Bench as a standalone iterator step.

[RCasatta]

That's why I had benching as a standalone iterator step.

https://github.com/dpc/block-iter/blob/40578bb5eca918e7570b8ab82370ee88cebb7a9f/libs/main/src/bench.rs#L6

so one can insert .bench_x() at the end of a middle of an iterator chain and get stats. Though I now see that I forgot to make the bench_x be an iterator that returns the items it's benching, so right now it only works at the end, as a sort of of a .for_each() or .count().

Originally posted by @dpc in #42 (comment)