# PODNAME: Bread::Board::Manual::Concepts::Advanced
# ABSTRACT: An overview of some of the more advanced Bread::Board concepts

__END__

=pod

=head1 NAME

Bread::Board::Manual::Concepts::Advanced - An overview of some of the more advanced Bread::Board concepts

=head1 VERSION

version 0.30

=head1 INTRODUCTION

In the L<Bread::Board::Manual::Concepts> document we attempted to
explain the conceptual foundations of Bread::Board. In that we exposed
you to the idea of a container and a service and showed how they
could be used. In that document we built a hierarchal container
which organized different sets of services into what could be seen
as subsystems within an overall application. While this alone has
plenty of value, you might be asking yourself, what about re-use?
Bread::Board already encourages decoupled object design by removing
the need to manually wire your application components together, but
what about re-using Bread::Board components themselves?

This document will illustrate some of the more advanced concepts in
Bread::Board with the specific focus on re-use and extension.

=head1 ADVANCED CONCEPTS

NOTE: This is just a quick sketch of these docs, more to come in the
next few releases, for now I need to get this one out the door.

=head2 Subclassing

Bread::Board was built from the very start to be an open system and
to allow for the subclassing of all its internal components.

Here is a simple example of extending L<Bread::Board::Container> to
build a container specific to your application.

  package My::Application::Container;
  use Moose;
  use Bread::Board;

  extends 'Bread::Board::Container';

  has 'log_file_name' => (
      is      => 'ro',
      isa     => 'Str',
      default => 'logfile.log',
  );

  sub BUILD {
      my $self = shift;
      container $self => as {

          service 'log_file' => $self->log_file_name;

          service 'logger' => (
              class        => 'My::FileLogger',
              lifecycle    => 'Singleton',
              dependencies => {
                  log_file => depends_on('log_file'),
              }
          );

          service 'application' => (
              class        => 'My::Application',
              dependencies => {
                  logger => depends_on('logger'),
              }
          );
      };
  }

Then you can simply create an instance of the container
and instantiate an instance of the application.

  my $c = My::Application::Container->new(
      name          => 'MyLoggingContainer',
      log_file_name => 'other_logfile.log'
  );

  my $app = $c->resolve( service => 'application');

It should be noted that when calling the constructor of a
subclass of Bread::Board::Container, you must pass the "name"
attribute as a parameter. Additionally you could use the
C<+name> syntax in the subclass itself like so:

  has '+name' => ( default => 'MyLoggingContainer' );

which will remove the requirement in the constructor unless
you choose to override it.

It is also possible to extend/specialize a
L<Bread::Board::Service> type to customize it for your
needs.

More to come later.

=head2 Parameterized Containers

Extending containers is just one form of re-use, just like
extending a class in plain old OOP. But Bread::Board also
provides another means of re-use, and that is parameterized
containers.

If you are familiar with functors in Standard ML or O'Caml
then this might look familiar to you. A parameterized
container is basically a container which expects another
container (or containers) as an argument and produces a
third container as the result.

Lets take a simple example here of a Logger object which
logs to a database.

  my $db_logger = container 'DatabaseLogger' => [ 'DBConnInfo' ] => as {
      service 'handle' => (
          class        => 'My::Database::Logger',
          dependencies => {
              dsn      => depends_on('DBConnInfo/dsn'),
              username => depends_on('DBConnInfo/username'),
              password => depends_on('DBConnInfo/password'),
          }
      );
  };

It is parameterized with a C<DBConnInfo> container which has
three services, a C<dsn>, a C<username> and a C<password>.
Now let's create a simple container which fufills these
requirements.

  my $db_conn_info = container 'DatabaseConnection' => as {
      service 'dsn'      => 'dbi:mysql:foo';
      service 'username' => 'bar';
      service 'password' => '***';
  };

The above container fulfills the bare minimum, but this could have
just as easily have been a much more complex container which
also had a service for a L<DBIx::Class> schema, or a L<KiokuDB>
directory object. As long as the container provided the
three required services, that was all that the C<DatabaseLogger>
parameterized container required.

Now, a parameterized container is not a usable container, you
must create an instance of it. That is as simple as calling the
C<create> method, like so.

  my $my_db_logger = $db_logger->create(
      DBConnInfo => $db_conn_info
  );

After which you can use it just like any other Bread::Board
container would be used.

  my $log_handle = $my_db_logger->resolve(
      service => 'handle'
  );

Parameterized containers can also be nested, here is an example
of an Application container that expects a Logger.

  my $app = container 'Application' => [ 'Logger' ] => as {
      service 'app' => (
          class        => 'My::Application',
          dependencies => {
              log_handle => depends_on('Logger/handle')
          }
      );
  };

And here we instantiate an instance of our Application container
using the DatabaseLogger.

  my $db_app = $app->create(
      Logger => $db_logger->create(
          DBConnInfo => $db_conn_info
      )
  );

And of course, since the Logger is a parameter we could just as
easily pass in a simpler screen logger for a test environment or
something. Here is what that would look like.

  my $simple_logger = container 'SimpleLogger' => as {
      service 'handle' => (
          class => 'My::Simple::Logger'
      );
  };

  my $simple_app = $app->create(
      Logger => $simple_logger
  );

Parameterized containers provide a useful and powerful means
of re-use and abstraction, making it easy to create flexible
containers to model your applications subsystems.

=head1 AUTHOR

Stevan Little <stevan@iinteractive.com>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Infinity Interactive.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
