Your example is breaking encapsulation. That is, it is avoiding the accessor and reaching in to the internals. If we have the object:

package OOtest;
sub new {
   my $invoker = shift;
   my $class = ref($invoker) || $invoker;
   my $self  = {};
   bless ($self, $class);
   $self->{list}  = [];
   return $self;
}

sub get_array {
   my $self = shift;
   return $self->{list};
}
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To access the array, use the accessor get_array and do not bypass it by delving in and directory accessing the private variable.

my $obj = OOtest->new();
# NOT foreach my $tmp ( @{ $obj->list() } 
foreach my $tmp ( @{ $obj->get_array() } ) {
   # process list
}
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Now, internally, you want to change OOtest to use a hash, but you do not want to break other code that expects it to use (and wants) an array. Behold the beauty of accessors, you merely change the get_array subroutine.

package OOtest;
sub new {
   my $invoker = shift;
   my $class = ref($invoker) || $invoker;
   my $self  = {};
   bless ($self, $class);
   $self->{list}  = ();
   return $self;
}

sub get_array {
   my $self = shift;
   return values %{$self->{list}}; # anything asking for an array gets
+ it
}
[download]

enoch