NAME¶
Moose::Cookbook::Meta::PrivateOrPublic_MethodMetaclass - A method metaclass for
marking methods public or private
VERSION¶
version 2.1213
SYNOPSIS¶
package MyApp::Meta::Method::PrivateOrPublic;
use Moose;
use Moose::Util::TypeConstraints;
extends 'Moose::Meta::Method';
has '_policy' => (
is => 'ro',
isa => enum( [ qw( public private ) ] ),
default => 'public',
init_arg => 'policy',
);
sub new {
my $class = shift;
my %options = @_;
my $self = $class->SUPER::wrap(%options);
$self->{_policy} = $options{policy};
$self->_add_policy_wrapper;
return $self;
}
sub _add_policy_wrapper {
my $self = shift;
return if $self->is_public;
my $name = $self->name;
my $package = $self->package_name;
my $real_body = $self->body;
my $body = sub {
die "The $package\::$name method is private"
unless ( scalar caller() ) eq $package;
goto &{$real_body};
};
$self->{body} = $body;
}
sub is_public { $_[0]->_policy eq 'public' }
sub is_private { $_[0]->_policy eq 'private' }
package MyApp::User;
use Moose;
has 'password' => ( is => 'rw' );
__PACKAGE__->meta()->add_method(
'_reset_password',
MyApp::Meta::Method::PrivateOrPublic->new(
name => '_reset_password',
package_name => __PACKAGE__,
body => sub { $_[0]->password('reset') },
policy => 'private',
)
);
DESCRIPTION¶
This example shows a custom method metaclass that models public versus private
methods. If a method is defined as private, it adds a wrapper around the
method which dies unless it is called from the class where it was defined.
The way the method is added to the class is rather ugly. If we wanted to make
this a real feature, we'd probably want to add some sort of sugar to allow us
to declare private methods, but that is beyond the scope of this recipe. See
the Extending recipes for more on this topic.
The core of our custom class is the "policy" attribute, and
"_add_policy_wrapper" method.
You'll note that we have to explicitly set the "policy" attribute in
our constructor:
$self->{_policy} = $options{policy};
That is necessary because Moose metaclasses do not use the meta API to create
objects. Most Moose classes have a custom "inlined" constructor for
speed.
In this particular case, our parent class's constructor is the "wrap"
method. We call that to build our object, but it does not include
subclass-specific attributes.
The "_add_policy_wrapper" method is where the real work is done. If
the method is private, we construct a wrapper around the real subroutine which
checks that the caller matches the package in which the subroutine was
created.
If they don't match, it dies. If they do match, the real method is called. We
use "goto" so that the wrapper does not show up in the call stack.
Finally, we replace the value of "$self->{body}". This is another
case where we have to do something a bit gross because Moose does not use
Moose for its own implementation.
When we pass this method object to the metaclass's "add_method"
method, it will take the method body and make it available in the class.
Finally, when we retrieve these methods via the introspection API, we can call
the "is_public" and "is_private" methods on them to get
more information about the method.
SUMMARY¶
A custom method metaclass lets us add both behavior and meta-information to
methods. Unfortunately, because the Perl interpreter does not provide easy
hooks into method declaration, the API we have for adding these methods is not
very pretty.
That can be improved with custom Moose-like sugar, or even by using a tool like
Devel::Declare to create full-blown new keywords in Perl.
AUTHORS¶
- •
- Stevan Little <stevan.little@iinteractive.com>
- •
- Dave Rolsky <autarch@urth.org>
- •
- Jesse Luehrs <doy@tozt.net>
- •
- Shawn M Moore <code@sartak.org>
- •
- XXXX XXX'XX (Yuval Kogman) <nothingmuch@woobling.org>
- •
- Karen Etheridge <ether@cpan.org>
- •
- Florian Ragwitz <rafl@debian.org>
- •
- Hans Dieter Pearcey <hdp@weftsoar.net>
- •
- Chris Prather <chris@prather.org>
- •
- Matt S Trout <mst@shadowcat.co.uk>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2006 by Infinity Interactive, Inc..
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.