instance-bm.rb

require 'benchmark/ips'

class SelfRuby
  attr_accessor :foo
  def initialize
    self.foo = 1
  end
end

# SLOWEST!
class InstRuby
  def initialize
    @foo = 1
  end

  def foo
    @foo
  end
end

class CombRuby
  attr_accessor :foo
  def initialize
    @foo = 1
  end
end

a = SelfRuby.new
b = InstRuby.new
c = CombRuby.new

Benchmark.ips do |x|
  x.report 'self.foo attr access' do
    a.foo
  end

  x.report '@foo no attr' do
    b.foo
  end

  x.report '@foo w/ attr' do
    c.foo
  end

  x.compare!
end

# › ruby bm.rb
# Warming up --------------------------------------
# self.foo attr access   323.704k i/100ms
# @foo no attr   313.221k i/100ms
# @foo w/ attr   324.119k i/100ms
# Calculating -------------------------------------
# self.foo attr access     11.303M (± 2.6%) i/s -     56.648M in   5.015020s
# @foo no attr     10.319M (± 2.4%) i/s -     51.681M in   5.011602s
# @foo w/ attr     11.484M (± 2.1%) i/s -     57.693M in   5.026025s
# 
# Comparison:
#   @foo w/ attr: 11483943.6 i/s
# self.foo attr access: 11303406.2 i/s - same-ish: difference falls within error
# @foo no attr: 10318936.3 i/s - 1.11x  slower