Jbuilder is faster than Ralb.

benchmark.rb

require 'benchmark/ips'
require 'active_support/core_ext'
require 'jbuilder'
require 'rabl'
require 'oj'

Benchmark.ips do |benchmark|
  struct = Struct.new(:name, :birthyear, :bio, :url)
  @author = struct.new("Rolf", 1920, "Software developer", "http://example.com/")
  @authors = Array.new(10, @author)

  # for jbuilder
  @author.instance_eval { undef map }

  # for rabl
  @scope = Object.new
  @scope.instance_variable_set :@author, @author
  @template_for_single_object = %{
    object @author => :author
    attribute :name, :birthyear, :bio, :url
  }

  @scope.instance_variable_set :@authors, @authors
  @template_for_collection = %{
    collection @authors => :authors
    attributes :name, :birthyear, :bio, :url
  }

  benchmark.report "Jbuilder(single obj)" do
    Jbuilder.encode do |json|
      json.author @author, :name, :birthyear, :bio, :url
    end
  end

  benchmark.report "Rabl(single obj)" do
    Rabl::Engine.new(@template_for_single_object).render(@scope, {})
  end

  benchmark.report "Jbuilder(collection)" do
    Jbuilder.encode do |json|
      json.authors @authors do |author|
        json.author author, :name, :birthyear, :bio, :url
      end
    end
  end

  benchmark.report "Rabl(collection)" do
    Rabl::Engine.new(@template_for_collection).render(@scope, {})
  end
end

Gemfile

source 'https://rubygems.org'

gem 'benchmark-ips'
gem 'activesupport'
gem 'jbuilder'
gem 'rabl'
gem 'oj'

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    activesupport (4.0.2)
      i18n (~> 0.6, >= 0.6.4)
      minitest (~> 4.2)
      multi_json (~> 1.3)
      thread_safe (~> 0.1)
      tzinfo (~> 0.3.37)
    atomic (1.1.14)
    benchmark-ips (1.2.0)
    i18n (0.6.9)
    jbuilder (2.0.2)
      activesupport (>= 3.0.0)
      multi_json (>= 1.2.0)
    minitest (4.7.5)
    multi_json (1.8.4)
    oj (2.5.4)
    rabl (0.9.3)
      activesupport (>= 2.3.14)
    thread_safe (0.1.3)
      atomic
    tzinfo (0.3.38)

PLATFORMS
  ruby

DEPENDENCIES
  activesupport
  benchmark-ips
  jbuilder
  oj
  rabl

Result(from the revesion d0696b8d):

                                user     system      total        real
Jbuilder(single object)     1.040000   0.000000   1.040000 (  1.045209)
Rabl(single object)         2.350000   0.000000   2.350000 (  2.368760)
Jbuilder(collection)        2.780000   0.000000   2.780000 (  2.798979)
Rabl(collection)           12.910000   0.020000  12.930000 ( 12.972485)

updated the code/gems and ran the above again(higher is better):

$ bundle exec ruby benchmark.rb 
Calculating -------------------------------------
Jbuilder(single obj)      2932 i/100ms
    Rabl(single obj)       870 i/100ms
Jbuilder(collection)       984 i/100ms
    Rabl(collection)       273 i/100ms
-------------------------------------------------
Jbuilder(single obj)    42435.5 (±5.0%) i/s -     214036 in   5.058724s
    Rabl(single obj)    10409.0 (±5.7%) i/s -      52200 in   5.031122s
Jbuilder(collection)    11913.3 (±4.0%) i/s -      60024 in   5.046583s
    Rabl(collection)     2817.2 (±10.2%) i/s -      13923 in   5.017393s

Ruby version:

$ ruby -v
ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-linux]

jbuilder is almost 4 times faster than rabl.

I wonder if these benchmarks still hold.