Useless Ruby StringBuilder

A little while ago, I wrote a StringBuilder class in Ruby in my lunch break, roughly based on the one in the .NET Framework, but simpler. I have known for a while that using StringBuilder is a much quicker way of concatening strings than just using +. I'm talking about C# indeed, and expect VB.Net to need the same.

I'm still fairly new to Ruby, so I thought I would give it a go there. I didn't find a StringBuilder class available, so I wrote a simple one. I looked a bit further and found there are two ways to concatenate strings in Ruby, using + and <<.

I added a bit of benchmarking code, and lo and behold, my StringBuilder class is lightning fast compared to the + method....

[with 100,000 iterations]
                  user     system      total        real
stringbuilder:  0.172000   0.000000   0.172000 (  0.172000)
string<<:       0.094000   0.000000   0.094000 (  0.094000)
string+=:      14.703000   3.860000  18.563000 ( 18.734000)

But it is obvious << is a much better choice. Blimey, look at that. That's about 200 times faster than += ! No wonder there is no StringBuilder class provided with the Ruby core.

[with 1,000,000 iterations]
                  user     system      total        real
stringbuilder:  1.610000   0.031000   1.641000 (  1.656000)
string<<:       1.156000   0.000000   1.156000 (  1.156000)

[with 10,000,000 iterations]
                  user     system      total        real
stringbuilder: 17.672000   0.140000  17.812000 ( 17.953000)
string<<:      10.047000   0.047000  10.094000 ( 10.343000)

I had to remove the += case in these last two reports as my script wouldn't have returned before my lunch break was over!

require "benchmark"
include Benchmark

class Stringbuilder
  def initialize(s)
    @s=[s]
  end
  
  def <<(s)
    @s << s
  end
  
  def to_s
    @s.join("")
  end
end

TESTS=100000

bm(14) do |test|
  test.report("stringbuilder:") do
    x=Stringbuilder.new("bla")
    TESTS.times { |i|
      x << "x"
    }
    z = x.to_s
  end
  test.report("string<<:") do
    y="bla"
    TESTS.times { |i|
      y << "x"
    }
    z = y.to_s
  end
  test.report("string+=:") do
    y="bla"
    TESTS.times { |i|
      y += "x"
    }
    z = y.to_s
  end
end