Static vs Dynamic underscore

static_vs_dynamic_underscore.rb

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  gem "activesupport"
  gem "benchmark-ips", require: "benchmark/ips"
end

require "active_support/all"

FOOBAR = "foo_bar".freeze
MAPPING = {
  "FooBar" => FOOBAR,
  "fooBar" => FOOBAR,
  "Foo_Bar" => FOOBAR
}.freeze

Benchmark.ips do |x|
  x.warmup = 20
  x.report("underscore") do
    "FooBar".underscore
    "fooBar".underscore
    "Foo_Bar".underscore
  end
  x.report("mapping") do
    MAPPING["FooBar"]
    MAPPING["fooBar"]
    MAPPING["Foo_Bar"]
  end
  x.compare!
end
__END__

Warming up --------------------------------------
          underscore     6.790k i/100ms
             mapping   150.724k i/100ms
Calculating -------------------------------------
          underscore     77.864k (± 2.2%) i/s -    393.820k in   5.060335s
             mapping      3.660M (± 2.9%) i/s -     18.388M in   5.029111s

Comparison:
             mapping:  3659726.5 i/s
          underscore:    77863.6 i/s - 47.00x slower