http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51336
--- Comment #7 from Daniel Krügler <daniel.kruegler at googlemail dot com>
2011-11-29 10:50:37 UTC ---
(In reply to comment #5)
> All right, now the is_abstract behavior is settled, do you think the fixed
> code
> provided by Daniel in comment #1 should produce a warning, since the
> declaration is absolutely useless (I may be missing something)?
IMO a warning could be very useful here (at least in circumstances where the
constructor is never reachable).
> Or maybe there are legitimate meta-programming tricks I am not thinking of
> that
> would turn regular constructors into pseudo copy constructors to disable them?
While it seems that the current defect in regard to concept-constrained member
functions mentioned in c++std-core-20783 is a defect, so that
template<ObjectType T>
class A {
requires SomeConcept<T>
A(const A&) {}
};
is *intended* to work, I currently see no such chance for sfinae-constrained
special-member functions - unless the new temploid nomenclature shows that in
template<class T>
struct A {
template<class U = T, class = typename
std::enable_if<std::is_same<U, int>::value>::type
>
A(A const&){}
};
A<T>::A(A const&) is considered as a temploid as well. I stay tuned to see how
"temploids" will be defined...
Your suggested addition of a copy-constructor to non-const is surely useful in
some cases, but I think the emulation is imperfect. Just consider that you try
to copy from a source that is not const.
