package Local::Class;
sub new
{
   my $class = shift;
   bless +{ A=>'default' };
}
sub access_A
{
   my ($self, $new_a) = @_;
   $self->{A} = $new_a if $new_a;
   return $self->{A};
}

package main;
use 5.010;

my $obj = Local::Class->new;

$obj->access_A(1);
say $obj->access_A;   # says 1

$obj->access_A(2);
say $obj->access_A;   # says 2

$obj->access_A(0);
say $obj->access_A;   # says 2 !!!