About

This is the repository for a Ruby metaprogramming workshop I designed and held at Redtail Technology in 2019. The workshop teaches metaprogramming techniques through test-driven construction of a simple data factory modeled after FactoryBot. Topics covered include:

• executing blocks in the context of another class using instance_eval
• dynamically setting attributes on objects with send
• dynamic arguments using splat * and double-splat **
• writing methods that accept blocks and how they relate to procs/lambdas
• acquiring an object's class with self.class
• using method_missing to hook into Ruby's method lookup chain
• using proxy classes to enable context-aware DSLs like traits

By the end of the workshop, developers will build a working data factory that supports traits and attribute overrides:

class Bicycle
  attr_accessor :style, :size, :color, :weight, :gears
end

Factory.define :bicycle, class: Bicycle do
  size :medium
  color :red

  trait :road do
    style :road
    gears 22
    weight 20
  end

  trait :fixed_gear do
    style :fixed_gear
    gears 1
    weight 17
  end

  trait :blue do
    color :blue
  end
end

it 'builds a large, blue road bike' do
  bicycle = Factory.run(:bicycle, :road, :blue, size: :large)
  assert_equal :large, bicycle.size
  assert_equal :blue, bicycle.color
  assert_equal :road, bicycle.style
  assert_equal 22, bicycle.gears
  assert_equal 20, bicycle.weight
end

Directory

The workshop contains 6 lessons. Each lesson has a corresponding branch. Run git checkout [branch name] to view the branch locally or use the links below to view on github.

Branch Name	GitHub Link
1-intro	Intro
2-blocks	Blocks
3-basic-dsl	Basic DSL
4-method-missing	Method Missing Refactor
5-traits-simple	Traits - Simple
5-traits-proxy	Traits - With Proxy
5-traits-multiple	Traits - Multiple
6-attribute-overrides	Attribute Overrides

Installation

Clone this repository

git clone https://github.com/davidtkramer/factory-workshop.git

Install dependencies

bundle install

If you get an error about an incorrect bundler version, run the command below and then try running bundle install again

gem update --system

If that still doesn't fix it, then install the latest version of bundler and then run bundle install again

gem install bundler

Checkout the first branch

git checkout 1-intro

Run the tests in watch mode

bundle exec guard