Ruby on Rails - Abstract class and STI. Make any class an Abstract class at any level of STI. Raise error when abstract class instantiated.

abstractable.rb

module Abstractable
  extend ActiveSupport::Concern

  included do
    class << self
      attr_accessor :isabstract
    end
    @isabstract = true
  end

  def initialize(*args)
    # Raise custom error
    raise CustomError::AbstractClass.new(self.class) if self.class.isabstract
    super
  end

  module ClassMethods
    def inherited(subklass)
      subklass.instance_variable_set('@isabstract', instance_variable_get('@isabstract'))
      super
    end
  end
end

custom_error.rb

module CustomError
  class Error < StandardError; end

  class AbstractClass < CustomError::Error
    attr_reader :klass_object, :message
    attr_writer :default_message

    def initialize(klass_object = nil, message = nil)
      @message = message
      @klass_object = klass_object
      @default_message = "Can not instantiate abstract class. Type has to be specified."
      
      if klass_object.present? && Object.const_defined?(klass_object.to_s)
        descendants_list = klass_object.try(:descendants).try(:reject, &:isabstract).try(:map, &:name).try(:map, &:demodulize).try(:join, ', ')
        @default_message += " #{klass_object.to_s} can be one of type: #{descendants_list}."
      end
    end

    def to_s
      @message || @default_message
    end
  end
end

model_sample.rb

module TopLevelModule
  class SomeBaseClass < ApplicationRecord
    # By default it will make this class and its child classes an Abstract class
    # after including the Abstractable module
    include Abstractable
  end

  module SomeNameSpace1
    class SomeChildClass1 < TopLevelModule::SomeBaseClass
      # Makes the child class non-abstract
      @isabstract = false
    end
    
    class SomeChildClass2 < TopLevelModule::SomeBaseClass
      @isabstract = false
    end

    class SomeChildClass3 < TopLevelModule::SomeBaseClass
      @isabstract = false
    end
  end

  class AnotherChildClass < TopLevelModule::SomeBaseClass
    # An abstract class.
  end

  module SomeNameSpace2
    class SomeOtherChild1 < TopLevelModule::AnotherChildClass
      @isabstract = false
    end
    class SomeOtherChild2 < TopLevelModule::AnotherChildClass
      @isabstract = false
    end
  end
end