attr_reader vs instance var

benchmark.rb

require 'benchmark/ips'

class Foo
  attr_reader :test

  def initialize(test)
    @test = test
  end

  def read
    test
  end
end

class Bar
  def initialize(test)
    @test = test
  end

  def read
    @test
  end
end

Benchmark.ips do |x|
  x.config(time: 10)
  foo = Foo.new('lalala')
  bar = Bar.new('lalala')
  x.report('attr') { foo.read }
  x.report('instance') { bar.read }
  x.compare!
end

Calculating -------------------------------------
                attr   140.015k i/100ms
            instance   140.783k i/100ms
-------------------------------------------------
                attr      7.790M (± 8.0%) i/s -     77.428M
            instance      7.864M (±11.8%) i/s -     77.290M

Comparison:
            instance:  7864065.9 i/s
                attr:  7789875.8 i/s - 1.01x slower