[This post delves into the internals of Perls. Most won't find it useful, but some might find it interesting.]

I've used the following to process the contents of an array while emptying it:

f( splice(@a) )
[download]

Someone asked what @a, @a=() did on StackOverflow. Well, that's the what the title of their question was, but the actual question was a bit different. But I thought it might be an alternative to splice(@a), so I put it to the test.

$ perl -e'
   use strict;
   use warnings;
   use feature qw( say );

   my @a = qw( a b c d );
   say for @a, @a=();
   say "--";
   say for @a;
'
Use of freed value in iteration at -e line 7.
[download]

That was a first for me! Anyone want to venture a guess as to why it does that?

Note that the problem is not specific to loops, contrary to what your research might initially lead you to believe.

$ perl -e'
   use strict;
   use warnings;
   use feature qw( say );

   my @a = qw( a b c d );
   my @b = ( @a, @a=() );
   say for @b;
   say "--";
   say for @a;
'
Use of uninitialized value $_ in say at -e line 8.

Use of uninitialized value $_ in say at -e line 8.

Use of uninitialized value $_ in say at -e line 8.

Use of uninitialized value $_ in say at -e line 8.

--
[download]

Hint: The following avoids the problem:

$ perl -e'
   use strict;
   use warnings;
   use feature qw( say );

   my @a = qw( a b c d );
   my $r = sub{ \@_ }->(@a);
   say for @a, @a=();
   say "--";
   say for @a;
'
a
b
c
d
--
[download]

I'll post the answer.

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