Refactoring: Refactorings/Isolate Dynamic Receptor

A class that uses method_missing can become painful to alter. method_missing is a powerful tool that provides a lot of options, but if incorrectly placed, it can be difficult to determine which class is responsible for what methods.

Solution: introduce a new class and move the method_missing logic to that class.

Mechanics

1. Create a new class whose sole responsibility is to handle the dynamic method calls
2. Copy the logic from method_missing on the original class to the method_missing of the focused class
3. Create a method on the original class to return an instance of the focused class
4. Change all client code that previously called the dynamic methods on the original object to call the new method first
5. Remove the method_missing from the original object
6. Test

Example

class Recorder
  instance_methods.each do |meth|
    undef_method meth unless meth =~ /^(__|inspect)/
  end

  def messages
    @messages ||= []
  end

  def method_missing(sym, *args)
    messages << [sym, args]
    self
  end

  def play_for(obj)
    messages.inject(obj) do |result, message|
      result.send message.first, *message.last
    end
  end

  def to_s
    messages.inject([]) do |result, message|
      result << "#{message.first}(args: #{message.last.inspect})"
    end.join(".")
  end
end

class CommandCenter
  def start(command_string)
    # ...
    self
  end

  def stop(command_string)
    # ...
    self
  end
end

Recorder = Recorder.new
recorder.start("LRMMMMRL")
recorder.stop("LRMMMMRL")
recorder.play_for(CommandCenter.new)

After

class MessageCollector
  instance_methods.each do |meth|
    undef_method meth unless meth =~ /^(__|inspect)/
  end

  def messages
    @messages ||= []
  end

  def method_missing(sym, *args)
    messages << [sym, args]
    self
  end
end

class Recorder
  def play_for(obj)
    @message_collector.messages.inject(obj) do |result, message|
      result.send message.first, *message.last
    end
  end

  def record
    @message_collector ||= MessageCollector.new
  end

  def to_s
    @message_collector.messages.inject([]) do |result, message|
      result << "#{message.first}(args: #{message.last.inspect})"
    end.join(".")
  end
end

class CommandCenter
  def start(command_string)
    # ...
    self
  end

  def stop(command_string)
    # ...
    self
  end
end

recorder = Recorder.new
recorder.record.start("LRMMMMRL")
recorder.record.stop("LRMMMMRL")
recorder.play_for(CommandCenter.new)