Catalyst::Delta - Overview of changes between versions of Catalyst


This is an overview of the user-visible changes to Catalyst between major Catalyst releases.

VERSION 5.9XXXX 'cataplack'

The Catalyst::Engine sub-classes have all been removed and deprecated, to be replaced with Plack handlers.

Plack is an implementation of the PSGI specification, which is a standard interface between web servers and application frameworks.

This should be no different for developers, and you should not have to migrate your applications unless you are using a custom engine already.

This change benefits Catalyst significantly by reducing the amount of code inside the framework, and means that the framework gets upstream bug fixes in Plack, and automatically gains support for any web server which a PSGI compliant handler is written for.

It also allows you more flexibility with your application, and allows the use of cross web framework 'middleware'.

Developers are recommended to read Catalyst::Upgrading for notes about upgrading, especially if you are using an unusual deployment method.

Documentation for how to take advantage of PSGI can be found in Catalyst::PSGI, and information about deploying your application has been moved to Catalyst::Manual::Deployment.

Updated modules:

A number of modules have been updated to pass their tests or not produce deprecation warnings with the latest version of Catalyst. It is recommended that you upgrade any of these that you are using after installing this version of Catalyst.

These extensions are:


This is now deprecated, see Catalyst::Upgrading.


Has been updated to not produce deprecation warnings, upgrade recommended.


Has been updated to fix failing tests (although older versions still function perfectly with this version of Catalyst).


Has been updated to fix failing tests (although older versions still function perfectly with this version of Catalyst).


Has been updated to fix failing tests (although older versions still function perfectly with this version of Catalyst).


VERSION 5.8XXXX 'catamoose'


Please see Catalyst::Upgrading for a full description of how changes in the framework may affect your application.

Below is a brief list of features which have been deprecated in this release:

::[MVC]:: style naming scheme has been deprecated and will warn
NEXT is deprecated for all applications and components, use MRO::Compat
Dispatcher methods which are an implementation detail made private, public versions now warn.
MyApp->plugin method is deprecated, use Catalyst::Model::Adaptor instead.
__PACKAGE__->mk_accessors() is supported for backward compatibility only, use Moose attributes instead in new code.
Use of Catalyst::Base now warns

New features


Fix forwarding to Catalyst::Action objects.
Add the dispatch_type method


The development server restarter has been improved to be compatible with immutable Moose classes, and also to optionally use B::Hooks::OP::Check::StashChange to handle more complex application layouts correctly.

$c->uri_for_action method.

Give a private path to the Catalyst action you want to create a URI for.


Log levels have been made additive.


Change to use Sub::Exporter.
Support mocking multiple virtual hosts
New methods like action_ok and action_redirect to write more compact tests


  • New print method which prints @data to the output stream, separated by $,. This lets you pass the response object to functions that want to write to an IO::Handle.

  • Added code method as an alias for $res->status

Consequences of the Moose back end

  • Components are fully compatible with Moose, and all Moose features, such as method modifiers, attributes, roles, BUILD and BUILDARGS methods are fully supported and may be used in components and applications.

  • Many reusable extensions which would previously have been plugins or base classes are better implemented as Moose roles.

  • MooseX::MethodAttributes::Inheritable is used to contain action attributes. This means that attributes are represented in the MOP, and decouples action creation from attributes.

  • There is a reasonable API in Catalyst::Controller for working with and registering actions, allowing a controller sub-class to replace subroutine attributes for action declarations with an alternate syntax.

  • Refactored capturing of $app from Catalyst::Controller into Catalyst::Component::ApplicationAttribute for easier reuse in other components.

  • Your application class is forced to become immutable at the end of compilation.

Bug fixes

  • Don't ignore SIGCHLD while handling requests with the development server, so that system() and other ways of creating child processes work as expected.

  • Fixes for FastCGI when used with IIS 6.0

  • Fix a bug in uri_for which could cause it to generate paths with multiple slashes in them.

  • Fix a bug in Catalyst::Stats, stopping garbage being inserted into the stats if a user calls begin => but no end