DCI in Ruby (No Role Injection)

dci_in_ruby_without_injection.rb

# Framework
# ===========================================
module ContextAccessor
  def context
    Thread.current[:context]
  end
end

module Context
  include ContextAccessor

  attr_reader :role_player

  def context=(ctx)
    Thread.current[:context] = ctx
  end

  def in_context
    old_context = self.context
    self.context = self
    return_object = yield
    self.context = old_context
    return_object
  end

  def roles map
    @role_player = map
  end
end

module Role
  include ContextAccessor
  extend self

  def included clazz
    clazz.extend clazz
  end

  protected

  def player
    raise "No active   context" unless context
    res = context.role_player[self]
    raise "No object playing the role #{self}" unless res
    res
  end

  def method_missing(method, *args, &block)
    player.send(method, *args, &block)
  end
end


# Data
# ===========================================
class Account
  attr_reader :balance

  def initialize balance
    @balance = balance
  end

  @accounts = {1 => Account.new(100), 2 => Account.new(200)}

  def self.find id
    @accounts[id]
  end

  def increase_balance amount
    @balance += amount
  end

  def decrease_balance amount
    @balance -= amount
  end

  def save!
  end
end


# Context
# ===========================================
class MoneyTransfer2
  include Context

  def self.transfer source_account_id, dest_account_id, amount
    source = Account.find(source_account_id)
    dest = Account.find(dest_account_id)
    MoneyTransfer2.new(source, dest).transfer_amount(amount)
  end

  def initialize source, destination
    roles SourceAccount      => source,
          DestinationAccount => destination
  end

  def transfer_amount amount
    in_context do
      SourceAccount.transfer amount
      save_objects
    end
  end

  def save_objects
    SourceAccount.save!
    DestinationAccount.save!
  end

  module SourceAccount
    include Role

    def transfer amount
      DestinationAccount.deposit amount
      SourceAccount.withdraw amount
    end

    def withdraw amount
      decrease_balance amount
    end
  end

  module DestinationAccount
    include Role

    def deposit amount
      increase_balance amount
    end
  end
end

#MoneyTransfer2.transfer 1, 2, 50
#p Account.find(1).balance
#p Account.find(2).balance