results.txt

~/Desktop > ruby --version
ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin14]

~/Desktop > ruby ./concat_benchmark.rb 
Calculating -------------------------------------
       Interpolation    81.309k i/100ms
        Array + join    65.714k i/100ms
String concatenation    62.816k i/100ms
     String mutation    68.529k i/100ms
-------------------------------------------------
       Interpolation      1.843M (± 6.0%) i/s -      9.188M
        Array + join      1.218M (± 5.8%) i/s -      6.111M
String concatenation      1.087M (± 5.1%) i/s -      5.465M
     String mutation      1.248M (± 5.0%) i/s -      6.236M

string.rb

#!/usr/bin/env ruby

require 'benchmark/ips'

STRING = "hello there".freeze

Benchmark.ips do |x|
  x.report("Interpolation") do
    "#{STRING}-#{STRING}-#{STRING}"
  end

  x.report("Array + join") do
    [STRING, STRING, STRING].join("-")
  end

  x.report("String concatenation") do
    STRING + "-" + STRING + "-" + STRING
  end

  x.report("String mutation") do
    str = ""
    str << STRING
    str << "-"
    str << STRING
    str << "-"
    str << STRING
  end
end