It is noted in the POD for keys:

As a side effect, calling keys() resets the HASH's internal iterator, see each. (In particular, calling keys() in void context resets the iterator with no other overhead.)
Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
"Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon

In reply to Re^3: Optimization, side-effects and wrong code by BrowserUk
in thread Optimization, side-effects and wrong code by cbraga

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