Metaprogramming Ruby 2

Hook Methods

Where you get one of Bill’s thorough lessons in advanced coding.

The object model is an eventful place. Lots of things happen there as your code runs: classes are inherited, modules are mixed into classes, and methods are defined, undefined, and removed. Imagine if you could “catch” these events like you catch GUI mouse-click events. You’d be able to execute code whenever a class is inherited or whenever a class gains a new method.

Well, it turns out you can do all these things. This program prints a notification on the screen when a class inherits from String:

ctwc/hooks.rb

class String
  def self.inherited(subclass)
    puts "#{self} was inherited by #{subclass}"
  end
end

class MyString < String; ...