From: Kornelius Kalnbach <murphy@...>
Date: 2010-03-05T06:08:51+09:00
Subject: [ruby-core:28490] Re: [Feature #905] Add String.new(fixnum) to preallocate large buffer

On 04.03.10 21:08, caleb clausen wrote:
> If String#<< is really O(1), there would seem to be little reason to
> change anything. I still want to investigate this myself when I get a
> chance.
O(n), where n is the size of the appended string.

But I think it's always worth to look into speedups even if we can't
expect to change the complexity class. The O-factor may not interesting
to theorists, but it matters greatly to programmers. JRuby, for example,
concats strings almost twice as fast in this benchmark:

require 'benchmark'

N = 10_000_000
Benchmark.bm 20 do |results|
  results.report 'loop' do
    N.times { }
  end
  results.report "'' <<" do
    s = ''
    N.times { s << '.' << 'word' }
  end
end

ruby19 string_buffer.rb
                          user     system      total        real
loop                  1.240000   0.010000   1.250000 (  1.255154)
'' <<                 5.820000   0.060000   5.880000 (  5.889959)

jruby string_buffer.rb
                          user     system      total        real
loop                  0.584000   0.000000   0.584000 (  0.488000)
'' <<                 2.900000   0.000000   2.900000 (  2.900000)

So, there is room for optimization somewhere.

[murphy]