红宝石：在没有父类的情况下调用super

Question

I have a class which overrides self.new and calls super in it, but the class doesn't derive from antoher class. So what exactly does the call?

class Test
  attr_reader :blatt

  def self.new(blatt, quellformat, &block)
    begin
      # why can't I call initialize(blatt,quellformat) here? 
      # when I try this, it only prints "wrong # of arguments(2 for 1)"

      a = super(blatt, quellformat) # but this works...

      # some code
      a
    end
  end

  def initialize(blatt, quellformat)
    @name = blatt.blattname
    @datei = blatt.datei
    @blatt = blatt
    @qu = quellformat
  end
end

Answer 1

Classes inherit from Object by default. Hence, your super call will call Object.new .

Answer 2

why can't I call initialize(blatt,quellformat) here?

Because Test::new is a class method and Test#initialize is an instance method. You need an instance of your class to call initialize .

By defining self.new , you're replacing Class#new . According to the documentation:

Calls allocate to create a new object of class ’s class, then invokes that object's initialize method, passing it args .

A Ruby implementation would look like this:

def self.new(*args)
  obj = allocate
  obj.send(:initialize, *args)
  obj
end

Calling super simply invokes the default implementation, ie Class#new , which does the same. Here's the C code:

VALUE
rb_class_new_instance(int argc, const VALUE *argv, VALUE klass)
{
    VALUE obj;

    obj = rb_obj_alloc(klass);
    rb_obj_call_init(obj, argc, argv);

    return obj;
}