Learning Perl Objects, References, and Modules

A.9.1 Exercise (Section 10.7.1)

First, start the class:

{ package RaceHorse; our @ISA = qw(Horse);

Next, use a simple dbmopen to associate %STANDINGS with permanent storage:

dbmopen (our %STANDINGS, "standings", 0666) or die "Cannot access standings dbm: $!";

When a new RaceHorse is named, either pull the existing standings from the database or invent zeroes for everything:

sub named { # class method my $self = shift->SUPER::named(@_); my $name = $self->name; my @standings = split ' ', $STANDINGS{$name} "0 0 0 0"; @$self{qw(wins places shows losses)} = @standings; $self; }

When the RaceHorse is destroyed , the standings are updated:

sub DESTROY { # instance method, automatically invoked my $self = shift; $STANDINGS{$self->name} = "@$self{qw(wins places shows losses)}"; $self->SUPER::DESTROY; }

Finally, the instance methods are defined:

## instance methods: sub won { shift->{wins}++; } sub placed { shift->{places}++; } sub showed { shift->{shows}++; } sub lost { shift->{losses}++; } sub standings { my $self = shift; join ", ", map "$self->{$_} $_", qw(wins places shows losses); } }