An abstract class to represent null objects

null_object.rb

# frozen_string_literal: true

class NullObject
  class << self
    SOFT_DEFAULTS = {
      array: [],
      hash: {},
      null: nil
      null_object: NullObject
    }.freeze
    
    def attr_with_soft_default(method_name, soft_default)
      define_method method_name do
        soft_default_value(soft_default)
      end
    end
    
    private
    
    def soft_default_value(soft_default)
      if soft_default <= NullObject
        soft_default.new
      else
        SOFT_DEFAULTS.fetch(soft_default)
      end
    end
  end
end


## example subclass

class NullProduct < NullObject
  attr_with_soft_default :variants, :array
  attr_with_soft_default :available_on, :null
  attr_with_soft_default :fragrance, NullFragrance
end