NAME MooseX::ErsatzMethod - provide a method implementation that isn't as good as the real thing SYNOPSIS package Greetable; use Moose::Role; use MooseX::ErsatzMethod; sub greet { my $self = shift; say "Hello ", $self->name; } ersatz name => sub { my $self = shift; return Scalar::Util::refaddr($self); }; package Person; use Moose; with 'Greetable'; has name => (is => 'ro', isa => 'Str'); package Termite; use Moose; with 'Greetable'; # no need to implement 'name'. DESCRIPTION MooseX::ErsatzMethod provides a mechanism for Moose roles to provide fallback implementations of methods that they really want for consuming classes to implement. In the SYNOPSIS section, the "Greetable" role really wants consuming classes to implement a "name" method. The "Termite" class doesn't implement "name", but it's OK, because "Greetable" provides a fallback (albeit rubbish) implementation of the method. But wait! I hear you say. Don't roles already work that way? Can't a role provide an implementation of a method which consuming classes can override? Yes, they can. However, the precedence is: consuming class's implementation (wins) role's implementation inherited implementation (e.g. from parent class) That is, the role's method implementation overrides methods inherited from the parent class. An ersatz method implementation sits right at the bottom of the heirarchy; it is only used if the consuming class and its ancestors cannot provide the method. (It still beats "AUTOLOAD" though.) One other feature of ersatz methods is that they can never introduce role composition conflicts. If you compose two different roles which both provide ersatz method implementations, an arbitrary method implementation is selected. Functions "ersatz $name => $coderef" Defines an ersatz function. Metarole Trait Your metarole (i.e. "$metarole = Greetable->meta") will have the following additional methods: "ersatz_methods" Returns a name => object hashref of ersatz methods for this class. The objects are instances of MooseX::ErsatzMethod::Meta::Method. "all_ersatz_methods" Returns just the values (objects) from the "ersatz_methods" hash. "add_ersatz_method($name, $coderef)" Given a name and coderef, creates a MooseX::ErsatzMethod::Meta::Method object and adds it to the "ersatz_methods" hash. "apply_all_ersatz_methods_to_class($class)" Given a Moose::Meta::Class object, iterates through "all_ersatz_methods" applying each to the class. This procedure skips any ersatz method for which this role can provide a real method. MooseX::ErsatzMethod::Meta::Method Instances of this class represent an ersatz method. "new(%attrs)" Standard Moose constructor. "code" The coderef for the method. "name" The sub name for the method (not including the package). "associated_role" The metarole associated with this method (if any). "apply_to_class($class)" Given a Moose::Meta::Class object, installs this method into the class unless the class (or a superclass) already has a method of that name. CAVEATS with 'Role1'; with 'Role2'; # No! with qw( Role1 Role2 ); # Yes BUGS Please report any bugs to . SEE ALSO Moose::Role. . AUTHOR Toby Inkster . COPYRIGHT AND LICENCE This software is copyright (c) 2012 by Toby Inkster. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. DISCLAIMER OF WARRANTIES THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.