NAME

Form::Tiny::Manual::Internals - details on form implementation

DESCRIPTION

This guide gets in depth into Form::Tiny metaobject model. This knowledge should not be required to make full use of the module, but is required to extend it or contribute to it.

How does the module work?

Behind the scenes, the module stores objects of Form::Tiny::Meta for each package that was turned into a form by a proper Form::Tiny call. Meta object is an object that stores all information about the form layout, but no information about form input or validation state. Each class of Form::Tiny::Form contains the form_meta method, which returns this meta object for the given package.

Form building is done just by calling methods on the meta object. Each helper of the DSL is just a single call to a metaobject method, for example, the following calls are equivalent:

        form_field 'field-name' => %args;
        __PACKAGE__->form_meta->add_field('field-name' => %args);

The actual form object only stores data that is relevant to form state, not to form layout. Thanks to this model, the layout needs not to be rebuilt each time a new form object is constructed, which speeds up construction.

Additional behavior like filtering is implemented by composing new roles to the meta object and declaring new hooks in setup method. Refer to the code of Form::Tiny::Meta::Filtered to see how meta roles may define additional behavior.

Why use meta object model at all?

The 1.00 series of the module did not implement a meta object, and in turn implementing DSL keywords ended up being a hack, abusing Perl's ability to replace symbols in the package with strict mode turned off. New implementation allowed to get rid of all that dark magic, replacing it with something readable and reliable.

Using the module without the syntactic sugar

It is entirely possible, although a bit tedious, to use the module without importing Form::Tiny package. The following example declares a form with a single field taken from the example above.

The code present in metaobject.pl example should result in a form that has the same capabilities as the one below:

        package MyForm;

        use Form::Tiny;

        form_field 'field-name' => (
                required => 1,
        );

        1;

Notice: building your form like this should be done only for educational purposes. Changes in import procedure are not covered by the 3 month deprecation period policy.

Finalizing the meta

After creating the meta object with create_form_meta function, the object exists in an incomplete state. It is so that superclasses can be applied before finalizing the metaobject and applying inheritance. Calling get_package_form_meta will apply all changes needed to achieve complete state.

SEE ALSO

• Form::Tiny::Manual

• Form::Tiny::Manual::Compatibility