Dynamic class loading: Is there a "method_missing" for classes in Ruby?

Question

On a Rails application I'm working on, I have a model "Type" that relates to the single-table-inheritance model "Node": any possible subclass of Node is defined as a Type in the types table.

Right now this is made possible loading all classes in an initializer, but I'd like to load the subclasses only when they are required.

The best solution I can think of would be having a fallback on an uninitialized constant that would check if that constant can represent a class in the application, something similar to what method_missing does.

I'd like some advice on how and where to define this logic, or if there's a better solution altogether.

Answer 1

I don't know if this is new but as I thought it was worth adding. It is possible to use method missing as a class method

class Example
  def method_missing(method_name, *arguments, &block)
    puts 'needs this instance method'
  end

  def self.method_missing(method_name, *arguments, &block)
    puts 'needs this class method'
  end
end

Answer 2

there's const_missing method: it works like method_missing but it's about constants

http://ruby-doc.org/core/classes/Module.html#M000489

Answer 3

There's Module#const_missing:

http://apidock.com/ruby/Module/const_missing

I assume you can (ab)use that for your needs.

Answer 4

Maybe you can rescue an undefined constant error and load/create your classes.