Delegation is a design pattern and a concept in software engineering where an object handles a request by passing it to a second “delegate” object. The delegate object is responsible for performing the actual task. This pattern is used to achieve separation of concerns and to promote code reuse and flexibility.

Key Points

• Separation of Concerns: Delegation helps in separating the responsibilities of different objects, making the code more modular and easier to maintain.
• Code Reuse: By delegating tasks to other objects, you can reuse existing code and avoid duplication.
• Flexibility Delegation allows you to change the behavior of an object at runtime by changing its delegate.

Example in Ruby

In Ruby, delegation can be achieved using the Forwardable module or the delegate method.

Using Forwardable Module

require 'forwardable'

class Printer
  def print_message(message)
    puts message
  end
end

class Document
  extend Forwardable
  def_delegators :@printer, :print_message

  def initialize
    @printer = Printer.new
  end
end

doc = Document.new
doc.print_message("Hello, World!") # Output: Hello, World!

Using delegate Method

require 'delegate'

class Printer
  def print_message(message)
    puts message
  end
end

class Document < SimpleDelegator
  def initialize
    super(Printer.new)
  end
end

doc = Document.new
doc.print_message("Hello, World!") # Output: Hello, World!

doc = Document.new

Summary

Delegation is a design pattern that allows an object to pass a request to a delegate object to handle the actual task. It promotes separation of concerns, code reuse, and flexibility in software design.