Stack Overflow Question #5390537 (http://stackoverflow.com/questions/5390537)

Alex Ds solution r1.rb

## encoding: utf-8
## Alex D's solution (1st revision) to http://stackoverflow.com/questions/5390537/best-practices-and-implementation-for-macro-and-class-level-accessor-methods/9019388#9019388


module MacroMethods
  private
  def full_name(full_name)
    # non-trivial, one-time-only set-up code exists here in actual usage
    self.class_eval { const_set :FULL_NAME, full_name.to_s }
    
    # this method can only be called once in the definition of any given class,
    #   because after the first call, it will be redefined!
    extend AccessorMethods
  end
end

module AccessorMethods
  public
  def full_name
    # a non-trivial, runtime-calculated value is returned here in actual usage
    self::FULL_NAME.upcase
  end
end

class Base
  extend MacroMethods
end

class Something < Base
  full_name 'after this call, I will get a new full_name method!'
end

class SomethingElse < Base
  full_name 'so will I!'
end


puts "Something.full_name: #{Something.full_name}"
puts "SomethingElse.full_name: #{SomethingElse.full_name}"

Alex Ds solution r2.rb

## encoding: utf-8
## Alex D's solution (2nd revision) to http://stackoverflow.com/questions/5390537/best-practices-and-implementation-for-macro-and-class-level-accessor-methods/9019388#9019388


module MacroMethods
  private
  def full_name(full_name)
    # non-trivial, one-time-only set-up code exists here in actual usage
    self.class_eval { const_set :FULL_NAME, full_name.to_s }
    
    # this method can only be called once in the definition of any given class,
    #   because after the first call, it will be redefined!
    define_method(:full_name) do
      # a non-trivial, runtime-calculated value is returned here in actual usage
      self.class.class_eval { self::FULL_NAME.upcase }
    end
  end
end

class Base
  extend MacroMethods
end

class Something < Base
  full_name 'after this call, I will get a new full_name method!'
end

class SomethingElse < Base
  full_name 'so will I!'
end


puts "Something.new.full_name: #{Something.new.full_name}"
puts "SomethingElse.new.full_name: #{SomethingElse.new.full_name}"

Alex Ds solution with class-level accessors.rb

## encoding: utf-8
## Modification of Alex D's solution to http://stackoverflow.com/questions/5390537/best-practices-and-implementation-for-macro-and-class-level-accessor-methods/9019388#9019388


module MacroMethods
  private
  def full_name(full_name)
    # non-trivial, one-time-only set-up code exists here in actual usage
    self.class_eval { const_set :FULL_NAME, full_name.to_s }
    
    # this method can only be called once in the definition of any given class,
    #   because after the first call, it will be redefined!
    self.singleton_class.instance_eval {
      undef_method(:full_name)
      define_method(:full_name) do
        # a non-trivial, runtime-calculated value is returned here in actual usage
        self::FULL_NAME.upcase
      end
      public :full_name
    }
    
    define_method(:full_name) do
      # a non-trivial, runtime-calculated value is returned here in actual usage
      self.class.class_eval { self::FULL_NAME.upcase }
    end
  end
end

class Base
  extend MacroMethods
end

class Something < Base
  full_name 'after this call, I will get a new full_name method!'
end

class SomethingElse < Base
  full_name 'so will I!'
end


puts "Something.new.full_name: #{Something.new.full_name}"
puts "SomethingElse.new.full_name: #{SomethingElse.new.full_name}"
puts "Something.full_name: #{Something.full_name}"
puts "SomethingElse.full_name: #{SomethingElse.full_name}"