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In terms of speed: #1 and #4, but not by much in most instances.
You could write a benchmark to confirm, but I suspect you’ll find #1 and #4 to be slightly faster because the iteration work is done in C instead of Perl, and no needless copying of the array elements occurs. (
$_is aliased to the element in #1, but #2 and #3 actually copy the scalars from the array.)#5 might be similar.
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In terms memory usage: They’re all the same except for #5.
for (@a)is special-cased to avoid flattening the array. The loop iterates over the indexes of the array. -
In terms of readability: #1.
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In terms of flexibility: #1/#4 and #5.
#2 does not support elements that are false. #2 and #3 are destructive.
