Hash key lookup performance vs local variable.

benchmark.rb

require 'benchmark'
require 'stringio'

sizes = [10,100,1000,10000]

def measure(&block)
  puts Benchmark.measure { 100000.times(&block) }
end

sizes.each do |size|
  
  fake_io = StringIO.new
  other_fake_io = StringIO.new

  hash = (1..size).inject({}) { |h, k| h[k] = "value #{k}"; h }
  puts "Measuring for hash size #{size}"

  puts "Key lookup"
  measure do
    5.times { fake_io.puts hash[5] }
  end

  puts "Var stash"
  measure do
    var = hash[5]
    5.times { other_fake_io.puts var }
  end
end

output.text

Measuring for hash size 10
Key lookup
  0.310000   0.010000   0.320000 (  0.310216)
Var stash
  0.290000   0.000000   0.290000 (  0.294578)

Measuring for hash size 100
Key lookup
  0.320000   0.000000   0.320000 (  0.319517)
Var stash
  0.310000   0.010000   0.320000 (  0.317231)

Measuring for hash size 1000
Key lookup
  0.310000   0.000000   0.310000 (  0.315608)
Var stash
  0.300000   0.010000   0.310000 (  0.303324)

Measuring for hash size 10000
Key lookup
  0.390000   0.000000   0.390000 (  0.412032)
Var stash
  0.320000   0.010000   0.330000 (  0.326415)