Ruby Meta-Programming for beginners

Presentation used for the OpenTechSchool Hackership (http://www.hackership.org/) introduction to Meta-Programming in Ruby mini-workshop.

Transcript

1. Meta Programming in Ruby
2. whoami Amir Friedman • Developer at DaWanda (we’re hiring!) • Vegetarian • amirf@null.co.il • @NewArtRiot • http://github.com/psychocandy
3. What is “Meta Programming”?
4. “Code that treats code as data”
5. “Anything that would blow the mind of a Java developer”
6. “Code that writes code”
7. “There is no such thing as MP, there’s just programming”
8. What are we going to learn • Clear uncertainty regarding MP • Show different layers of MP • Make you feel secure about MP • Show examples from the real-world
9. Some Basic Concepts • Method manipulation • Class definition • Module definition • Mixin
10. The Ruby Ancestors Chain Let’s open pry (irb)! > self.class.ancestors => [Object, PP::ObjectMixin, Kernel, BasicObject] > class Greeting ; end > Greeting.ancestors => ? > module Hello ; end ...
11. Ancestors Chain class Greeting if rand(2) == 0 include X else include Y end end We redirect messages during runtime :)
12. 1st Layer • “Monkey Patching” (class, kernel method) • attr_… (attr_accessor, _reader, etc.) • alias :new_name :old_name
13. 2nd Layer Idoms: • method_missing(sym, args) • respond_to? • “around_alias” (keep reference to the original)
14. 3rd Layer • class_eval • instance_eval • define_method • dynamic include/extend
15. Let’s take a look at Rails and RSpec > require ‘rails’