Performance benchmark script for new implementation proposal of `Class#class_attribute`

class_attribute_benchmark.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  fail e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails'
  gem 'benchmark-ips'
end

require 'active_support'
require 'active_support/core_ext/object/blank'
require 'minitest/autorun'
require 'benchmark/ips'

class Parent
  class_attribute :parent_attr
end

class Mid < Parent
  class_attribute :mid_attr
end

class Child1 < Mid
end

class Child2 < Mid
end

class BugTest < Minitest::Test
  def test_class_attribute
    assert Parent.parent_attr.nil?
    assert Mid.parent_attr.nil?
    assert Child1.parent_attr.nil?
    assert Child2.parent_attr.nil?

    Parent.parent_attr = true
    assert Parent.parent_attr
    assert Mid.parent_attr
    assert Child1.parent_attr
    assert Child2.parent_attr

    Parent.parent_attr = false
    assert Parent.parent_attr == false
    assert Mid.parent_attr == false
    assert Child1.parent_attr == false
    assert Child2.parent_attr == false

    Mid.parent_attr = true
    assert Parent.parent_attr == false
    assert Mid.parent_attr
    assert Child1.parent_attr
    assert Child2.parent_attr

    Mid.mid_attr = []
    assert Mid.mid_attr == []
    assert Child1.mid_attr == []
    assert Child2.mid_attr == []

    Child1.mid_attr << 1
    assert Mid.mid_attr.include?(1)
    assert Child1.mid_attr.include?(1)
    assert Child2.mid_attr.include?(1)

    Child1.mid_attr += [2]
    Mid.mid_attr = []
    assert Mid.mid_attr == []
    assert Child1.mid_attr.include?(1)
    assert Child1.mid_attr.include?(2)
    assert Child2.mid_attr == []

    Child2.mid_attr << 5
    assert Mid.mid_attr.include?(5)
    assert !Child1.mid_attr.include?(5)
    assert Child2.mid_attr.include?(5)

    object = Class.new { class_attribute :setting, instance_accessor: true }.new

    Benchmark.ips do |x|
      x.report('reading low class attribute') { Child1.parent_attr }
      x.report('reading high class attribute') { Parent.parent_attr }
      x.report('writing low class attribute') { Child1.parent_attr = rand }
      x.report('writing high class attribute') { Parent.parent_attr = rand }
      Child1.parent_attr = 1
      Parent.parent_attr = 1
      x.report('r+w low class attribute') { Child1.parent_attr += 1 }
      x.report('r+w high class attribute') { Parent.parent_attr += 1 }
      x.report('reading instance') { object.setting }
      x.report('writing instance') { object.setting = rand }
    end
  end

  def inspect_all
    puts "P.p: #{Parent.parent_attr}"
    puts "M.p: #{Mid.parent_attr}"
    puts "C1.p: #{Child1.parent_attr}"
    puts "C2.p: #{Child2.parent_attr}"
    puts "M.m: #{Mid.mid_attr}"
    puts "C1.m: #{Child1.mid_attr}"
    puts "C2.m: #{Child2.mid_attr}"
  end
end