Benchmark: timing 20 iterations of for, hash...
       for: 16 wallclock secs (15.67 usr +  0.00 sys = 15.67 CPU) @  1.28/s (n=20)
      hash:  8 wallclock secs ( 8.57 usr +  0.04 sys =  8.61 CPU) @  2.32/s (n=20)
       Rate  for hash
for  1.28/s   -- -45%
hash 2.32/s  82%   --