benchmark_access.rb

require 'benchmark/ips'

class A
  def initialize
    @attributes = { :foo => 1 }
  end

  def foo
    @attributes[:foo]
  end
end

class B
  def initialize
    @attributes = { 'foo' => 1 }
  end

  def foo
    @attributes['foo']
  end
end

a = A.new
b = B.new

Benchmark.ips do |r|
  r.report('symbol') { a.foo }
  r.report('string') { b.foo }
end

results.txt

$ ruby benchmark_access.rb
Calculating -------------------------------------
              symbol     49716 i/100ms
              string     45447 i/100ms
-------------------------------------------------
              symbol  2495270.4 (±4.5%) i/s -   12478716 in   5.014637s
              string  1645124.6 (±8.2%) i/s -    8180460 in   5.012095s