Ruby single quotes vs. double quotes

benchmark.rb

require "benchmark"

Benchmark.bm(7) do |bench|
  bench.report("single") do
    1_000_000.times do
      'This is a string of substantial length. I doubt you will have many string
      literals in your code that are longer than this, but if there are actually
      costs to parsing double quoted strings this should exacerbate that.'
    end
  end

  bench.report("double") do
    1_000_000.times do
      "This is a string of substantial length. I doubt you will have many string
      literals in your code that are longer than this, but if there are actually
      costs to parsing double quoted strings this should exacerbate that."
    end
  end
end

results.md

Here are the results of the above benchmark running against three different Ruby VMs.

ruby 1.9.2p320 (2012-04-20 revision 35421) [x86_64-darwin11.4.0]

             user     system      total        real
single   0.170000   0.000000   0.170000 (  0.171696)
double   0.170000   0.000000   0.170000 (  0.171394)

ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.4.0]

              user     system      total        real
single    0.190000   0.000000   0.190000 (  0.189292)
double    0.180000   0.000000   0.180000 (  0.184996)

jruby 1.7.0.preview1 (ruby-1.9.3-p203) (2012-05-19 00c8c98) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_35) [darwin-x86_64-java]

              user     system      total        real
single    0.420000   0.010000   0.430000 (  0.221000)
double    0.240000   0.010000   0.250000 (  0.118000)

As you can see, double quotes are actually faster in all three VMs. They are twice as fast in JRuby but only marginally faster in the two CRuby VMs. I don't have Rubinius on hand or I'd test that as well.

So, there you have it. Double quotes interpolate strings easily, support several nifty escape sequences like \n and \t, and for whatever reason they're faster than their counterpart. Maybe because there's 2X the quotes!

ruby 2.4.1
if double quotes has interpolation

Benchmark.bm(7) do |bench|
  bench.report("single") do
    1_000_000.times do
      'This is a string of substantial length. I doubt you will have many string
      literals in your code that are longer than this, but if there are actually
      costs to parsing double quoted strings this should exacerbate that.'
    end
  end

  bench.report("double") do
    1_000_000.times do |i|
      "|i| This is a string of substantial length. I doubt you will have many string
      literals in your code that are longer than this, but if there are actually
      costs to parsing double quoted strings this should exacerbate that."
    end
  end
end

          user     system      total        real
          user     system      total        real

single 0.070000 0.000000 0.070000 ( 0.071082)
double 0.080000 0.000000 0.080000 ( 0.079633)