Ruby code explainers

class PaymentGateway
  class MissingCredentialError < StandardError; end
 
  def initialize(env: Rails.env)

class WelcomeSequenceOrchestrator
  STEPS = [
    { mailer: :welcome_email,      delay: 0.hours },
    { mailer: :getting_started,    delay: 1.day },

class QueryProxy
  ALLOWED = %i[where limit offset order includes distinct].freeze
 
  def initialize(relation, operations = [])

class Debouncer
  def initialize(delay:)
    @delay = delay
    @mutex = Mutex.new

require "net/http"
require "json"
 
class UrlFetcher

class SyncContactsJob < ApplicationJob
  queue_as :external_api
 
  MAX_CONCURRENCY = 5

module DeepImmutable
  module_function
 
  def deep_freeze(obj)

class Admin::OrdersExportController < Admin::BaseController
  include ActionController::Live
 
  def show

class DatasetImportJob < ApplicationJob
  queue_as :default
 
  def perform(import)

class Booking < ApplicationRecord
  belongs_to :room
  belongs_to :guest
 

class DashboardMetrics
  CACHE_TTL = 15.minutes
 
  def initialize(account)

class LRUCache
  def initialize(capacity)
    raise ArgumentError, "capacity must be positive" unless capacity.positive?
 

class QueryParser
  def self.parse(query_string)
    new(query_string).parse
  end

class Article < ApplicationRecord
  belongs_to :author, class_name: "User"
  has_many :taggings, dependent: :destroy
  has_many :tags, through: :taggings

class Order
  class InvalidTransition < StandardError; end
 
  TRANSITIONS = {

class CreateOrderItems < ActiveRecord::Migration[7.1]
  def change
    create_table :order_items do |t|
      t.references :order, null: false, foreign_key: { on_delete: :cascade }

class Registration < ApplicationRecord
  belongs_to :event
 
  validates :email, presence: true, format: { with: URI::MailTo::EMAIL_REGEXP }

class ApacheLogParser
  LINE_PATTERN = /\A(?<ip>\S+)\s\S+\s\S+\s\[(?<time>[^\]]+)\]\s"(?<method>[A-Z]+)\s(?<path>\S+)\s(?<protocol>[^"]+)"\s(?<status>\d{3})\s(?<bytes>\d+|-)/
 
  TIME_FORMAT = "%d/%b/%Y:%H:%M:%S %z"