bogdan_change_attributes.rb

require 'benchmark/ips'
require 'active_model'

# run this
# bundle exec ruby benchmark.rb && second_run=y bundle exec ruby benchmark.rb

class Person
  include ActiveModel::Dirty

  define_attribute_methods :name, :age

  def initialize(name)
    @name = name
  end

  def name=(val)
    name_will_change! unless val == @name
    @name = val
  end
end

n = 2000000

if ENV['second_run']
  module ActiveModel::Dirty
    def attribute_changed?(attr, from: :none, to: :none)
      result = changes_include?(attr)
      result &&= from == __send__(attr) unless from == :none
      result &&= to == changed_attributes[attr] unless to == :none
      result
    end
  end
end

Benchmark.ips do |x|
  x.hold! 'filename'

  proc = Proc.new {
    person = Person.new('tom')
    person.name = 'bob'

    n.times {
      person.attribute_changed?(:name)
      person.attribute_changed?(:age)
    }
  }

  x.report("unchanged", &proc)
  x.report("with nil", &proc)
  x.compare!
end