Question

I still can’t figure out how to make a subclass constructor follow its parent…

example:

require 'mechanize'

class Scraper
    attr_accessor :agent

    def initialize 
    # I dont know if using instance variable is the right thing to do
    @agent = Mechanize.new 
    end
end

class ScraperA < Scraper
end

I want to make ScraperA follow its parent constructor behaviour,

that is
instantiate a Mechanize object without me retyping Mechanize.new in
ScraperA initialize() method. Is this possible ?

Just want to follow DRY principle but ruby makes it hard for me ???

Hope not, maybe it’s just my ignorance.
Looking forward for simple solution,Tnx.

Edit:

it turns out that I had empty initialize() method in ScraperA, which override the default
initialize().
So yeah the example is working, because no empty initialize method there.
Sorry for my stupidity.
Tnx.

Answer 1

Umm… eh? Yes it does… Check this out:

class A
  def initialize
    @a = "foo"
  end
end

class B < A
  def to_s
    @a
  end
end

puts B.new
# "foo" is printed

This works because initialize is inherited, just like any other method. If you override it by having a new sub-initialize, it stops working. Then you can explicitly use super to call the parent’s initialize.