I also like curlies around the grep block

Without curlies, it is not a block. The non-block version of grep is much faster.

2;0 juerd@ouranos:~$ perl -MBenchmark=cmpthese -e'cmpthese(-1, { block
+ => sub { grep { /[13579]/ } 0..9 }, nonblock => sub { grep /[13579]/
+, 0..9 } })'
[download]

Benchmark: running block, nonblock, each for at least 1 CPU seconds...
     block:  2 wallclock secs ( 1.06 usr +  0.00 sys =  1.06 CPU) @ 44436.79/s (n=47103)
  nonblock:  0 wallclock secs ( 1.01 usr +  0.00 sys =  1.01 CPU) @ 141940.59/s (n=143360)
             Rate    block nonblock
block     44437/s       --     -69%
nonblock 141941/s     219%       --

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