Question

I have a class whose new method has been made private because I want only my class method “constructors” to create new instances. However, I also now need to have some instance methods create new instances too.

For example, look at the following snippet. It is in method_a where I’m having trouble:

Class Foo

  class << self

    #a "constructor" method
    def from_x arg
      stuff_from_arg = arg.something #something meaningful from arg
      new(stuff_from_arg)
    end
  end

  def initialize stuff
    @stuff = stuff
  end

  private_class_method :new #forces use of Foo.from_x

  def method_a
    other_stuff = "blah"
    #These do not work
    return new(blah) #nope, instance cannot see class method
    return self.class.new(blah) #nope, new is private_class_method
    return Foo.new(blah) #same as previous line
    return initialize(blah) #See *, but still doesn't work as expected
  end
end

What I’m starting to think is that I may have designed this class in such a way that I need to make another class constructor method to create a new Foo, like this:

#in addition to previous code
Class Foo
  class << self
    def just_like_new stuff
      new(stuff)
    end
  end
end

This doesn’t feel very right or very DRY, but perhaps this is the bed I’ve made for myself. Is there anything I can do?

*This line has been a bit surprising. It returns blah. Outside of a class definition, there is also an initialize and it takes 0 arguments and returns nil Does anyone know what is happening here?

Answer 1

You can always use send to get around the access control:

def from_x arg
  stuff_from_arg = arg.something #something meaningful from arg
  self.class.send(:new, stuff_from_arg)
end