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Re: Is it safe to append to the array you are iterating over

by SuicideJunkie (Vicar)
on Mar 14, 2013 at 17:27 UTC ( #1023513=note: print w/replies, xml ) Need Help??


in reply to Is it safe to append to the array you are iterating over

If you don't mind consuming the array:

while (@array) { $item = shift @array; ... push @array, @newstuff; }
or a manual index value to preserve the array contents:
for (my $i=0; $i< $#array; $i++) { ... push @array, $thing if desired(); }

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Re^2: Is it safe to append to the array you are iterating over
by DrWhy (Chaplain) on Mar 14, 2013 at 19:03 UTC
    I've decided to change my code to instead use a while loop/shift solution similar to what you suggested. It's approximately as simple as my original and doesn't have this issue of possibly depending on an undocumented implementation detail of my version of Perl.

    --DrWhy

    "If God had meant for us to think for ourselves he would have given us brains. Oh, wait..."

      possibly depending on an undocumented implementation detail of my version of Perl.

      You most definitely are. The loop is suppose to take a list over which to iterate, but you're relying on the observable differences between that an the actual optimised implementation. You can see this by changing foreach (@arr) to what should be equivalent foreach ((),@arr).

      Either iterate over the indexes

      my @arr = qw/a b c/; for (my $i=0; $i<@arr; ++$i) { my $e = $arr[$i]; push @arr, 'd' if $e eq 'a'; push @arr, 'e' if $e eq 'b'; push @arr, 'f' if $e eq 'c'; print $e; } print "\n";

      Or use a queue

      my @arr = qw/a b c/; while (@arr) { my $e = shift(@arr); push @arr, 'd' if $e eq 'a'; push @arr, 'e' if $e eq 'b'; push @arr, 'f' if $e eq 'c'; print $e; } print "\n";

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