Performance comparison between hash lookup and case lookup

hash_vs_case.rb

MAPPING = {
  a: 1,
  b: 2,
  c: 3,
  d: 4,
  e: 5,
  f: 6,
}.freeze

def method1(key)
  MAPPING[key]
end

def method2(key)
  case key
  when :a then 1
  when :b then 2
  when :c then 3
  when :d then 4
  when :e then 5
  when :f then 6
  end
end

def method3(key)
  mapping = {
    a: 1,
    b: 2,
    c: 3,
    d: 4,
    e: 5,
    f: 6,
  }
  mapping[key]
end

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('method1') { method1(:f) }
  x.report('method2') { method2(:f) }
  x.report('method3') { method3(:f) }

  x.compare!
end

__END__

Warming up --------------------------------------
             method1     1.409M i/100ms
             method2     1.403M i/100ms
             method3   785.691k i/100ms
Calculating -------------------------------------
             method1     14.498M (± 1.4%) i/s -     73.245M in   5.053246s
             method2     14.113M (± 3.7%) i/s -     71.536M in   5.076314s
             method3      8.912M (±10.1%) i/s -     43.999M in   5.052516s

Comparison:
             method1: 14497516.1 i/s
             method2: 14112908.5 i/s - same-ish: difference falls within error
             method3:  8911587.0 i/s - 1.63x  (± 0.00) slower