Provided by: libpackage-variant-perl_1.003002-1_all bug


       Package::Variant - Parameterizable packages


       Creation of anonymous variants:

         # declaring a variable Moo role
         package My::VariableRole::ObjectAttr;
         use strictures 2;
         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 2;
         use Moo;
         use My::VariableRole::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

       And the same thing, only with named variants:

         # declaring a variable Moo role that can be named
         package My::VariableRole::ObjectAttrNamed;
         use strictures 2;
         use Package::Variant importing => ['Moo::Role'],
           subs => [ qw(has around before after with) ];
         use Module::Runtime 'module_notional_filename'; # only if you need protection

         # this method is run at variant creation time to determine its custom
         # package name. it can use the arguments or do something entirely else.
         sub make_variant_package_name {
           my ($class, $package, %arguments) = @_;
           $package = "Private::$package"; # you can munge the input here if you like
           # only if you *need* protection
           die "Won't clobber $package" if $INC{module_notional_filename $package};
           return $package;

         # same as in the example above, except for the argument list. in this example
         # $package is the user input, and
         # $target_package is the actual package in which the variant gets installed
         sub make_variant {
           my ($class, $target_package, $package, %arguments) = @_;
           my $name = $arguments{name};
           has $name => (is => 'lazy');
           install "_build_${name}" => sub {return $arguments{class}->new};

         # using the role
         package My::Class::WithObjectAttr;
         use strictures 2;
         use Moo;
         use My::VariableRole::ObjectAttrNamed;

         # create the role under a specific name
         ObjectAttrNamed "My::Role" => (name => 'some_obj', class => 'Some::Class');
         # and use it
         with "Private::My::Role";

         # using our class
         my $obj = My::Class::WithObjectAttr->new;
         $obj->some_obj; # returns a Some::Class instance


       This module allows you to build a variable package that contains a package template and
       can use it to build variant packages at runtime.

       Your variable package will export a subroutine which will build a variant package,
       combining its arguments with the template, and return the name of the new variant package.

       The implementation does not care about what kind of packages it builds, be they simple
       function exporters, classes, singletons or something entirely different.

   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 variant packages you want to
       provide, and how. The second part is implementing a method which builds the components of
       the variant packages that use the user's arguments or cannot be provided with a static

       Setting up the environment for building variants

       When you "use Package::Variant", you pass along some arguments that describe how you
       intend to build your variants.

         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 package, to provide static functionality
       of the variant packages and to set up every declarative subroutine you require to build
       variants package components. 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 variable
       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

       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 variant
       package. An "install" subroutine is exported as well allowing you to dynamically install
       methods into the variant package. If these options aren't flexible enough, you can use the
       passed name of the variant 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 variant package you
       just set up.

   Using variable packages
       After your variable package is created your users can get a variant generator subroutine
       by simply importing your package.

         use My::Variant;
         my $new_variant_package = Variant(@variant_arguments);
         # the variant 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 variants of dynamically determined packages, you can use the
       "build_variant_of" method.

       You can use this to create variants of other packages and pass arguments on to them to
       allow more modular and extensible variants.


       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 ];

       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 variant
       before the "make_variant" method is asked to create the package (this is done using

       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

       If you just want to import a single package's default exports, you can also pass a string

         use Package::Variant importing => 'Package';

       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 available in your
       variable package, and will proxy through to the newly created package when used within


       These are methods on the variable package you declare when you import "Package::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.

         Some::Variant::Package->make_variant_package_name( @arguments );

       You may optionally provide this method. If present, this method will be used to determine
       the package name for a particular variant being constructed.

       If you do not implement it, a unique package name something like


       will be created for you.

         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:

       ยท   as

             use Some::Variant::Package as => 'Foo';
             my $variant_package = Foo(@arguments);

           Exports the generator subroutine under a different name than the default.

         use Some::Variant::Package ();
         my $variant_package = Some::Variant::Package->build_variant( @arguments );

       This method is provided for you.  It will generate a variant package and return its name,
       just like the generator sub provided by "import".  This allows you to avoid importing
       anything into the consuming package.

"Package::Variant" METHODS

       These methods are available on "Package::Variant" itself.

         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.

         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.


       Additionally to the proxies for subroutines provided in "subs", the following exports will
       be available in your variable package:

         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);


       mst - Matt S. Trout (cpan:MSTROUT) <>


       phaylon - Robert Sedlacek (cpan:PHAYLON) <>

       haarg - Graham Knop (cpan:HAARG) <>


       Copyright (c) 2010-2012 the "Package::Variant" "AUTHOR" and "CONTRIBUTORS" as listed


       This library is free software and may be distributed under the same terms as perl itself.