How can I initialize a module's instance variables in Ruby?

I have some modules where I would like to use instance variables in. I'm currently initializing them like this:

module MyModule
  def self.method_a(param)
    @var ||= 0
    # other logic goes here
  end
end

I also could call a init method to initialize them:

def init
  @var = 0
end

but this would mean I have to remember to always call it.

Is there a better way of doing this?