C++Talk.NET

Joe Gottman · Guest

I just realized that there's a subtle difference between classes and
concepts that might affect the "more specialized" relationship that is
used for overload resolution. Classes use inheritance to model the "isa"
relationship.

class A {}
class B : public A {} // All B's are A's.

We can can do the same thing with concepts, although in this case it is
called refinement.

concept InputIterator<typename Iter> { }
concept ForwardIterator<typename Iter> : InputIterator<Iter> { }
//All ForwardIterators are InputIterators

However there's another, completely different way to make two concepts
model the "isa" relationship: concept_maps.

concept Range<typename R> {}
concept Container<typename C> {}

template <Container C> concept_map Range<C> { } //All Containers are
Ranges.

In this case, is the Container concept considered to be more specialized
than the Range concept for overload resolution? Can I define the
following overload set:

template <Range R> inline std::size_t size(const R &r);
template <Container C> inline std::size_t size(const C &c);

and have the second function called for all Containers and the first one
called for all Ranges that aren't Containers? If I can't do it
directly, will the following variation work?

template <Range R> inline std::size_t size(const R &r);
template <Range R> requires Container<R>
inline std::size_t size(const R &r);

Joe Gottman

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Douglas Gregor · Guest

On May 13, 8:51 am, jgott...@carolina.rr.com (Joe Gottman) wrote: