Provided by: libpackage-variant-perl_1.001004-1_all 
NAME
Package::Variant - Parameterizable packages
SYNOPSIS
# declaring a variable Moo role
package My::Role::ObjectAttr;
use strictures 1;
use Package::Variant
# what modules to 'use'
importing => ['Moo::Role'],
# proxied subroutines
subs => [ qw(has around before after with) ],
sub make_variant {
my ($class, $target_package, %arguments) = @_;
# access arguments
my $name = $arguments{name};
# use proxied 'has' to add an attribute
has $name => (is => 'lazy');
# install a builder method
install "_build_${name}" => sub {
return $arguments{class}->new;
};
}
# using the role
package My::Class::WithObjectAttr;
use strictures 1;
use Moo;
use My::Role::ObjectAttr;
with ObjectAttr(name => 'some_obj', class => 'Some::Class');
# using our class
my $obj = My::Class::WithObjectAttr->new;
$obj->some_obj; # returns a Some::Class instance
DESCRIPTION
This module allows you to build packages that return different variations depending on what parameters
are given.
Users of your package will receive a subroutine able to take parameters and return the name of a suitable
variant package. The implmenetation does not care about what kind of package it builds.
Declaring a variable package
There are two important parts to creating a variable package. You first have to give "Package::Variant"
some basic information about what kind of package you want to provide, and how. The second part is
implementing a method receiving the user's arguments and generating your variants.
Setting up the environment for building variations
When you "use Package::Variant", you pass along some arguments that describe how you intend to build your
variations.
use Package::Variant
importing => { $package => \@import_arguments, ... },
subs => [ @proxied_subroutine_names ];
The "importing" option needs to be a hash or array reference with package names to be "use"d as keys, and
array references containing the import arguments as values. These packages will be imported into every
new variant, and need to set up every declarative subroutine you require to build your variable package.
The next option will allow you to use these functions. See "importing" for more options. You can omit
empty import argument lists when passing an array reference.
The "subs" option is an array reference of subroutine names that are exported by the packages specified
with "importing". These subroutines will be proxied from your declaration package to the variant to be
generated.
With "importing" initializing your package and "subs" declaring what subroutines you want to use to build
a variant, you can now write a "make_variant" method building your variants.
Declaring a method to produce variants
Every time a user requests a new variant a method named "make_variant" will be called with the name of
the target package and the arguments from the user.
It can then use the proxied subroutines declared with "subs" to customize the new package. An "install"
subroutine is exported as well allowing you to dynamically install methods into the new package. If these
options aren't flexible enough, you can use the passed name of the new package to do any other kind of
customizations.
sub make_variant {
my ($class, $target, @arguments) = @_;
# ...
# customization goes here
# ...
}
When the method is finished, the user will receive the name of the new package variant you just set up.
Using variable packages
After your variable package is created your users can get a variant generating subroutine by simply
importing your package.
use My::Variant;
my $new_variant_package = Variant(@variant_arguments);
The package is now fully initialized and used. You can import the subroutine under a different name by
specifying an "as" argument.
Dynamic creation of variant packages
For regular uses, the normal import provides more than enough flexibility. However, if you want to create
variations of dynamically determined packages, you can use the "build_variant_of" method.
You can use this to create variations of other packages and pass arguments on to them to allow more
modular and extensible variations.
OPTIONS
These are the options that can be passed when importing "Package::Variant". They describe the environment
in which the variants are created.
use Package::Variant
importing => { $package => \@import_arguments, ... },
subs => [ @proxied_subroutines ];
importing
This option is a hash reference mapping package names to array references containing import arguments.
The packages will be imported with the given arguments by every variation before the "make_variant"
method is asked to create the package (this is done using Import::Into).
If import order is important to you, you can also pass the "importing" arguments as a flat array
reference:
use Package::Variant
importing => [ 'PackageA', 'PackageB' ];
# same as
use Package::Variant
importing => [ 'PackageA' => [], 'PackageB' => [] ];
# or
use Package::Variant
importing => { 'PackageA' => [], 'PackageB' => [] };
The import method will be called even if the list of import arguments is empty or not specified,
If you just want to import a single package's default exports, you can also pass a string instead:
use Package::Variant importing => 'Package';
subs
An array reference of strings listing the names of subroutines that should be proxied. These subroutines
are expected to be installed into the new variant package by the modules imported with "importing".
Subroutines with the same name will be availabe in your declaration package, and will proxy through to
the newly created package when used within "make_variant".
VARIABLE PACKAGE METHODS
These are methods on the variable package you declare when you import "Package::Variant".
make_variant
Some::Variant::Package->make_variant( $target, @arguments );
You need to provide this method. This method will be called for every new variant of your package. This
method should use the subroutines declared in "subs" to customize the new variant package.
This is a class method receiving the $target package and the @arguments defining the requested variant.
import
use Some::Variant::Package;
my $variant_package = Package( @arguments );
This method is provided for you. It will allow a user to "use" your package and receive a subroutine
taking @arguments defining the variant and returning the name of the newly created variant package.
The following options can be specified when importing:
• as
use Some::Variant::Package as => 'Foo';
my $variant_package = Foo(@arguments);
Exports the generator subroutine under a different name than the default.
Package::Variant" METHODS
These methods are available on "Package::Variant" itself.
build_variant_of
my $variant_package = Package::Variant
->build_variant_of($variable_package, @arguments);
This is the dynamic method of creating new variants. It takes the $variable_package, which is a pre-
declared variable package, and a set of @arguments passed to the package to generate a new
$variant_package, which will be returned.
import
use Package::Variant @options;
Sets up the environment in which you declare the variants of your packages. See "OPTIONS" for details on
the available options and "EXPORTS" for a list of exported subroutines.
EXPORTS
Additionally to the proxies for subroutines provided in "subs", the following exports will be available
in your variable package:
install
install($method_name, $code_reference);
Installs a method with the given $method_name into the newly created variant package. The $code_reference
will be used as the body for the method, and if Sub::Name is available the coderef will be named. If you
want to name it something else, then use:
install($method_name, $name_to_use, $code_reference);
AUTHOR
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
CONTRIBUTORS
phaylon - Robert Sedlacek (cpan:PHAYLON) <r.sedlacek@shadowcat.co.uk>
COPYRIGHT
Copyright (c) 2010-2012 the "Package::Variant" "AUTHOR" and "CONTRIBUTORS" as listed above.
LICENSE
This library is free software and may be distributed under the same terms as perl itself.
perl v5.14.2 2013-05-04 Package::Variant(3pm)