Re^2: Is it safe to append to the array you are iterating over

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..."

Comment on Re^2: Is it safe to append to the array you are iterating over

Replies are listed 'Best First'.
Re^3: Is it safe to append to the array you are iterating over by ikegami (Patriarch) on Mar 16, 2013 at 19:53 UTC
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";` [download] 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";` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^3: Is it safe to append to the array you are iterating over
by ikegami (Patriarch) on Mar 16, 2013 at 19:53 UTC

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";
[download]

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";
[download]

[reply]
[d/l]
[select]