Presentation given at RubyConf 2019. This is the source for my slides, used with Deckset (paid Mac app).

In the beginning, there was require.md

build-lists: true

In the beginning
there was require

---

confession

^ Story that led to this talk Custom processing video uploads Extend ActiveStorage 👇 Came across these lines

[.footer: https://pxhere.com/en/photo/458183]

---

class ActiveStorage::Blob < ActiveRecord::Base
  require_dependency "active_storage/blob/analyzable"
  require_dependency "active_storage/blob/identifiable"
  require_dependency "active_storage/blob/representable"

  # ...

^ Ruby? Rails? Shoved aside to complete task (lines were inconsequential) Rails engine Where it goes, how to organize and require Unfamiliar 👇 Find other engine examples, use them without understanding

---


Cargo culting

^ More often than I'd like to admit Got it working without understanding the glue The knowledge gap was uncomfortable 👇 Writing Ruby professionally for 12 years

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12 years

[.footer: photo by John Nebbia]

^ I didn't know how to require code 👇 Wrote the proposal for this talk

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^ All about requiring code in ruby We all do everyday My goal is to fill that knowledge gap 👇 Introduce myself

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Who am I?

• Adam McCrea
• @adamlogic
• You Need A Budget (YNAB)
• Rails Autoscale

^ Ruby 12 years, software for 18 years 👇 Requiring code... dependencies

---

dependencies

• standard library
• Rubygems
• within a project

[.footer: Photo by Iker Urteaga on Unsplash]

^ Three flavors Csv, open-url, logger Activerecord, rspec, minitest 👇 Every lang has a way

---

PHP

include 'banana.php';

---

NodeJS

const fs = require("fs");
const banana = require("./banana.js");

---

ES6

import fs from "fs";
import banana from "./banana.js";

---

Ruby

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require
require_relative
require_dependency
load
autoload
Bundler.require
✨ Rails ✨

^ Simple topic, not so simple Blindsided by how little I knew 👇 As I learned, made a mental model

---

^ Left, right, top, bottom 👇 Let's talk about require

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^ Require is the foundation 👇 To understand, let's see it in action

---

Require a standard library

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> CSV
# NameError (uninitialized constant CSV)

> require 'csv'
# true

> CSV
# CSV

> require 'csv'
# false

^ Requiring stdlib is the simplest example 👇 What is require?

---

> Kernel.methods.sort
# [ :attr_accessor,
#   :attr_reader,
#   :attr_writer,
#   ...
#   :puts,
#   :raise,
#   :require,
#   :require_relative,
#   ...

^ Just a method Can be overridden (see later) 👇 What happens when we pass "csv"?

---

> $LOAD_PATH.inspect
# [ "/Users/adam/.asdf/plugins/ruby/rubygems-plugin",
#   ...
#   "/Users/adam/.asdf/installs/ruby/2.6.4/lib/ruby/2.6.0",
#   ...

^ Load path set by Ruby We can add to it (later) 👇 Another global var...

---

> $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"]

^ Require return true/false csv.rb requires its own dependencies 👇 Requiring a gem is similar

---

Require a gem

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> Minitest
# NameError (uninitialized constant Minitest)

> require 'minitest'
# true

> Minitest
# Minitest

^ Must have gem installed 👇 Looks the same, subtle diff

---

Gem activation

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> $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"]

^ Rubygems overrides Kernel#require 👇 What does it do?

---

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

^ When you require something you're using the override But don't override it yourself 👇 Not necessarily lib dir

---

Gem::Specification.new do |spec|
  spec.require_path = "lib"
  ...

^ 👇 3rd thing we might want to require is within project

---

Require within a project

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~/project
├── main.rb
└── lib
    └── example.rb

# main.rb
require 'example'
require 'lib/example'

^ Goal: require example from main What happens? 👇 Alternatives?

---

Require within a project

~/project
├── main.rb
└── lib
    └── example.rb

# main.rb
require '/Users/Adam/project/lib/example'

^ Absolute file system path Starts with / Brittle, not portable

---

Require within a project

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~/project
├── main.rb
└── lib
    └── example.rb

# main.rb
require './lib/example'

$ ruby project/main.rb

^ Relative file system path Starts with ./ Better, but with a gotcha 👇 How to reliably require example?

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add to load path

~/project
├── main.rb
└── lib
    └── example.rb

# main.rb
$LOAD_PATH.unshift File.join(File.dirname(__FILE__), 'lib')
require 'example'

^ Works in an working directory Good for common root dir 👇 Another way to alter load_path at runtime

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alter load_path at runtime

~/project
├── main.rb
└── lib
    └── example.rb

$ ruby -I lib main.rb

^ Same behavior we just saw 👇 Very useful for running tests

---

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

^ 👇 What if we don't want to mess with load path?

---

^ 👇 Revisit relative path example

---

require relative

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~/project
├── main.rb
└── lib
    └── example.rb

# main.rb
require './lib/example'
require_relative 'lib/example'

^ Execute from anywhere Useful Sometimes load path is easier 👇 Quickly... Load

---

---

load

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> load './lib/example.rb'
# true

> load './lib/example.rb'
# true

> load './lib/example.rb'
# true

^ Note the file extension Re-evaluates target file Not useful for most apps 👇 Bundler

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^ 👇 To illustrate, revisit our minitest example

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gem versions

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> require 'minitest'
# true

$ gem list minitest
# minitest (5.12.2, 5.11.3)

> Minitest::VERSION
# "5.12.2"

^ How do we know which version gets used? How do we ensure others use the same version? 👇 Bundler...

---

Bundler

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# Gemfile
gem 'minitest', '~> 5.11.0'

❯ bundle install
# Resolving dependencies...
# Using minitest 5.11.3

^ Bundle install installs and locks 👇 When locking, creates Gemfile.lock

---

# Gemfile.lock
GEM
  specs:
    minitest (5.11.3)

^ Collaborators or prod environments will install the same version 👇 Now that we've run bundle install, let's try to require it again

---

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> require 'minitest'
# true

> Minitest::VERSION
# "5.12.2"

^ We've required it, which version did we get? Why didn't we get the locked version? Gem activation always uses latest installed version 👇 We need bundlers help to require

---

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> 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"

---

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> require 'bundler'
> Bundler.require

> Minitest::VERSION
# "5.11.3"

^ Can also require specific groups 👇 Can opt out in Gemfile

---

# Gemfile
gem 'minitest', '~> 5.11.0', require: false

^ No effect unless Bundler.require Must explicitly require 👇 That's Bundler

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^ Skipping require_dependency for now Entering lazy territory with autoload 👇 Let's see what that means

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Kernel#autoload

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# 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

^ Autoload calls require (LOAD_PATH) Reduces initial load 👇 Handy for libraries (like rack)

---

# rack-2.0.6/lib/rack.rb
autoload :Builder, "rack/builder"
autoload :BodyProxy, "rack/body_proxy"
# ... 40 more autoloads

^ Gem activation puts lib in load path 👇 This autoloading built into Ruby Rails autoloading different beast

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^ Implicit quadrants, both Rails No explicit requires for app code 👇 What does it look like?

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> defined? User
# nil

> User.new
# #<User:0x00007fd6547a88e8>

> defined? User
# "constant"

^ 👇 Let's us write code like this

---

class UsersController < ApplicationController
  def new
    @user = User.new
  end
end

^ No require for ApplicationController or User Where are they required from?

---

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autoload_paths

app/controllers
app/models
app/*
app/*/concerns

^ Missing constant (User) Convention: user.rb Paths within app AND gems 👇 LOAD_PATH != autoload_paths

---

$LOAD_PATH != autoload_paths

# lib/example.rb
class Example
end

# users_controller.rb
require 'example'

^ Lib not autoloaded Rails does add it to LOAD_PATH Require from lib, not app What if we added lib to autoload_paths? Come back to it. 👇 Autoload in dev, prod is different

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^ Dev optimized for fast boot, reloading Prod optimized for fast requests Eager require all files in autoload_paths Eager require lib can be dangerous 👇 Sometimes Rails needs eager loading ...even in dev

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^ Back where my journey began Part of Rails, not Ruby Explicit, eager, for Rails 👇 Why?... back to ActiveStoarge

---

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# 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

^ Rails would autoload these, so why eager load them? What if our app defined Analyzable? Why not require? 👇 Irony, not needed in Rails 6

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^ What led me down this path... Now irrelevant 👇 Takeaways

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Takeaways

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standard libraries

require 'csv'

^ Even in Rails

---

gems

require 'minitest'

# OR

Bundler.setup
require 'minitest'

# OR

Bundler.require

^ Done for you in Rails

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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'

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within a project (Rails)

embrace implicit autoloading

expclicitly require files in lib

^ App directories autoload, don’t require them Name your files and classes appropriately 👇 I hope this talk has filled knowledge gap

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[.footer: Photo by Laurie-Anne Robert on Unsplash]

^ Next time you encounter a gap, dive in! No shame 👇 Questions

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Thank you!

Comments/Questions: @adamlogic (or come talk to me)

ynab.com railsautoscale.com

^ Shirts, stickers Thanks so much