Refactoring: Refactorings/Replace Dynamic Receptor with Dynamic Method Definition

Classes that use method_missing errors are difficult to debug, so use a dynamic method definition to define the necessary methods.

Mechanics

1. Dynamically define the necessary methods
2. Test
3. Remove method_missing
4. Test

Example: Dynamic Delegation

Before

If a method is not defined in subject, then error messages can become cryptic.

class Decorator
  def initialize(subject)
    @subject = subject
  end

  def method_missing(sym, *args, &block)
    @subject.send sym, *args, &block
  end
end

After

class Decorator
  def initialize(subject)
    subject.public_methods(false).each do |method|
      (class << self; self; end).class_eval do
        define method method do |*args|
          subject.send method, *args
        end
      end
    end
  end
end

Example: User-Defined Data

Before

class Person
  attr_reader :name, age

  def method_missing(sym, *args, &block)
    empty?(sym.to_s.sub(/^empty_/,"").chomp("?"))
  end

  def empty?(sym)
    self.send(sym).nil?
  end
end

After

class Person
  def self.attrs_with_empty_predicate(*args)
    attr_accessor *args

    args.each do |attribute|
      define_method "empty_#{attribute}?" do
        self.send(attribute).nil?
      end
    end
  end

  attrs_with_empty_predicate :name, :age
end