revisit primitive data types

Original Issue

Revisit the current list of primitive data types to be complete and ensure they map well to http://phpcr.github.com/doc/html/phpcr/propertytype.html

We decided at DrupalCon that we should mark all data types with appropriate constants. The constants would live in a separate class Drupal\Core\TypedData\DataPrimitive.

So hook_data_type_info() would work something like this:

use Drupal\Core\TypedData;

/**
 * Implements hook_data_type_info().
 */
function system_data_type_info() {
  return array(
    'string' => array(
      /* ... */
      'primitive type' => DataPrimitive::TYPE_STRING,
    ),
  );
}

Proposed solution

The TypedData API data model consists of data lists, data structures and data primitives, whereas a list is a sequential list of data and a structure contains any number of data properties. Data definitions describe data based upon defined data types, which are primitives and any module added data type (as e.g. a field type or an entity). Added data types may be mapped to the built-in primitives which are predefined, e.g. an e-mail type would be mapped to the string primitive (but could add further validation logic). This allows modules to operate with any kind of typed data just by supporting data structures, data lists and the built-in primitives.

Built-in primitive data types

Data definitions relate to a class which may be used to wrap and work with the data value based upon the DataWrapperInterface. Further typed data wrappers can be derived from objects implementing the DataStructureInterface or the DataListInterface.