[Bug libstdc++/71899] An internal BooleanTestable trait should be provided

["ville.voutilainen at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71899

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |ville.voutilainen at gmail dot com

--- Comment #2 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
I dislike the #ifdef parts. It seems to me both modes of operation
could be provided without resorting to the preprocessor. I'm also
not a fan of the name boolean_testable - perhaps boolean_like would
be better? The rationale being that there are "boolean testable" types
that work in cases where a contextual conversion to bool is performed,
but those types are otherwise not "boolean-like". Sure, we could
go with boolean_testable and potentially contextually_boolean_testable
or some such. It seems to me that both of those facilities are useful.

I do wonder why we even bother supporting e.g. comparison operators that
don't just return bool, although that's in some ways a separate matter.