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
   

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2. whoami
   Amir Friedman
   ● Developer at DaWanda (we’re hiring!)
   ● Vegetarian
   ● amirf@null.co.il
   ● @NewArtRiot
   ● http://github.com/psychocandy
   

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3. What is “Meta Programming”?
   

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4. “Code that treats code as data”
   

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5. “Anything that
   would blow the
   mind of a Java
   developer”
   

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6. “Code that writes code”
   

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7. “There is no such thing as MP,
   there’s just programming”
   

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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
   

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9. Some Basic Concepts
   ● Method manipulation
   ● Class definition
   ● Module definition
   ● Mixin
   

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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
    ...
    

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11. Ancestors Chain
    class Greeting
    if rand(2) == 0
    include X
    else
    include Y
    end
    end
    We redirect messages during runtime :)
    

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12. 1st Layer
    ● “Monkey Patching” (class, kernel method)
    ● attr_… (attr_accessor, _reader, etc.)
    ● alias :new_name :old_name
    

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13. 2nd Layer
    Idoms:
    ● method_missing(sym, args)
    ● respond_to?
    ● “around_alias” (keep reference to the original)
    

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14. 3rd Layer
    ● class_eval
    ● instance_eval
    ● define_method
    ● dynamic include/extend
    

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15. Let’s take a look at Rails
    and RSpec
    > require ‘rails’
    

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