From a discussion at http://stackoverflow.com/questions/1836467/is-there-a-performance-gain-in-using-single-quotes-vs-double-quotes-in-ruby

Ruby Concat vs. Interpolate

require 'benchmark'
n = 1000000
m = n.to_s
Benchmark.bm do |x|
  x.report("assign single") { n.times do; c = 'a string'; end}
  x.report("assign double") { n.times do; c = "a string"; end}
  x.report("assign interp") { n.times do; c = "a #{n} string"; end}
  x.report("concat single") { n.times do; 'a ' + n.to_s + ' string b ' + n.to_s + ' string'; end}
  x.report("concat double") { n.times do; "a " + n.to_s + " string b " + n.to_s + " string"; end}
  x.report("concat interp") { n.times do; "a #{n} string b #{n} string"; end}
  x.report("single optim") { n.times do; 'a ' + m + ' string b ' + m + ' string'; end}
  x.report("double optim") { n.times do; "a " + m + " string b " + m + " string"; end}
  x.report("interp optim") { n.times do; "a #{m} string b #{m} string"; end}
end

1.9.2
-----
                 user     system      total        real
assign single  0.170000   0.000000   0.170000 (  0.165743)
assign double  0.160000   0.000000   0.160000 (  0.164564)
assign interp  0.650000   0.010000   0.660000 (  0.716917)
concat single  1.660000   0.000000   1.660000 (  1.674781)
concat double  1.680000   0.000000   1.680000 (  1.695005)
concat interp  1.320000   0.010000   1.330000 (  1.321017)
single optim   1.240000   0.000000   1.240000 (  1.245957)
double optim   1.210000   0.000000   1.210000 (  1.218838)
interp optim   0.860000   0.000000   0.860000 (  0.854629)




1.8.7
-----
                 user     system      total        real
assign single  0.250000   0.000000   0.250000 (  0.250248)
assign double  0.240000   0.000000   0.240000 (  0.244231)
assign interp  1.220000   0.010000   1.230000 (  1.287550)
concat single  3.100000   0.010000   3.110000 (  3.246304)
concat double  3.040000   0.010000   3.050000 (  3.153448)
concat interp  1.970000   0.000000   1.970000 (  1.987011)
single optim   2.040000   0.010000   2.050000 (  2.138786)
double optim   2.000000   0.000000   2.000000 (  2.021183)
interp optim   0.940000   0.000000   0.940000 (  0.947649)