Benchmark: running substr, vec for at least 60 CPU seconds...
    substr: 62 wallclock secs (61.69 usr +  0.05 sys = 61.74 CPU) @  0.44/s (n=27)
       vec: 61 wallclock secs (60.81 usr +  0.05 sys = 60.86 CPU) @  0.39/s (n=24)
       s/iter    vec substr
vec      2.54     --   -10%
substr   2.29    11%     --