MooseX::CascadeClearing - Cascade clearer actions across attributes


This document describes version 0.05 of MooseX::CascadeClearing - released September 15, 2012 as part of MooseX-CascadeClearing.


    use Moose;
    use MooseX::CascadeClearing;

    has master => (
        is              => 'rw',
        isa             => 'Str',
        lazy_build      => 1,
        is_clear_master => 1,

    my @opts => (
        is           => 'ro',
        isa          => 'Str',
        clear_master => 'master',
        lazy_build   => 1,

    has sub1 => @opts;
    has sub2 => @opts;
    has sub3 => @opts;

    sub _build_sub1 { shift->master . "1" }
    sub _build_sub2 { shift->master . "2" }
    sub _build_sub3 { shift->master . "3" }

    sub some_sub {
        # ...

        # clear master, sub[123] in one fell swoop



MooseX::CascadeClearing does the necessary metaclass fiddling to allow an clearing one attribute to be cascaded through to other attributes as well, calling their clear accessors.

The intended purpose of this is to assist in situations where the value of one attribute is derived from the value of another attribute -- say a situation where the secondary value is expensive to derive and is thus lazily built. A change to the primary attribute's value would invalidate the secondary value and as such the secondary should be cleared. While it could be argued that this is trivial to do manually for a few attributes, once we consider subclassing and adding in roles the ability to "auto-clear", as it were, is a valuable trait. (Sorry, couldn't resist.)


We don't yet trigger a cascade clear on a master attribute's value being set through a setter/accessor accessor. This will likely be available as an option in the not-too-distant-future.


We install an attribute metaclass trait that provides two additional attribute options, as well as wraps the generated clearer method for a designated "master" attribute. By default, using this module causes this trait to be installed for all attributes in the package.

is_clear_master => (0|1)

If set to 1, we wrap this attribute's clearer with a sub that looks for other attributes to clear.

clear_master => < attribute_name >

Marks this attribute as one that should be cleared when the named attribute's clearer is called. Note that no checking is done to ensure that the named master is actually an attribute in the class.


The development version is on github at and may be cloned from git://


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


Chris Weyl <>


This software is Copyright (c) 2012 by Chris Weyl.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999