Only some of those are true.

It is true that foreach over (@array) uses the original array as a list. It is also true that foreach over (1..1_000_000) does not build a list of a million entries. But the file construct most assuredly does slurp a file. Try running the following command-lines interactively to show that: 

perl -e '$| = 1; print while <>'

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vs 
perl -e '$| = 1; print foreach <>'

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You will find that the first spits back your lines interactively. The second has to wait to slurp up everything you have to say before it starts printing.

Should you ever need to write a filter for dealing with a large amount of data, be very, very careful to use while instead of foreach!

But a random note. If you check the benchmark, you will find that keys ran faster, 423.73 iterations per second vs 356.01. If memory is not a constraint, then for hashes of this size, foreach is faster!

In reply to RE (tilly) 3: each or keys? by tilly
in thread each or keys? by rdw

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