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Rather than creating complex inheritance trees, consider creating a generic serialization interface for your shopping cart and put the serializer in your cart object.

# Create the cart my $cart = new Cart( type => 'DBI', id => $foo ); print "Cart's current total is: ", $cart->total_cost(); # Be sure we don't sell anything inappropriate! foreach my $item ( $cart->list_items ) { if ( $item->type eq 'adult' && $user->age < 18 ) { $cart->remove_item( $item ); } } $cart->save; print "Cart's new total is: ", $cart->total_cost();

Using something like (ahem!) Class::Factory, the initialization and some of the cart code might look like:

package Cart; # 'id', 'serializer' are accessor/mutator functions # like those created by Class::Accessor sub new { my ( $class, %params ) = @_; my $self = bless( {}, $class ); $self->id( $params{id} ); my $serializer = Cart::Serializer->new( $params{type}, $id ); $self->serializer( $serializer ); return $self; } sub list_items { ... } sub add_item { ... } sub remove_item { ... } sub total_cost { ... } sub save { my ( $self ) = @_; my $serializer = $self->serializer; $serializer->save( $self ); } package Cart::Serializer; use base qw( Class::Factory ); my %TYPES = ( DBI => 'Cart::Serializer::DBI', LDAP => 'Cart::Serializer::LDAP', File => 'Cart::Serializer::File' ); sub get_factory_map { return \%TYPES }; sub save { die "Implement in subclass!" } package Cart::Serializer::DBI; sub init { my ( $self, $id ) = @_; # ... do DBI fetch ... } sub save { my ( $self, $cart ) = @_; # ... save to DBI table ... } package Cart::Serializer::LDAP; sub init { my ( $self, $id ) = @_; # ... do LDAP fetch ... } sub save { my ( $self, $cart ) = @_; # ... save to LDAP tree ... } package Cart::Serializer::File; sub init { my ( $self, $id ) = @_; # ... read from filesystem } sub save { my ( $self, $cart ) = @_; # ... save to filesystem ... }

Hopefully this makes some sense. I have on my wall three of the core ideas from the Gang of Four book, and the second one is Favor composition over inheritance, which I try to follow whenever possible. "Think about loose coupling" and all that :-)

Chris
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In reply to Re: OOP: Plugin Style Development by lachoy
in thread OOP: Plugin Style Development by jk2addict

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