age = 49
name = "David"
user = { name:, age: }

# When exceeding 100 lines, extract secondary concerns:
class UserProfilePresenter  # Presentation logic
class UserProfileValidator  # Validation logic
class UserProfileNotifier   # Notification logic

# Good - 5 lines or fewer
def process_order
  validate_order
  calculate_totals
  apply_discounts
  finalize_payment
end

# Avoid - extract when too long
def process_order
  return unless items.any?
  return unless valid_address?
  self.subtotal = items.sum(&:price)
  self.tax = subtotal * tax_rate
  self.total = subtotal + tax
  charge_customer
  send_confirmation
end

# Parameter object when data is related
def create_post(post_params)
  Post.create(user: post_params.user, title: post_params.title, content: post_params.content)
end

# Good - single object via facade
class DashboardController < ApplicationController
  def show
    @dashboard = DashboardFacade.new(current_user)
  end
end

# Avoid - multiple instance variables
class DashboardController < ApplicationController
  def show
    @user = current_user
    @posts = @user.posts.recent
    @notifications = @user.notifications.unread
  end
end

class Configuration
  @instance_mutex = Mutex.new

  def self.instance
    return @instance if @instance
    @instance_mutex.synchronize { @instance ||= new }
  end
end

def activate_user
  return if user.active?
  user.update(active: true)
  send_activation_email unless email_sent?
end