Benchmark instance variable vs delegation

benchmark_instance_var_vs_delegate.rb

require 'benchmark'
require 'active_support/all'

Source = Struct.new(:value, keyword_init: true)

class InstanceVarTest
  attr_reader :source, :value

  def initialize(source)
    @source = source
    @value = source.value
  end
end

# Rails delegate has an extra local var assignment so it can yield improved
# error messages
class RailsDelegateTest
  attr_reader :source
  delegate :value, to: :source

  def initialize(source)
    @source = source
  end
end

class ManualDelegateTest
  attr_reader :source

  def initialize(source)
    @source = source
  end

  def value
    source.value
  end
end

source = Source.new(value: "value")

n = 100_000
Benchmark.bmbm(15) do |x|
  x.report("reader")          { n.times { InstanceVarTest.new(source).value } }
  x.report("rails delegate")  { n.times { RailsDelegateTest.new(source).value } }
  x.report("manual delegate") { n.times { ManualDelegateTest.new(source).value } }
end

# >>                       user     system      total        real
# >> reader            0.017031   0.000017   0.017048 (  0.017064)
# >> rails delegate    0.023334   0.000005   0.023339 (  0.023340)
# >> manual delegate   0.016949   0.000005   0.016954 (  0.016954)