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Ever wonder which is the fastest way to concatenate strings in Ruby?

No? Too bad!

From this:

require 'benchmark'
Benchmark.bm(20) do |x|
  x.report ('<<') do
    1_000_000.times do
      one = 'one'
      two = 'two'
      three = 'three'
      y = one << two << three
    end
  end
  x.report('+') do
    1_000_000.times do
      one = 'one'
      two = 'two'
      three = 'three'
      y = one + two + three
    end
  end
  x.report('#{one}#{two}#{three}') do
    1_000_000.times do
      one = 'one'
      two = 'two'
      three = 'three'
      y = "#{one}#{two}#{three}"
    end
  end
  x.report('one#{two}#{three}') do
    1_000_000.times do
      two = 'two'
      three = 'three'
      y = "one#{two}#{three}"
    end
  end
  x.report('onetwo#{three}') do
    1_000_000.times do
      three = 'three'
      y = "onetwo#{three}"
    end
  end
end

Comes this:

                           user     system      total        real
<<                     4.580000   0.000000   4.580000 (  4.579776)
+                      5.720000   0.000000   5.720000 (  5.815782)
#{one}#{two}#{three}   5.180000   0.000000   5.180000 (  5.185434)
one#{two}#{three}      3.920000   0.000000   3.920000 (  3.917942)
onetwo#{three}         2.610000   0.000000   2.610000 (  2.617674)

Thus proving a two things:

1. Use << for concatenation. It doesn’t make an intermediate copy, unlike +.
2. If you need to place a string variable inside a chunk of static text, it’s far faster to use interpreted string literals than to concatenate string variables.

Yup.

This entry was posted on Tuesday, April 18th, 2006 at 7:11pm and is filed under Programming, Ruby and Rails. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.