Class: DCI::Role

Inherits:

Object

• Object
• DCI::Role

Defined in:

lib/dci/role.rb

Overview

Interaction - The Interaction is “what the system does.” The Interaction is implemented as Roles which are played by objects at run time. These objects combine the state and methods of a Data (domain) object with methods (but no state, as Roles are stateless) from one or more Roles. In good DCI style, a Role addresses another object only in terms of its (methodless) Role. There is a special Role called ‘@self` which binds to the object playing the current Role. Code within a Role method may invoke a method on `@self` and thereby invoke a method of the Data part of the current object. One curious aspect of DCI is that these bindings are guaranteed to be in place only at run time (using a variety of approaches and conventions; C++ templates can be used to guarantee that the bindings will succeed). This means that Interactions—the Role methods—are generic. In fact, some DCI implementations use generics or templates for Roles.

A Role is a stateless programming construct that corresponds to the end user’s mental model of some entity in the system. A Role represents a collection of responsibilities. Whereas vernacular object-oriented programming speaks of objects or classes as the loci of responsibilities, DCI ascribes them to Roles. An object participating in a use case has responsibilities: those that it takes on as a result of playing a particular Role.

In the money transfer use case, for example, the role methods in the SourceAccount and DestinationAccount enact the actual transfer.

class Account::TransferWithdraw < Role
  def transfer(amount)
    decrease_balance(amount)
    log "Tranfered from account #{account_id} $#{amount}"
  end
end

class Account::TransferDepoit < Role
  def transfer(amount)
    increase_balance(amount)
    log "Tranfered into account #{account_id} $#{amount}"
  end
end

Instance Method Summary

• #initialize(player) ⇒ Role constructor

  A new instance of Role.

• #method_missing(s, *a, &b) ⇒ Object

Constructor Details

#initialize(player) ⇒ Role

Returns a new instance of Role.

# File 'lib/dci/role.rb', line 44

def initialize(player)
  @self = player
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(s, *a, &b) ⇒ Object

TODO:

Should use #public_send?

# File 'lib/dci/role.rb', line 50

def method_missing(s, *a, &b)
  @self.__send__(s, *a, &b)
end