Ruby code explainers

class DigestMailer < ApplicationMailer
  default from: "notifications@example.com"
 
  def weekly_digest(user)

class OrdersController < ApplicationController
  rescue_from ActiveRecord::RecordNotUnique, with: :handle_duplicate_submission
 
  def create

class InventoryItem < ApplicationRecord
  belongs_to :warehouse
 
  validates :quantity, numericality: { greater_than_or_equal_to: 0 }

require "forwardable"
 
class ShoppingCart
  extend Forwardable

class PaymentMethod < ApplicationRecord
  belongs_to :account
 
  encrypts :card_number, deterministic: false

require "zlib"
require "stringio"
require "base64"
 

class SignupValidator
  EMAIL_REGEX = /\A[^@\s]+@[^@\s]+\.[^@\s]+\z/
  MIN_PASSWORD_LENGTH = 8
 

class QueryBuilder
  def initialize(table)
    @table = table
    @wheres = []

class DurationParser
  UNIT_SECONDS = {
    'w' => 604_800,
    'd' => 86_400,

class User < ApplicationRecord
  has_secure_password
 
  normalizes :email, with: ->(email) { email.strip.downcase }

class SemanticVersion
  include Comparable
 
  attr_reader :major, :minor, :patch, :prerelease

class Account < ApplicationRecord
  has_many :projects, dependent: :destroy_async
  has_many :memberships, dependent: :destroy_async
  has_many :invoices, dependent: :restrict_with_error

require "digest"
 
class UploadDeduplicator
  CHUNK_SIZE = 64 * 1024

require "csv"
 
class Api::V1::ProductImportsController < Api::V1::BaseController
  MAX_ROWS = 10_000

class WeightedSampler
  def initialize(weights)
    @entries = weights.to_a
    @total = @entries.sum { |_, w| w }

class HealthController < ApplicationController
  skip_before_action :authenticate_user!, raise: false
  skip_forgery_protection
 

class ContactImporter
  def initialize(rows)
    @rows = rows
  end

module Instrumentation
  module Timing
    def self.[](*method_names)
      Module.new do