Question

I’m designing/building a system of classes that all derive from a single base class.

The goal is to have easy-to-use inherited macro methods that look something like this:

class Something < A::Base
  full_name 'Something that goes bump in the night.'
end

Any code should be able to ask the class for this information (or, likely, normalized/derived infomation) later on via class-level accessor method(s).

puts Something.full_name
  # => "Some kind of calculated value that may or may not go bump in the night."

 

Given that A::Base includes/extends/somehow-otherwise-mixes-in both a module with the macro method that works something like this:

module MacroMethods
  private
  def full_name(full_name)
    # non-trivial, one-time-only set-up code exists here in actual usage
  end
end

and a module with the class-level accessor method that works something like this:

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

no matter how I mix them in, I’m continually running into naming conflicts (i.e. ‘wrong number of arguments (1 for 0) (ArgumentError)’) between the two.

Note: full_name is the simplest example of what is needed; other, more-complex macros/accessors ensure the non-flexible constraints of macro methods needing to be declared inside the class and needing to be set once-and-only-once.

---

My question is two-fold:

1. Is there a way to make this all work inside of the A::Base class?
2. Is this the right way to do this in Ruby? Is there a better way go about it, achieving the same result?

Options that have been considered:

• Calling either the macro or accessor method(s) something else.
  (e.g. in Something class: set_up_full_name 'Something that …')
  Downside is that the naming is confusing and unconventional.

• Making the accessor method(s) instance-level instead of class-level.
  (e.g. puts a_something.full_name')
  Downside is that the traits set up by the macros are inherent to the class, not to each instance (in some cases, only a reference to the class may be available, not an instance).

• Creating a single method that handles both macro and accessor functionality.
  (e.g. in A::Base class: def self.full_name(*args) …)
  Downside is that the macro methods can no longer be private and the RDoc looks like sh*t.

• Using abstact/virtual-ish methods instead.
  (e.g. in Something class: def self.full_name; 'Something that …'; end)
  Downside is that this is more code in sub-classes and is more of a Objective-C (or C++, or Java, …) thing than a good Ruby paradigm.

Answer 1

Slipp, I read your question carefully. There is no way you can have 2 different methods called full_name defined on the same object at the same time. BUT, you could do something like this:

module MacroMethods
  private
  def full_name(full_name)
    # non-trivial, one-time-only set-up code exists here in actual usage
    # 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
  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