rng ) fn( boost::iterator_range<Iterator> rng, Functor f )
This is not generic. Now you can't pass other valid Ranges (e.g. std::vector<T>) as the first argument to fn.
Yeah, I know. This is just a work-around because the generic version isn't possible today due to the overload ambiguity. You can indirectly use the functions with other valid Ranges like vector, but it's a hassle because you first have to convert them using make_iterator_range(). In some circumstances, for the time being, this may be acceptable for this particular idiom (overloading algorithms to take both iterators and ranges), but really I agree that it further illustrates the need for in-language support for concepts in a future version of C++ in order to make the overloads generic. Daniel Walker