ruby

class Money
  include Comparable

  attr_reader :amount, :currency

  def initialize(amount, currency = 'USD')

# app/mailers/user_mailer.rb
class UserMailer < ApplicationMailer
  default from: 'noreply@example.com'

  def welcome_email(user)
    @user = user

# BAD: N+1 query problem
@users = User.all
@users.each do |user|
  puts user.posts.count  # Fires query for each user!
end

# Installation
# rails active_storage:install
# rails db:migrate

# config/storage.yml
local:

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  def subscribed
    # Subscribe to a specific room
    room = Room.find(params[:room_id])

# app/validators/order_validator.rb
class OrderValidator < ActiveModel::Validator
  def validate(record)
    validate_order_total(record)
    validate_items_availability(record)
    validate_shipping_address(record)

class UserRegistrationService
  class Result
    attr_reader :user, :errors

    def initialize(success:, user: nil, errors: [])
      @success = success

# Define refinements in a module
module StringExtensions
  refine String do
    def titleize
      split.map(&:capitalize).join(' ')
    end

# Basic matching
email = "user@example.com"
email =~ /@/  # => 4 (position of match)
email.match?(/@/)  # => true

# Capture groups

# Create table migration
class CreateUsers < ActiveRecord::Migration[7.0]
  def change
    create_table :users do |t|
      t.string :email, null: false, index: { unique: true }
      t.string :name, null: false

class UserRegistrationForm
  include ActiveModel::Model
  include ActiveModel::Attributes

  attribute :email, :string
  attribute :name, :string

# Simple mixin
module Loggable
  def log(message)
    puts "[#{Time.now}] #{self.class.name}: #{message}"
  end
end