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 import.

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 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 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.

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

make_variant_package_name¶

  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

  Some::Variant::Package::_Variant_A003

will be created for you.

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.

build_variant¶

  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.

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.

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);