why_lambda.rb

module ActiveRecord
  class Base
    def self.scope(name, callable)
      define_singleton_method name do
        options = callable.respond_to?(:call) ? callable.call : callable
        puts "Fetching records with options #{options.inspect}"
      end
    end
  end
end

class MyModel < ActiveRecord::Base
  scope :active1, { "published_at.lt" => Time.now }
  scope :active2, -> { puts 2 ; { "published_at.lt" => Time.now } }
end

MyModel.active1
sleep 1
MyModel.active1
sleep 1
MyModel.active1
sleep 1
MyModel.active1
sleep 1

MyModel.active2
sleep 1
MyModel.active2
sleep 1
MyModel.active2
sleep 1
MyModel.active2