In the beginning, there was require...

Almost every Ruby program begins with the "require" method, but many of us don't pause to think about what it's doing until it fails us.

What happens when we call "require"? How does Ruby find what we're looking for? Is Bundler somehow involved? What about "require_relative" and "require_dependency"?

This talk will guide beginner and intermediate Rubyists through these foundational concepts that power our Ruby programs, from single-file script to a behemoth Rails 6 app.

Transcript

1. IN THE BEGINNING THERE WAS REQUIRE
2. CONFESSION https://pxhere.com/en/photo/458183
3. class ActiveStorage::Blob < ActiveRecord::Base require_dependency "active_storage/blob/analyzable" require_dependency "active_storage/blob/identifiable" require_dependency "active_storage/blob/representable" # ...
4. CARGO CULTING
5. 12 YEARS photo by John Nebbia
7. WHO AM I? Adam McCrea @adamlogic You Need A Budget (YNAB) Rails Autoscale
8. DEPENDENCIES standard library Rubygems within a project Photo by Iker Urteaga on Unsplash
9. PHP include 'banana.php';
10. NODEJS const fs = require("fs"); const banana = require("./banana.js");
11. ES6 import fs from "fs"; import banana from "./banana.js";
12. RUBY require require_relative require_dependency load autoload Bundler.require ✨ Rails ✨
15. REQUIRE A STANDARD LIBRARY > CSV # NameError (uninitialized constant CSV) > require 'csv' # true > CSV # CSV > require 'csv' # false
16. > Kernel.methods.sort # [ :attr_accessor, # :attr_reader, # :attr_writer, # ... # :puts, # :raise, # :require, # :require_relative, # ...
17. > $LOAD_PATH.inspect # [ "/Users/adam/.asdf/plugins/ruby/rubygems-plugin", # ... # "/Users/adam/.asdf/installs/ruby/2.6.4/lib/ruby/2.6.0", # ...
18. > $LOADED_FEATURES.inspect # [ ... # "/Users/adam/.../ruby/2.6.0/csv/writer.rb", # "/Users/adam/.../ruby/2.6.0/csv/version.rb", # "/Users/adam/.../ruby/2.6.0/csv.rb"]
19. REQUIRE A GEM > Minitest # NameError (uninitialized constant Minitest) > require 'minitest' # true > Minitest # Minitest
20. GEM ACTIVATION > $LOAD_PATH.grep(/minitest/) # [] > require 'minitest' # true > $LOAD_PATH.grep(/minitest/) # [".../ruby/2.6.4/lib/ruby/gems/2.6.0/gems/minitest-5.11.3/lib"]
21. KERNEL#REQUIRE FROM RUBYGEMS Check LOADED_FEATURES Check LOAD_PATH Check for a matching installed gem Add gem's lib* dir to LOAD_PATH Resume default require behavior
22. Gem::Specification.new do |spec| spec.require_path = "lib" ...
23. REQUIRE WITHIN A PROJECT ~/project ├── main.rb └── lib └── example.rb # main.rb require 'example' require 'lib/example'
24. REQUIRE WITHIN A PROJECT ~/project ├── main.rb └── lib └── example.rb # main.rb require '/Users/Adam/project/lib/example'
25. REQUIRE WITHIN A PROJECT ~/project ├── main.rb └── lib └── example.rb # main.rb require './lib/example' $ ruby project/main.rb
26. ADD TO LOAD PATH ~/project ├── main.rb └── lib └── example.rb # main.rb $LOAD_PATH.unshift File.join(File.dirname(__FILE__), 'lib') require 'example'
27. ALTER LOAD_PATH AT RUNTIME ~/project ├── main.rb └── lib └── example.rb $ ruby -I lib main.rb
28. ALTER LOAD_PATH AT RUNTIME ~/project ├── main.rb └── test ├── test_helper.rb └── example_test.rb # example_test.rb require 'test_helper' $ ruby -I test test/example_test.rb
30. REQUIRE RELATIVE ~/project ├── main.rb └── lib └── example.rb # main.rb require './lib/example' require_relative 'lib/example'
32. LOAD > load './lib/example.rb' # true > load './lib/example.rb' # true > load './lib/example.rb' # true
34. GEM VERSIONS > require 'minitest' # true $ gem list minitest # minitest (5.12.2, 5.11.3) > Minitest::VERSION # "5.12.2"
35. BUNDLER # Gemfile gem 'minitest', '~> 5.11.0' ❯ bundle install # Resolving dependencies... # Using minitest 5.11.3
36. # Gemfile.lock GEM specs: minitest (5.11.3)
37. > require 'minitest' # true > Minitest::VERSION # "5.12.2"
38. > require 'bundler' > Bundler.setup > $LOAD_PATH # [ "/Users/adam/.asdf/plugins/ruby/rubygems-plugin", # ".../ruby/2.6.4/lib/ruby/gems/2.6.0/gems/minitest-5.11.3/lib", # ... > require 'minitest' # true > Minitest::VERSION # "5.11.3"
39. > require 'bundler' > Bundler.require > Minitest::VERSION # "5.11.3"
40. # Gemfile gem 'minitest', '~> 5.11.0', require: false
42. KERNEL#AUTOLOAD # lib/example.rb class Example puts "Example has loaded" end # main.rb $LOAD_PATH.unshift File.join(File.dirname(__FILE__), 'lib') autoload :Example, 'example' Example # Example has loaded
43. # rack-2.0.6/lib/rack.rb autoload :Builder, "rack/builder" autoload :BodyProxy, "rack/body_proxy" # ... 40 more autoloads
45. > defined? User # nil > User.new # #<User:0x00007fd6547a88e8> > defined? User # "constant"
46. class UsersController < ApplicationController def new @user = User.new end end
47. AUTOLOAD_PATHS app/controllers app/models app/* app/*/concerns
48. $LOAD_PATH != autoload_paths # lib/example.rb class Example end # users_controller.rb require 'example'
51. # app/models/active_storage/blob.rb class ActiveStorage::Blob < ActiveRecord::Base require_dependency "active_storage/blob/analyzable" require_dependency "active_storage/blob/identifiable" require_dependency "active_storage/blob/representable" include Analyzable include Identifiable include Representable # ... end
53. TAKEAWAYS
54. STANDARD LIBRARIES require 'csv'
55. GEMS require 'minitest' # OR Bundler.setup require 'minitest' # OR Bundler.require
56. WITHIN A PROJECT (NON-RAILS) require_relative 'lib/example' # OR $LOAD_PATH.unshift File.join(File.dirname(__FILE__), 'lib') require 'example' # OR autoload :Example, 'example'
57. WITHIN A PROJECT (RAILS) embrace implicit autoloading expclicitly require files in lib
58. Photo by Laurie-Anne Robert on Unsplash
59. THANK YOU! Comments/Questions: @adamlogic (or come talk to me) ynab.com railsautoscale.com