Calling a method of a Ruby Singleton without the reference of 'instance'

Question

I would like to call a method of a Singleton Object without the reference to its instance

SingletonKlass.my_method

instead of

S         


        

Answer 1

The problem with your method_missing solution is that it will only redirect calls to instance if there does not exist a method of that name on SingletonKlass, which will cause problems if people want to access, for example, instance.__id__ through this interface you provide. There is not much of a problem with accessing SingletonKlass.instance the normal way, but if you really want to make a shortcut, the safest would be a constant:

KlassInstance = SingletonKlass.instance

If you want to define the constant dynamically, use Module#const_set:

const_set :KlassInstance, SingletonKlass.instance

You can extend upon this, too. For example, you can create a method that will create constants like this for you:

def singleton_constant(singleton_class)
  const_set singleton_class.name, singleton_class.instance
end

Of course, because Module#const_set is a method of a module, this specific technique can only be performed in the context of a module or class. Another possibility is by a mixin module with an overloaded hook method:

module SingletonInstance
  def included(base_class)
    const_set base_class.name, base_class.instance
    super
  end
end