Object-oriented implementation in CGI-scripting is unpopular, as I discovered while trying to find a good guestbook script. I wanted a script that I could easily modify by changing the design, adding new features, etc., and that I could use to build a forum. Of the thirty free guestbook scripts on the Web, none was suitable for me. So I turned to object technology as a solution for reusable Web applications based on HTML templates.

Object and class relationships

Before designing the object model it is a good idea to examine existing CPAN (Comprehensive Perl Archive Network) modules that could be useful. The principal issue is the relationship between a newly created class and a CPAN module class. The relationship could be: a) a standard class object is included in the newly created class ("has-a" relationship), and less frequently b) the newly created class inherits from the standard class ("is-a" relationship).

The code listing below is an example of a constructor for My class, which inherits from BaseClass. Moreover, My class contains AnotherClass object, which is private (the name begins with underline character -- a convention not enforced by Perl itself).

package My;
require BaseClass; #required if BaseClass is present in BaseClass.pm
@ISA=qw(BaseClass);
use AnotherClass;
sub new {
	my $package=shift;
	my $self=$package->SUPER::new($package); #create object in BaseClass
	$self->{_another_class_object}=new AnotherClass;
	$self;
}

package My;
require BaseClass; #required if BaseClass is present in BaseClass.pm
@ISA=qw(BaseClass);
use AnotherClass;
sub new {
	my $package=shift;
	my $self=$package->SUPER::new($package); #create object in BaseClass
	$self->{_another_class_object}=new AnotherClass;
	$self;
}

package AbstractCGI;
sub new {
	my $package=shift;
	my $self={
		_cgi_method=>undef, #simple class data
		_query=>undef
	};
	bless $self, ref $package || $package;
	$self->_init;
	$self;
}
sub _init {die} #private method
sub get_param {die}
sub is_print_form_mode { shift->get_param('mode') eq 'form' }
sub is_print_entries_mode { shift->get_param('mode') eq 'entries' }

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• Object and class relationships
• About the author
• Comments

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