I can say that it's not a good idea. Look at what you get when you do this: 
my @foo = qw/a b c d e f g/;
for my $x (@foo) {
    push @foo, 'd' if $x eq 'd';
    print $x;
}

[download]
The iterator keeps marching through the d's, adding new ones to the end. A better way to do it might be: 
push @foo, map {$_ eq 'd' ? 'd' : ()} @foo;
print for @foo;

[download]
I doubt that it's implmentation-dependent. The iterator is stepping through the array, and by the time it gets to the end of the array, there's another element there to step through.

Still, it's not a nice trick to play. Here's an even more diabolical one: 

for (@foo) {
  print;
  shift(@foo) if $_ eq 'c';
}
print "\n@foo\n";

[download]
Caution: Contents may have been coded under pressure.

In reply to Re: changing array size in foreach loop: is it safe? by Roy Johnson
in thread changing array size in foreach loop: is it safe? by Errto

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