Benchmark how to look up a class from string in Ruby

.ruby-version

2.3

README.md

Benchmark how to look up a class from string in Ruby

Rescue NameError or ask if the constant is defined first?

Tested in Ruby 2.3 on OS X

$ bundle
...
$ bundle exec ruby benchmark.rb
Warming up --------------------------------------
undefined const with rescue
                        98.256k i/100ms
undefined const by asking first
                        26.705k i/100ms
Calculating -------------------------------------
undefined const with rescue
                          1.787M (± 2.7%) i/s -      8.941M in   5.008211s
undefined const by asking first
                        337.107k (± 3.0%) i/s -      1.709M in   5.074571s

Comparison:
undefined const with rescue:  1786652.0 i/s
undefined const by asking first:   337106.6 i/s - 5.30x  slower

Warming up --------------------------------------
defined const with rescue
                        88.743k i/100ms
defined const by asking first
                       117.461k i/100ms
Calculating -------------------------------------
defined const with rescue
                          1.442M (± 2.9%) i/s -      7.277M in   5.050590s
defined const by asking first
                          2.453M (± 3.6%) i/s -     12.333M in   5.034416s

Comparison:
defined const by asking first:  2453319.7 i/s
defined const with rescue:  1442062.0 i/s - 1.70x  slower

benchmark.rb

require "benchmark/ips"

class ForBenchmark1; end
class ForBenchmark2; end

def get_const_by_asking_first(const_name)
  Kernel.const_defined?(const_name) && Kernel.const_get(const_name)
end

def get_const_with_rescue(const_name)
  Kernel.const_get(const_name)
rescue NameError # Makes it very hard to discover typos in code
end

# Ensure behavior before benchmarking
raise "Fail!" unless ForBenchmark1 == get_const_by_asking_first("ForBenchmark1")
raise "Fail!" unless ForBenchmark2 == get_const_with_rescue("ForBenchmark2")
raise "Fail!" if get_const_by_asking_first("Undefined1")
raise "Fail!" if get_const_with_rescue("Undefined2")

# Benchmark with undefined constants
Benchmark.ips do |x|
  x.report("undefined const with rescue") do
    get_const_by_asking_first("Undefined1")
  end

  x.report("undefined const by asking first") do
    get_const_with_rescue("Undefined2")
  end

  x.compare!
end

# Benchmark with defined constants
Benchmark.ips do |x|
  x.report("defined const with rescue") do
    get_const_by_asking_first("ForBenchmark1")
  end

  x.report("defined const by asking first") do
    get_const_with_rescue("ForBenchmark2")
  end

  x.compare!
end

Gemfile

source "https://rubygems.org"

gem "benchmark-ips"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    benchmark-ips (2.7.2)

PLATFORMS
  ruby

DEPENDENCIES
  benchmark-ips

BUNDLED WITH
   1.13.3