The Pragma Interface¶

The most common method for defining Adapter classes, as shown in the synopsis, is the pragma interface.

This consists of a set of key/value pairs provided when you load the module.

  # The format for building Adapter classes
  use Class::Adapter::Builder PARAM => VALUE, ...

ISA

The "ISA" param is provided as either a single value, or a reference to an "ARRAY" containing is list of classes.

Normally this is just a straight list of classes. However, if the value for "ISA" is set to '_OBJECT_' the object will identify itself as whatever is contained in it when the "->isa" and "->can" method are called on it.

NEW

Normally, you need to create your "Class::Adapter" objects separately:

  # Create the object
  my $query = CGI->new( 'param1', 'param2' );
  
  # Create the Decorator
  my $object = My::Adapter->new( $query );
    

If you provide a class name as the "NEW" param, the Decorator will do this for you, passing on any constructor arguments.

  # Assume we provided the following
  # NEW => 'CGI',
  
  # We can now do the above in one step
  my $object = My::Adapter->new( 'param1', 'param2' );
    

AUTOLOAD

By default, a "Class::Adapter" does not pass on any methods, with the methods to be passed on specified explicitly with the 'METHODS' param.

By setting "AUTOLOAD" to true, the "Adapter" will be given the standard "AUTOLOAD" function to to pass through all unspecified methods to the parent object.

By default the AUTOLOAD will pass through any and all calls, including calls to private methods.

If the AUTOLOAD is specifically set to 'PUBLIC', the AUTOLOAD setting will ONLY apply to public methods, and any private methods will not be passed through.

METHODS

The "METHODS" param is provided as a reference to an array of all the methods that are to be passed through to the parent object as is.

Any params other than the ones specified above are taken as translated methods.

  # If you provide the following
  # foo => bar
  
  # It the following are equivalent
  $decorator->foo;
  $decorator->_OBJECT_->bar;

This capability is provided primarily because in Perl one of the main situations in which you hit the limits of Perl's inheritance model is when your class needs to inherit from multiple different classes that containing clashing methods.

For example:

  # If your class is like this
  package Foo;
  
  use base 'This', 'That';
  
  1;

If both "This->method" exists and "That->method" exists, and both mean different things, then "Foo->method" becomes ambiguous.

A "Class::Adapter" could be used to wrap your "Foo" object, with the "Class::Adapter" becoming the "That" sub-class, and passing "$decorator->method" through to "$object->that_method".