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

by Anonymous Monk
on Mar 14, 2013 at 19:47 UTC ( #1023542=note: print w/ replies, xml ) Need Help??


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

I believe that for this exact case (for @array) it is safe, despite the warning which has been there very long time, and despite there being no tests for it

I've done it in 5.005 and 5.016 and it worked as expected :) and its perfectly logical, it can't go wrong ( unlike shrinking the size of the array)

I believe the only situation for which the warning applies is shrinking the array (pop/unshift), or replacing parts of it (splice)

http://search.cpan.org/dist/perl5.005/pod/perlsyn.pod#Foreach_Loops
http://perl5.git.perl.org/perl.git/blob/HEAD:/t/cmd/for.t
http://perl5.git.perl.org/perl.git/blob/HEAD:/t/op/push.t
http://perl5.git.perl.org/perl.git/blob/HEAD:/t/op/for.t
http://perl5.git.perl.org/perl.git/blob/HEAD:/t/op/each.t
http://perl5.git.perl.org/perl.git/blob/HEAD:/t/op/splice.t
#9336: Changing a for array dumps core
Deleting specific element in array in FOREACH loop

In any case, warnings doesn't warn you about iterating over an array while you splice over it, but it could

In any case, the tests should be amended to test out the possibilities, to narrow down what is safe and what isn't :) So write up a test and perlbug-it brave soul :)

Also a Perl::Critic policy should be easy to write, see Perl::Critic::Policy::ValuesAndExpressions::UndefinedBehaviourMaybeQuoteit / $1 not quoted (value not frozen) undefined behaviour


Comment on Re: Is it safe to append to the array you are iterating over (yes)
Re^2: Is it safe to append to the array you are iterating over (yes)
by DrWhy (Chaplain) on Mar 15, 2013 at 22:39 UTC
    I wouldn't be surprised now if even splice might not confuse the loop as long as you are splicing parts of the array that the loop iterator hasn't reached yet.

    --DrWhy

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

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