Chapter 17. Root software elements (RSEs)

Chapter 17. Root software elements (RSEs)
	Part III. Language reference

Table of Contents

Type
Factory
Service

Type

	Note
	This chapter only describes basic concepts of types. Please have a look at the links at the end of this section to get information about more advanced features (e.g. type inheritance and generic types).

Description

Types are used to describe features of objects.

There are 3 different kinds of features:

attributes
commands
events

Each type can contain 0, 1 or or more features of each kind.

Each type is identified by a unique type identifier. A type identifier is a prefixed identifier starting with ty_ as prefix. For more information about prefixed identifiers see the section called “Prefixed identifier”.

Types cannot be used to create objects. Objects can only be created by factories (see the section called “Factory”). 0, 1 or or more objects of a given type can exist at a given point of time.

Each type implicitly inherits from type any_type which is the parent type of each type in the type system. Type any_type is defined as follows:

///
   Copyright (C) 2009-2012 Christian Neumanns (www.rps-obix.com)
   This code can be used under the terms of the 'GNU Afero General Public License version 3'
   The full text of this license can be found at http://www.gnu.org/licenses/agpl.html
   THIS CODE IS DISTRIBUTED WITHOUT ANY WARRANTY. See the license for details.
end ///

type any_type

   command to_string
      out result type:string end
   end

end type

Syntax

Table 17.1. Type

Production	Syntax	Links
`type`	`"type" ( "id" ":" ) ? type_id ( "default_factory" ":" ( "yes" \| "no" ) ) ? RSE_java_code ? inherited_type_list ? attribute_list ? attribute_list_check ? command_list ? event_list ? RSE_test_script ? "end" "type" ?`	the section called “Type”

A type is quite often used to simply define a structure of data, that is to say objects without any behavior. Such types contain only attributes, no commands and no events. The implementation of such types often consists of a factory with all attributes implemented as objects in memory, and a creator with one input argument for each attribute. As it would be tedious to code such factories again and again, the clause default_factory:yes tells the compiler to automatically create such a factory. In this case, the factory's id suffix is the same as the type's id suffix. See example below.

Examples

Example 17.1. Simple dog

First, a very simple example of a type with one attribute and one command

type dog
   attribute name type:string end
   command bark end
end type

Example 17.2. Type customer

The following is a simple type with 4 attributes. It also declares a default factory.

type customer default_factory:yes
   attribute identifier type:positive32 end
   attribute name type:string kind:variable end              // value can be changed after an object's creation
   attribute city type:string voidable:yes kind:variable end // value can be void
   attribute is_company type:yes_no default:no end           // default value is no 
end type

default_factory:yes in the above example tells the compiler to automatically create the following factory, so we don't have to create it manually if the default implementation suits our needs:

factory customer type: customer

   attribute identifier end
   attribute name end
   attribute city end
   attribute is_company end

   creator create
      in identifier type:positive32 end
      in name type:string end
      in city type:string voidable:yes end
      in is_company type:yes_no default:no end

      out result type:customer end

      script
         o_result.a_identifier = i_identifier
         o_result.a_name = i_name
         o_result.a_city = i_city
         o_result.a_is_company = i_is_company
      end script 
   end creator 
end factory

A customer can be created as follows:

var customer my_customer = fa_customer.co_create ( &
   identifier = 123 &
   name = "Albert Newton" &
   city = void )

As we didn't specify a value for attribute is_company in the above instruction, the value of that attribute will be no, which is the default value defined in type customer.

Example 17.3. Type coffee machine

This example shows a type coffee_machine that uses other types (cup_of_coffee, coffee_machine_switched_on_event, and coffee_machine_switched_off_event) which are not part of Obix's standard library.

type coffee_machine

   attribute switched_on type:yes_no kind:readonly_variable end // is machine on or off?

   command power_on end // turn machine on

   command power_off end // turn machine off

   command make_coffee
      in with_milk type:yes_no default:yes end
      in with_sugar type:yes_no default:no end
      in_check check: object_.switched_on end // machine must be switched on before making coffee

      out result type:cup_of_coffee end
   end command

   event switched_on type: coffee_machine_switched_on_event end // event fired whenever coffee machine is switched on
   event switched_off type: coffee_machine_switched_off_event end // event fired whenever coffee machine is switched off

end type

type cup_of_coffee
   attribute is_empty type:yes_no kind:readonly_variable end
   command drink end // a command with no input and no output arguments
end type

type coffee_machine_state_changed_event

   inherit object_event end

   attribute date_time type:local_date_time end

end type

type coffee_machine_switched_on_event default_factory:yes
   inherit coffee_machine_state_changed_event end
end type

type coffee_machine_switched_off_event default_factory:yes
   inherit coffee_machine_state_changed_event end
end type

For more examples see Chapter 3, Simple example or have a look at the examples found in the links below


Void literal		Factory