gistfile1.rb

class User
  attr_accessor :products

  def initialize
    @products = ProductsArray.new
  end

end

class ProductsArray < Array

  def <<(obj)
    super(obj)
    puts "you've pushed an object onto the array"
  end

end

usr = User.new
usr.products << 'test'

p usr

You should probably use:

  def <<(obj)
    super(obj).tap do
      puts "you've pushed an object onto the array"
    end
  end

so products << 1 << 2 still works, etc.

Aha! I wouldn't of known that, thanks =)

Link to docs: http://ruby-doc.org/core-1.9.3/Object.html#method-i-tap