instance_variable_get performance

instance_variabe_get.rb

require 'benchmark/ips'

class Test
  def intitialize
    @ivar = 'test'
  end

  def direct
    @ivar
  end

  IVAR_NAME = "@ivar"
  def hoist_ivar_name
    instance_variable_get IVAR_NAME
  end

  def instance_variable_get_symbol
    instance_variable_get :"@ivar"
  end

  def instance_variable_get_frozen
    instance_variable_get('@ivar'.freeze)
  end

  def instance_variable_get_frozen_symbol
    instance_variable_get('@ivar'.freeze.to_sym)
  end
end

Benchmark.ips do |benchmark|

  instance = Test.new
  benchmark.report("direct") {instance.direct}
  benchmark.report("hoist_ivar_name") {instance.hoist_ivar_name}
  benchmark.report("ivar get symbol") {instance.instance_variable_get_symbol}
  benchmark.report("ivar get frozen") {instance.instance_variable_get_frozen}
  benchmark.report("ivar get frozen sym") {instance.instance_variable_get_frozen_symbol}
end

jruby 9.0.3.0 with some optimizations turned on:

tobi@airship ~ $ ruby --server -Xcompile.invokedynamic=true ivar_get.rb 
Calculating -------------------------------------
              direct    91.369k i/100ms
     hoist_ivar_name   112.476k i/100ms
     ivar get symbol   113.564k i/100ms
     ivar get frozen   160.592k i/100ms
 ivar get frozen sym   158.691k i/100ms
-------------------------------------------------
              direct     10.812M (±19.7%) i/s -     50.162M
     hoist_ivar_name      5.402M (±28.8%) i/s -     24.070M
     ivar get symbol     10.310M (±12.7%) i/s -     49.968M
     ivar get frozen      3.163M (± 5.0%) i/s -     15.899M
 ivar get frozen sym      5.428M (±17.5%) i/s -     26.025M

ruby 2.6.0 (and newer hardware)

Warming up --------------------------------------
              direct     2.415M i/100ms
     hoist_ivar_name     1.101M i/100ms
     ivar get symbol     1.821M i/100ms
     ivar get frozen     1.136M i/100ms
 ivar get frozen sym     1.116M i/100ms
Calculating -------------------------------------
              direct     24.245M (± 0.9%) i/s -    123.177M in   5.080832s
     hoist_ivar_name     10.951M (± 0.6%) i/s -     55.056M in   5.027655s
     ivar get symbol     18.150M (± 1.0%) i/s -     91.067M in   5.017868s
     ivar get frozen     11.174M (± 3.1%) i/s -     56.781M in   5.086655s
 ivar get frozen sym     10.308M (± 5.6%) i/s -     52.456M in   5.106387s