Best way to iterate through a Perl array

Question

Which is the best implementation(in terms of speed and memory usage) for iterating through a Perl array? Is there any better way? (@Array need not be retained).

Implementation 1

foreach (@Array) {       SubRoutine($_); } 

Implementation 2

while($Element=shift(@Array)) {       SubRoutine($Element); } 

Implementation 3

while(scalar(@Array) !=0) {       $Element=shift(@Array);       SubRoutine($Element); } 

Implementation 4

for my $i (0 .. $#Array) {       SubRoutine($Array[$i]); } 

Implementation 5

map { SubRoutine($_) } @Array ; 

Answer 1

• 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.

• 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.

• In terms of flexibility: #1/#4 and #5.

  #2 does not support elements that are false. #2 and #3 are destructive.

Answer 2

If you only care about the elements of @Array, use:

for my $el (@Array) { # ... } 

or

If the indices matter, use:

for my $i (0 .. $#Array) { # ... } 

Or, as of perl 5.12.1, you can use:

while (my ($i, $el) = each @Array) { # ... } 

If you need both the element and its index in the body of the loop, I would expect using each to be the fastest, but then you'll be giving up compatibility with pre-5.12.1 perls.

Some other pattern than these might be appropriate under certain circumstances.