Hi Gabriel, I proposed a similar function at the time of introducing the warning, but it doesn't look like I got around to creating an RFC for it: https://github.com/php/php-src/pull/2206/files
During this work we realised that objects don't have to implement the '\Countable' interface to be successfully handled by 'count()', internal/extension classes can implement a 'count_elements' handler and ignore the interface. I'd suggest that 'is_countable()' should be consistent with 'count()'. Thanks, Craig
