[ruby-core:28545] [Feature #905] Add String.new(fixnum) to preallocate large buffer

Issue #905 has been updated by _ wanabe.


Hi, 

>  opt = false
>  1000.times do
>    s = ""
>    s.buffer(opt ? 100_001 : 100)
>    x = "x" * 1000
>    100.times { s << x }
>  end
>
> takes 0.115 sec. when opt is false, 0.130 sec. when opt is true.

I tried too.
Interestingly, it gets faster on my environment.

$ cat test.rb
require 'benchmark'
opt = ARGV[0]
list = Array.new(10) do
  Benchmark.realtime do
    1000.times do
      s = ""
      s.buffer(opt ? 100_001 : 100)
      x = "x" * 1000
      100.times { s << x }
    end
  end
end
list.sort!
p list.first, list.last

$ ./ruby -v -Ilib test.rb opt
ruby 1.9.2dev (2010-03-07 trunk 26843) [i386-mingw32]
0.1780099868774414
0.18601107597351074

$ ./ruby -v -Ilib test.rb
ruby 1.9.2dev (2010-03-07 trunk 26843) [i386-mingw32]
0.21401190757751465
0.22301316261291504

But, I guess, the patch may not work as expected in some cases.
Some methods (String#succ!, sub!, []=, and so on) can let CAPA shrink.
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http://redmine.ruby-lang.org/issues/show/905

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