String prepend FTW

bench.rb

require 'benchmark'
require 'benchmark/ips'

Benchmark.ips do |x|
  x.report("String::prepend") { "foo".prepend "tmp/" }
  x.report("File.join") { File.join "tmp", "foo" }
end
puts
Benchmark.bm do |x|
  x.report("String::prepend") { 1000000.times{"foo".prepend "tmp/"} }
  x.report("File.join") { 1000000.times{File.join "tmp", "foo"} }
end

results.txt

Calculating -------------------------------------
     String::prepend     86847 i/100ms
           File.join     57009 i/100ms
-------------------------------------------------
     String::prepend  2287790.4 (±7.2%) i/s -   11376957 in   5.005150s
           File.join  1189393.1 (±3.0%) i/s -    5985945 in   5.037805s

       user     system      total        real
String::prepend  0.350000   0.000000   0.350000 (  0.352643)
File.join  0.760000   0.000000   0.760000 (  0.759962)