benchmark.rb

#!/usr/bin/env ruby

require 'inline'
require 'benchmark'

hash = {foo: "bar"}

n = 10_000_000

Benchmark.bm() do |x|
  x.report("hash[]")        { n.times { hash[:foo] } }
  x.report("hash.has_key?") { n.times { hash.has_key? :foo } }
end

benchmark.txt

maasha@mel:~$ ./benchmark.rb
       user     system      total        real
hash[]  1.100000   0.000000   1.100000 (  1.111618)
hash.has_key?  1.360000   0.000000   1.360000 (  1.364842)
maasha@mel:~$ rbx benchmark.rb
       user     system      total        real
hash[]  2.341919   0.019072   2.360991 (  2.272809)
hash.has_key?  1.915534   0.002146   1.917680 (  1.860527)