use Person;
$him = new Person;
$him->name("Jason");
$him->age(23);
$him->peers( ["Norbert", "Rhys", "Phineas"] );
printf "%s is %d years old.\n", $him->name, $him->age;
print "His peers are: ", join(", ", @{$him->peers}), ".\n";
*****
package Person;
use Carp;       # see Carp.pm in chapter 7

my %fields = (
    name        => undef,
    age         => undef,
    peers       => undef,
);

sub new {
    my $that  = shift;
    my $class = ref($that) || $that;
    my $self  = {
        _permitted => \%fields,
        %fields,
    };
    bless $self, $class;
    return $self;
} 

sub AUTOLOAD {
    my $self = shift;
    my $type = ref($self) || croak "$self is not an object";
    my $name = $AUTOLOAD;
    $name =~ s/.*://;   # strip fully-qualified portion
    unless (exists $self->{_permitted}->{$name} ) {
        croak "Can't access `$name' field in object of class $type";
    } 
    if (@_) {
        return $self->{$name} = shift;
    } else {
        return $self->{$name};
    } 
}