Ruby Development

Apply these patterns when working with Ruby code.

Naming Conventions

Element	Convention	Example
Classes, Modules	PascalCase	UserService
Methods, variables	snake_case	find_user_by_id
Constants	SCREAMING_SNAKE	MAX_RETRIES
Predicates	snake_case?	active?
Dangerous methods	snake_case!	save!
Files	snake_case	user_service.rb

Project Structure

lib/
├── my_app.rb
└── my_app/
    ├── version.rb
    └── services/
spec/
├── spec_helper.rb
└── services/
Gemfile

Idioms

Blocks and Lambdas

users.map { |u| u.name }
users.map(&:name)  # Symbol to proc

double = ->(n) { n * 2 }
double.call(5)

Enumerable

users.select(&:active?)
users.reject(&:banned?)
users.find { |u| u.id == 5 }
users.group_by(&:country)
orders.sum(&:total)

users.select(&:active?).sort_by(&:created_at).first(10).map(&:email)

Safe Navigation

user&.profile&.avatar_url
name = user.name || "Anonymous"

def expensive_calculation
  @expensive_calculation ||= perform_calculation
end

Pattern Matching (Ruby 3+)

case response
in { status: 200, body: }
  process(body)
in { status: 404 }
  handle_not_found
end

Classes

class User
  attr_reader :id, :email
  attr_accessor :name

  def initialize(id:, email:, name: nil)
    @id = id
    @email = email
    @name = name
  end

  def active?
    @status == :active
  end

  private

  def save!
    # Persist changes
  end
end

Modules for Composition

module Timestampable
  def touch
    @updated_at = Time.current
  end
end

class User
  include Timestampable
end

Service Objects

class CreateUser
  def initialize(user_repository:, email_service:)
    @user_repository = user_repository
    @email_service = email_service
  end

  def call(email:, name:)
    user = @user_repository.create(email: email, name: name)
    @email_service.send_welcome(user)
    user
  end
end

Error Handling

module MyApp
  class Error < StandardError; end
  class NotFoundError < Error; end
  class ValidationError < Error
    attr_reader :errors
    def initialize(errors)
      @errors = errors
      super("Validation failed: #{errors.join(', ')}")
    end
  end
end

raise MyApp::NotFoundError, "User not found"

Result Objects

class Result
  attr_reader :value, :error

  def self.success(value) = new(value: value)
  def self.failure(error) = new(error: error)

  def success? = @error.nil?
  def failure? = !success?

  def then
    return self if failure?
    yield(value)
  end
end

Testing with RSpec

RSpec.describe UserService do
  subject(:service) { described_class.new(repository: repository) }
  let(:repository) { instance_double(UserRepository) }
  let(:user) { build(:user, id: 1, name: "John") }

  describe "#find_by_id" do
    context "when user exists" do
      before { allow(repository).to receive(:find).with(1).and_return(user) }

      it "returns the user" do
        expect(service.find_by_id(1)).to eq(user)
      end
    end
  end
end

Matchers

expect(result).to eq(expected)
expect(user).to be_nil
expect(list).to include(item)
expect { user.activate! }.to change(user, :status).to(:active)
expect { risky_op }.to raise_error(MyError)

Doubles

repository = instance_double(UserRepository)
allow(repository).to receive(:find).with(1).and_return(user)

mailer = instance_spy(UserMailer)
service.call
expect(mailer).to have_received(:send_welcome).with(user)

Requirements

1. Use composition over inheritance
2. Use keyword arguments for methods with 2+ parameters
3. Return early with guard clauses
4. Add # frozen_string_literal: true to every file
5. Use symbols for hash keys
6. Use Enumerable methods over manual iteration
7. Name predicate methods with ?
8. Raise exceptions only for exceptional cases; use Result objects for expected failures