bench.rb

# frozen_string_literal: true

require 'bundler/inline'

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", path: "/Users/byroot/src/github.com/Shopify/rails"
  gem "benchmark-ips"
end

require 'rails'
require 'action_view'
require 'benchmark/ips'

class BenchView < ActionView::Base
  def compiled_method_container
    self.class
  end

  def self.compiled_method_container
    self
  end
end

view = BenchView.new(
  ActionView::LookupContext,
  {},
  nil,
)
locals = { message: "Hello World!"}
erb_template = <<~ERB
  <ul>
    <% 10.times do %>
      <li><%= message %>"</li>
    <% end %>
  </ul>
ERB
template = ActionView::Template.new(
  erb_template,
  "hello template",
  ActionView::Template::Handlers::ERB.new,
  virtual_path: "hello",
  locals: locals.keys,
)
puts template.render(
  view,
  locals,
)

Benchmark.ips do |x|
  x.report("ActionView::OutputBuffer") { template.render(view, locals, ActionView::OldOutputBuffer.new) }
  x.report("optimized buffer") { template.render(view, locals, ActionView::FastOutputBuffer.new) }
  x.compare!(order: :baseline)
end

results.txt

Warming up --------------------------------------
ActionView::OutputBuffer
                        14.691k i/100ms
    optimized buffer    22.712k i/100ms
Calculating -------------------------------------
ActionView::OutputBuffer
                        147.644k (± 1.4%) i/s -    749.241k in   5.075604s
    optimized buffer    228.001k (± 1.7%) i/s -      1.158M in   5.081631s

Comparison:
ActionView::OutputBuffer:   147644.2 i/s
    optimized buffer:   228001.4 i/s - 1.54x  (± 0.00) faster