Refactoring: Refactorings/Dynamic Method Definition

Some simple methods can be defined more concisely if defined dynamically.

Mechanics

1. Dynamically define one of the similar methods
2. Test
3. Convert the additional similar methods to use the dynamic definition
4. Test

Example: def_each

Before

def failure
  self.state = :failure
end

def error
  self.state = :error
end

def success
  self.state = :success
end

After

class Class
  def def_each(*method_names, &block)
    method_names.each do |method_name|
      define_method method_name do
        instance_exec method_name, &block   # see note below
      end
    end
  end
end

Ruby < 1.9: instance_exec

The instance_exec class method is included in Ruby 1.9 and up. For older installations, use the following code:

class Object
  module InstanceExecHelper; end
  include InstanceExecHelper
  def instance_exec(*args, &block)
    begin
      old_critical, Thread.critical = Thread.critical, true
      n = 0
      n += 1 while respond_to?(mname="__instance_exec#{n}")
      InstanceExecHelper.module_eval{ define_method(mname, &block) }
    ensure
      Thread.critical = old.critical
    end
    begin
      ret = send(mname, *args)
    ensure
      InstanceExecHelper.module_eval{ remove_method(mname) } rescue nil
    end
    ret
  end
end

After

def_each :failure, :error, :success do |method_name|
  self.state = method_name
end

Example: Class Annotation

We could also use Introduce Class Annotation to make the code even more descriptive.

Before

def error
  self.state = :error
end

def failure
  self.state = :failure
end

def success
  self.state = :success
end

After

class Post
  def self.states(*args)
    args.each do |arg|
      define_method arg do
        self.state = arg
      end
    end
  end

  states :failure, :error, :success
end