You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: toolbarImage.rb
    path of file: ./repos/Cookbook/ruby/gtk3
    
    the code of the file until where you have to start completion: #!/usr/bin/ruby

'''
ZetCode Ruby GTK tutorial

This example creates a simple toolbar.

Author: Jan Bodnar
Website: www.zetcode.com
Last modified: May 2014
'''

require 'gtk3'


class RubyApp < Gtk::Window

    def initialize
        super
        
        init_ui
    end
    
    def init_ui
    
        toolbar = Gtk::Toolbar.new
        toolbar.set_toolbar_style Gtk::Toolbar::Style::ICONS

        newtb = Gtk::ToolButton.new :stock_id => Gtk::Stock::NEW
        opentb = Gtk::ToolButton.new :stock_id => Gtk::Stock::OPEN
        savetb = Gtk::ToolButton.new :stock_id => Gtk::Stock::SAVE
        sep = Gtk::SeparatorToolItem.new
        quittb = Gtk::ToolButton.new :stock_id =
    
    def init_ui
    
        toolbar = Gtk::Toolbar.new
        toolbar.set_toolbar_style Gtk::Toolbar::Style::ICONS

        newtb = Gtk::ToolButton.new :stock_id => Gtk::Stock::NEW
        opentb = Gtk::ToolButton.new :stock_id => Gtk::Stock::OPEN
        savetb = Gtk::ToolButton.new :stock_id => Gtk::Stock::SAVE
        sep = Gtk::SeparatorToolItem.new
        quittb = Gtk::ToolButton.new :stock_id => Gtk::Stock::QUIT
       
        toolbar.insert newtb, 0
        toolbar.insert opentb, 1
        toolbar.insert savetb, 2
        toolbar.insert sep, 3
        toolbar.insert quittb, 4
        
        quittb.signal_connect "clicked" do
            Gtk.main_quit
        end

        vbox = Gtk::Box.new :vertical, 2
        vbox.pack_start toolbar, :expand => false, 
            :fill => false, :padding => 0

        add vbox
        
        set_title "Toolbar"
        signal_connect "destroy" do 
            Gtk.main_quit 
        end        

        set_default_size 300, 200
        set_window_position :center
        
        show_all        
    end