These are the slides and example files used for the MDC 2011 presentation I did on metaprogramming.

Most of the material of interest is in the .rb files:

Open classes:

• Adding new methods to an existing class: see ord.rb (the String class)
• Overriding existing methods: see apples_and_oranges.rb (we override ==)

Hook methods:

• inherited and at_exit in testy_testy.rb and some_test.rb
• included example in apples_and_oranges.rb
• a bit about the included idiom as used in rails acts_as style plugins, in acts_as_something.rb

Method missing:

• friendlier errors and delegation: person_permissions.rb
• flexible apis: see the Array class in ord.rb
• more on flexible apis: look up how ActiveRecord handles methods like find_by_name_and_email_and_age, etc.

DSLs

• an rspec-like thing: specky.rb (based off a Gary Bernhardt screencast)

Ruby macros:

• something that works like attr_accessor, but accepts a block with an initial value for the attribute: object_accessor.rb

That's about it. Take a look through the slides, try to run and understand the example files, and play around with classes and objects in irb.

Also in the repo is Paul Cantrell's closures-in-ruby.rb, which I never got around to talking about in the presentation, but which is really interesting, and which you'll probably enjoy if you like this sort of thing.