Quick benchmark of string appending

bench.out

Rehearsal ------------------------------------------------------------------
interpol                         0.218000   0.000000   0.218000 (  0.218013)
plus                             0.156000   0.000000   0.156000 (  0.158009)
append                           0.390000   0.000000   0.390000 (  0.386022)
const interpol                   0.203000   0.000000   0.203000 (  0.193011)
const plus                       0.218000   0.000000   0.218000 (  0.231013)
const append                     0.203000   0.000000   0.203000 (  0.196011)
--------------------------------------------------------- total: 1.388000sec

                                     user     system      total        real
interpol                         0.219000   0.000000   0.219000 (  0.213012)
plus                             0.156000   0.000000   0.156000 (  0.156009)
append                           0.374000   0.000000   0.374000 (  0.383022)
const interpol                   0.203000   0.000000   0.203000 (  0.191011)
const plus                       0.218000   0.000000   0.218000 (  0.224013)
const append                     0.187000   0.000000   0.187000 (  0.193011)

bench.rb

require 'benchmark'

REP = 1_000_000
a = "foo".freeze
b = "bar".freeze

Benchmark.bmbm 30 do |x|
  x.report "interpol" do
    REP.times { "#{a}#{b}" }
  end

  x.report "plus" do
    REP.times { a + b }
  end

  x.report "append" do
    REP.times { a.dup << b }
  end

  x.report "const interpol" do
    REP.times { "foo#{b}" }
  end

  x.report "const plus" do
    REP.times { 'foo' + b }
  end

  x.report "const append" do
    REP.times { 'foo' << b }
  end
end