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.
