C:\>perl -MDevel::Peek -e "$x = 0.5; qq/$x/; Dump $x" SV = PVNV(0x38bb4) at 0xd217cc REFCNT = 1 FLAGS = (NOK,pNOK) IV = 0 NV = 0.5 PV = 0xd16014 "0.5"\0 CUR = 3 LEN = 28 C:\>perl -MDevel::Peek -e "$x = 0; qq/$x/; Dump $x" SV = PVIV(0xd200c4) at 0xd2685c REFCNT = 1 FLAGS = (IOK,POK,pIOK,pPOK) IV = 0 PV = 0xd16274 "0"\0 CUR = 1 LEN = 10 #### use Benchmark qw/ cmpthese /; $x = 42.0; %h = (); cmpthese( -1, { F => sub { $h{ pack 'F', $x } = 1 }, s => sub { $h{ $x } = 1 }, }); #### Rate s F s 344025/s -- -86% F 2490475/s 624% --