NAME
MooseX::ConstructInstance - small wrapper method for instantiating
helper objects
SYNOPSIS
This role consists of a single method:
sub construct_instance {
my (undef, $class, @args) = @_;
$class->new(@args);
}
DESCRIPTION
Normally you would build an LWP::UserAgent something like this:
sub _build_ua {
my $self = shift;
LWP::UserAgent->new(...);
}
Following the principles of dependency injection, you may prefer not to
hard-code the class name (see also MooseX::RelatedClasses):
has ua_class => (is => 'ro', default => 'LWP::UserAgent');
sub _build_ua {
my $self = shift;
$self->ua_class->new(...);
}
This module allows you to take it to a further level of abstraction:
has ua_class => (is => 'ro', default => 'LWP::UserAgent');
sub _build_ua {
my $self = shift;
$self->construct_instance($self->ua_class, ...);
}
Why? What benefit do we accrue from constructing all our helper objects
via a seemingly redundant object method call? How about this:
{
package Authentication;
use Moose::Role;
around construct_instance => sub {
my ($orig, $self, $class, @args) = @_;
my $instance = $self->$orig($class, @args);
if ($instance->DOES('LWP::UserAgent')) {
$instance->credentials('', '', 'username', 'password');
}
return $instance;
};
}
Moose::Util::ensure_all_roles($something, 'Authentication');
Now whenever $something constructs an LWP::UserAgent object, it will
automatically have authentication credentials supplied.
MooseX::ConstructInstance can be used to apply policies such as:
* If $foo has a "dbh" attribute, and it constructs an object $bar,
then $bar should inherit $foo's database handle.
* All node objects must be have "backlinks" to the parent node that
created them.
Despite the name, MooseX::ConstructInstance is actually a Moo::Role. You
can apply MooseX::ConstructInstance to Moose classes using:
package MyClass;
use Moose;
with qw( MooseX::ConstructInstance );
You can apply it to Moo classes using:
package MyClass;
use Moo;
with qw( MooseX::ConstructInstance );
You can apply it to other classes using:
package MyClass;
use MooseX::ConstructInstance -with;
BUGS
Please report any bugs to
<http://rt.cpan.org/Dist/Display.html?Queue=MooseX-ConstructInstance>.
SEE ALSO
Moose, MooseX::RelatedClasses.
AUTHOR
Toby Inkster <tobyink@cpan.org>.
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.