Name

Class::Delegator - Simple and fast object-oriented delegation

Synopsis

  package Car;

  use Class::Delegator
      send => 'start',
      to   => '{engine}',

      send => 'power',
      to   => 'flywheel',
      as   => 'brake',

      send => [qw(play pause rewind fast_forward shuffle)],
      to   => 'ipod',

      send => [qw(accelerate decelerate)],
      to   => 'brakes',
      as   => [qw(start stop)],
  ;

Description

This module provides a subset of the functionality of Damian Conway's lovely Class::Delegation module. Why a subset? Well, I didn't need all of the fancy matching semantics or dispatching to multiple delegated attributes, just string string specifications to map delegations. Furthermore, I wanted it to be fast. And finally, since Class::Delegation uses an INIT block to do its magic, it doesn't work in persistent environments that don't execute INIT blocks, such as in mod_perl. The specification rules differ slightly from those of Class::Delegation, so this module isn't a drop-in replacement for Class::Delegation. Read on for details.

Specifying methods to be delegated

The names of methods to be redispatched can be specified using the send parameter. This parameter may be specified as a single string or as an array of strings. A single string specifies a single method to be delegated, while an array reference is a list of methods to be delegated.

Specifying attributes to be delegated to

Use the to parameter to specify the attribute or method to which the methods specified by the send parameter are to be delegated. The semantics of the to parameter are a bit different from Class::Delegation. In order to ensure the fastest performance possible, this module simply installs methods into the calling class to handle the delegation. There is no use of $AUTOLOAD or other such trickery. But since the new methods are installed by evaling a string, the to parameter for each delegation statement must be specified in the manner appropriate to accessing the underlying attribute. For example, to delegate a method call to an attribute stored in a hash key, simply wrap the key in braces:

  use Class::Delegator
      send => 'start',
      to   => '{engine}',
  ;

To delegate to a method, simply name the method:

  use Class::Delegator
      send => 'power',
      to   => 'flywheel',
  ;

If your objects are array-based, wrap the appropriate array index number in brackets:

  use Class::Delegator
      send => 'idle',
      to   => '[3]',
  ;

And so on.

Specifying the name of a delegated method

Sometimes it's necessary for the name of the method that's being delegated to be different from the name of the method to which you're delegating execution. For example, your class might already have a method with the same name as the method to which you're delegating. The as parameter allows you translate the method name or names in a delegation statement. The value associated with an as parameter specifies the name of the method to be invoked, and may be a string or an array (with the number of elements in the array matching the number of elements in a corresponding send array).

If the attribute is specified via a single string, that string is taken as the name of the attribute to which the associated method (or methods) should be delegated. For example, to delegate invocations of $self->power(...) to $self->{flywheel}->power(...):

  use Class::Delegator
      send => 'power',
      to   => '{flywheel}',
      as   => 'brake',
  ;

If both the send and the as parameters specify array references, each local method name and deleted method name form a pair, which is invoked. For example:

  use Class::Delegator
      send => [qw(accelerate decelerate)],
      to   => 'brakes',
      as   => [qw(start stop)],
  ;

In this example, the accelerate method will be delegated to the start method of the <brakes> attribute and the decelerate method will be delegated to the stop method of the brakes attribute.

Bugs

Please send bug reports to <bug-class-delegator@rt.cpan.org>.

Author

David Wheeler <david@kineticode.com>

Copyright and License

Copyright (c) 2005 Kineticode, Inc. All Rights Reserved.

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