$ 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.

--