Moose->unimport has to be caled as a method for the into_level stuff to work

[gitmo/Moose.git] / lib / Moose / Cookbook / Extending / Recipe2.pod

=pod

=head1 NAME

Moose::Cookbook::Extending::Recipe2 - Acting like Moose.pm and providing sugar Moose-style

=head1 SYNOPSIS

  package MyApp::Mooseish;

  use strict;
  use warnings;

  our @EXPORT = qw( has_table );

  use base 'Exporter';
  use Class::MOP;
  use Moose ();

  sub import {
    my $caller = caller();

    return if $caller eq 'main';

    Moose::init_meta( $caller,
                      undef, # object base class
                      'MyApp::Meta::Class',
                    );

    Moose->import( { into => $caller }, @_ );

    __PACKAGE__->export_to_level( 1, @_ );
  }

  sub unimport {
      my $caller = caller();

      Moose::remove_keywords(
          source   => __PACKAGE__,
          package  => $caller,
          keywords => \@EXPORT,
      );

      Moose->unimport( { into_level => 1 } );
  }

  sub has_table {
      my $caller = caller();

      $caller->meta()->table(shift);
  }

=head1 DESCRIPTION

The code above shows what it takes to provide an import-based
interface just like C<Moose.pm>. This recipe builds on
L<Moose::Cookbook::Extending::Recipe1>. Instead of providing our own
object base class, we provide our own metaclass class, and we also
export a sugar subroutine C<has_table()>.

Given the above code, you can now replace all instances of C<use
Moose> with C<use MyApp::Mooseish>. Similarly, C<no Moose> is now
replaced with C<no MyApp::Mooseish>.

=head1 WARNING

This recipe covers a fairly undocumented and ugly part of Moose, and
the techniques described here may be deprecated in a future
release. If this happens, there will be plenty of warning, as a number
of C<MooseX> modules on CPAN already use these techniques.

=head1 HOW IT IS USED

The purpose of all this code is to provide a Moose-like
interface. Here's what it would look like in actual use:

  package MyApp::User;

  use MyApp::Mooseish;

  has_table 'User';

  has 'username';
  has 'password';

  sub login { ... }

  no MyApp::Mooseish;

All of the normal Moose sugar (C<has()>, C<with()>, etc) is available
when you C<use MyApp::Mooseish>.

=head1 DISSECTION

The first bit of magic is the call to C<Moose::init_meta()>. What this
does is create a metaclass for the specified class. Normally, this is
called by C<Moose.pm> in its own C<import()> method. However, we can
call it first in order to provide an alternate metaclass class. We
could also provide an alternate base object class to replace
C<Moose::Object> (see L<Moose::Cookbook::Extending::Recipe1> for an
example).

The C<Moose::init_meta()> call takes three parameters. The first is
the class for which we are initializing a metaclass object. The second
is the base object, which is L<Moose::Object> by default. The third
argument is the metaclass class, which is C<Moose::Meta::Class> by
default.

The next bit of magic is this:

  Moose->import( { into => $caller } );

This use of "into" is actually part of the C<Sub::Exporter> API, which
C<Moose.pm> uses internally to export things like C<has()> and
C<extends()>.

Finally, we call C<< __PACKAGE__->export_to_level() >>. This method
actually comes from C<Exporter>.

This is all a bit fragile since it doesn't stack terribly well. You
can basically only have one Moose-alike module. This may be fixed in
the still-notional C<MooseX::Exporter> module someday.

The C<unimport()> subroutine calls the C<remove_keywords> function
from Moose.  This function removes only the keywords exported by
this module. More precisely, C<remove_keywords> removes from the
C<package> package the keywords given by the C<keywords> argument
that were created in the C<source> package.

Finally, we have our C<has_table()> subroutine. This provides a bit of
sugar that looks a lot like C<has()>.

=head1 AUTHOR

Dave Rolsky E<lt>autarch@urth.orgE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright 2006-2008 by Infinity Interactive, Inc.

L<http://www.iinteractive.com>

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

=pod