Command en Ruby

Command es un patrón de diseño de comportamiento que convierte solicitudes u operaciones simples en objetos.

La conversión permite la ejecución diferida de comandos, el almacenamiento del historial de comandos, etc.

Complejidad:

Popularidad:

Ejemplos de uso: El patrón Command es muy común en el código Ruby. La mayoría de las veces se utiliza como alternativa a las retrollamadas (callbacks) para parametrizar elementos UI con acciones. También se utiliza para poner tareas en cola, realizar el seguimiento del historial de operaciones, etc.

Identificación: El patrón Command es reconocible por los métodos de comportamiento en un tipo de clase abstracta/interfaz (emisora) que invoca un método en una implementación de un tipo de clase abstracta/interfaz diferente (receptora) que la implementación del comando ha implementado durante su creación. Las clases de comando se limitan normalmente a acciones específicas.

Ejemplo conceptual

Este ejemplo ilustra la estructura del patrón de diseño Command. Se centra en responder las siguientes preguntas:

¿De qué clases se compone?
¿Qué papeles juegan esas clases?
¿De qué forma se relacionan los elementos del patrón?

main.rb: Ejemplo conceptual

# The Command interface declares a method for executing a command.
class Command
  # @abstract
  def execute
    raise NotImplementedError, "#{self.class} has not implemented method '#{__method__}'"
  end
end

# Some commands can implement simple operations on their own.
class SimpleCommand < Command
  # @param [String] payload
  def initialize(payload)
    @payload = payload
  end

  def execute
    puts "SimpleCommand: See, I can do simple things like printing (#{@payload})"
  end
end

# However, some commands can delegate more complex operations to other objects,
# called "receivers".
class ComplexCommand < Command
  # Complex commands can accept one or several receiver objects along with any
  # context data via the constructor.
  def initialize(receiver, a, b)
    @receiver = receiver
    @a = a
    @b = b
  end

  # Commands can delegate to any methods of a receiver.
  def execute
    print 'ComplexCommand: Complex stuff should be done by a receiver object'
    @receiver.do_something(@a)
    @receiver.do_something_else(@b)
  end
end

# The Receiver classes contain some important business logic. They know how to
# perform all kinds of operations, associated with carrying out a request. In
# fact, any class may serve as a Receiver.
class Receiver
  # @param [String] a
  def do_something(a)
    print "\nReceiver: Working on (#{a}.)"
  end

  # @param [String] b
  def do_something_else(b)
    print "\nReceiver: Also working on (#{b}.)"
  end
end

# The Invoker is associated with one or several commands. It sends a request to
# the command.
class Invoker
  # Initialize commands.

  # @param [Command] command
  def on_start=(command)
    @on_start = command
  end

  # @param [Command] command
  def on_finish=(command)
    @on_finish = command
  end

  # The Invoker does not depend on concrete command or receiver classes. The
  # Invoker passes a request to a receiver indirectly, by executing a command.
  def do_something_important
    puts 'Invoker: Does anybody want something done before I begin?'
    @on_start.execute if @on_start.is_a? Command

    puts 'Invoker: ...doing something really important...'

    puts 'Invoker: Does anybody want something done after I finish?'
    @on_finish.execute if @on_finish.is_a? Command
  end
end

# The client code can parameterize an invoker with any commands.
invoker = Invoker.new
invoker.on_start = SimpleCommand.new('Say Hi!')
receiver = Receiver.new
invoker.on_finish = ComplexCommand.new(receiver, 'Send email', 'Save report')

invoker.do_something_important

output.txt: Resultado de la ejecución

Invoker: Does anybody want something done before I begin?
SimpleCommand: See, I can do simple things like printing (Say Hi!)
Invoker: ...doing something really important...
Invoker: Does anybody want something done after I finish?
ComplexCommand: Complex stuff should be done by a receiver object
Receiver: Working on (Send email.)
Receiver: Also working on (Save report.)

Command en Ruby

Ejemplo conceptual

main.rb: Ejemplo conceptual

output.txt: Resultado de la ejecución

Command en otros lenguajes