https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71899
Bug ID: 71899 Summary: An internal BooleanTestable trait should be provided Product: gcc Version: 6.0 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: daniel.kruegler at googlemail dot com Target Milestone: --- I suggest to provide an internal type trait that corresponds to the currently discussed BooleanTestable requirement set as described in LWG 2743: http://cplusplus.github.io/LWG/lwg-active.html#2743 This trait could be used in SFINAE-constraints such as for the recently added comparison functions of std::optional or as argument of static_assert for the existing comparison functions of std::tuple and possibly other places as well. In the absence of any better name, I suggest to introduce a type trait named __is_boolean_testable in header <type_traits>. Given that LWG 2743 is not resolved yet, I recommend to start with a very weak set of requirements for some type T, e.g. the logical AND of std::is_convertible<const T&, bool>::value std::is_constructible<bool, const T&>::value I'm willing to provide this contribution.