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Karen Etheridge > Class-Adapter > Class::Adapter::Clear



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Module Version: 1.09   Source  


Class::Adapter::Clear - A handy base Adapter class that makes no changes


version 1.09


Hello World with the normal way

  # Load and create the CGI
  use CGI;
  $q = new CGI;
  # Create the page
  print $q->header,                    # HTTP Header
        $q->start_html('hello world'), # Start the page
        $q->h1('hello world'),         # Hello World!
        $q->end_html;                  # End the page

Hello World with the Adapter'ed way

  # Load and create the CGI
  use CGI;
  $q = new CGI;
  # Convert to an Adapter
  use Class::Adapter::Clear;
  $q = new Class::Adapter::Clear( $q );
  # Create the page
  print $q->header,                    # HTTP Header
        $q->start_html('hello world'), # Start the page
        $q->h1('hello world'),         # Hello World!
        $q->end_html;                  # End the page

Creating a CGI Adapter class using Class::Adapter::Clear

  package My::CGI;
  use base 'Class::Adapter::Clear';
  # Optional - Create the thing we are decorating auto-magically
  sub new {
      my $class = shift;
      # Create the object we are decorating
      my $query = CGI->new(@_);
      # Wrap it in the Adapter
  # Decorate the h1 method to change what is created
  sub h1 {
        my $self = shift;
        my $str  = shift;
    # Do something before the real method call
    if ( defined $str and $str eq 'hello world' ) {
        $str = 'Hello World!';
    $self->_OBJECT_->($str, @_);


Class::Adapter::Clear provides the base class for creating one common type of Class::Adapter classes. For more power, move up to Class::Adapter::Builder.

On it's own Class::Adapter::Clear passes all methods through to the same method in the parent object with the same parameters, responds to ->isa like the parent object, and responds to ->can like the parent object.

It looks like a Duck, and it quacks like a Duck.

On this base, you simple implement whatever method you want to do something special to.

  # Different method, same parameters
  sub method1 {
      my $self = shift;
      $self->_OBJECT_->method2(@_); # Call a different method
  # Same method, different parameters
  sub method1 {
      my $self = shift;
      $self->_OBJECT_->method1( lc($_[0]) ); # Lowercase the param
  # Same method, same parameters, tweak the result
  sub method1 {
      my $self = shift;
      my $rv = $self->_OBJECT_->method1(@_);
      $rv =~ s/\n/<br>\n/g; # Add line-break HTML tags at each newline
      return $rv;

As you can see, the advantage of this full-scale Adapter approach, compared to inheritance, or function wrapping (see Class::Hook), is that you have complete and utter freedom to do anything you might need to do, without stressing the Perl inheritance model or doing anything unusual or tricky with CODE references.

You may never need this much power. But when you need it, you really need it.

As an aside, Class::Adapter::Clear is implemented with the following Class::Adapter::Builder formula.

  use Class::Adapter::Builder
      ISA      => '_OBJECT_',
      AUTOLOAD => 1;


new $object

As does the base Class::Adapter class, the default new constructor takes a single object as argument and creates a new object which holds the passed object.

Returns a new Class::Adapter::Clear object, or undef if you do not pass in an object.


Class::Adapter, Class::Adapter::Builder


Bugs may be submitted through the RT bug tracker (or


Adam Kennedy <>


This software is copyright (c) 2005 by Adam Kennedy.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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