2016-07-13 12:05 GMT+02:00 Ville Voutilainen <ville.voutilai...@gmail.com>: > On 13 July 2016 at 01:31, Jonathan Wakely <jwak...@redhat.com> wrote: >> On 11/07/16 23:41 +0300, Ville Voutilainen wrote: >>> >>> @@ -785,41 +785,60 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION >>> } >>> }; >>> >>> + template<typename _Tp> >>> + using __optional_relop_t = >>> + enable_if_t<is_constructible<bool, _Tp>::value, bool>; >> >> >> Should this be is_convertible<_Tp, bool> instead? > > Yeah.. it would be more reasonable to return a type explicitly > convertible to bool from a relop > if a non-bool is returned, but since built-in operators are not > contextually-convertible-to-bool, > that "protection" wouldn't buy much. And since the implementation > doesn't really do bool-wrappings > everywhere, let's go with is_convertible and change that if someone complains.
How would you feel about the introduction of an internal trait __is_boolean_testable, that would test both is_convertible<const T&, bool> and is_constructible<bool, const T&> for now, so that we could reuse that at places like these and others pointed out by LWG 2114? If you like that idea, I would work on a contribution. Thanks, - Daniel
