Perl does cache whether an SV contains something usable as an integer (the IOK flag) or a floating point number (the NOK flag). That's why you almost never see

Perl does cache whether an SV contains something usable as an integer (the IOK flag) or a floating point number (the NOK flag). That's why you almost never see `looks_like_number` on its own and always called after using one of the appropriate flag checking macros.