DCI in Ruby (Role Injection)

dci_in_ruby_role_injection.rb

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

module Context
  include ContextAccessor

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

  def in_context
    old_context = self.context
    self.context = self
    yield
    self.context = old_context
  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 MoneyTransfer
  include Context

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

  attr_reader :source, :destination

  def initialize source, destination
    @source = source.extend SourceAccount
    @destination = destination.extend DestinationAccount
  end

  def transfer_amount amount
    in_context do
      source.transfer_out amount
      save_changes
    end
  end

  private

  def save_changes
    source.save!
    destination.save!
  end


  # Roles
  # ===========================================
  module SourceAccount
    include ContextAccessor

    def transfer_out amount
      decrease_balance amount
      context.destination.deposit amount
    end
  end

  module DestinationAccount
    include ContextAccessor

    def deposit amount
      increase_balance amount
    end
  end
end


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