Vicente Botet wrote:
Le 20/10/11 17:09, Jeffrey Lee Hellrung, Jr. a écrit :
On Thu, Oct 20, 2011 at 7:55 AM, lcaminiti<lorcaminiti@> wrote:
Hello all,
has_equal_to< std::vector<T> > always returns true_ because == is defined for std::vector<T> even when it is not defined for T. However, then an attempt to compare for equality std::vector<T> will generate a compiler error in this case because there is no == for T.
<snip>
Shall has_equal_to< std::vector<T> > be smarter and return false_ if T does not have == ? (If not, this case should at least be documented.)
I'd venture to say this is a deficiency in std::vector's implementation of operator==, which ideally should SFINAE-out bindings of T which do not have an operator==. <snip>
In my opinion, the upshot is that std::vector's operator== is almost certainly not a special case, so I don't know know if it's worth specializing has_equal_to on it or not. Maybe, if it's consistently done for all problematic std-defined operators?
Hi,
I found the same kind of issues while implementing is_constructible/is_assignable/is_convertible for Boost.Conversion. The option I taken was to specialize these traits for the c++ implementations that were not using SFINAE. This force of course the user to include the specific file containing the specialization.
Would the Boost.TypeTraits authors consider adding the specializations* to workaround STL not using SFINAE? If not, can these cases be documented? (*) In this case it'd be nice to name the headers containing the extra specialization consistently with other Boost libraries like Boost.Conversion-- Vicente, how did you name the headers containing the specialization for the STL types? Thanks. --Lorenzo -- View this message in context: http://boost.2283326.n4.nabble.com/boost-type-traits-has-equal-to-std-vector... Sent from the Boost - Dev mailing list archive at Nabble.com.