From: Robert Klemme <bob.news@...>
Date: 2005-08-05T03:11:06+09:00
Subject: Re: Defining regexp's and variables set by them

Robert Klemme <bob.news@gmx.net> wrote:
> Garance A Drosehn <drosihn@gmail.com> wrote:
>> On 8/2/05, Caleb Clausen <vikkous@gmail.com> wrote:
>>> On 8/1/05, Garance A Drosehn <drosihn@gmail.com> wrote:
>>>> Does ruby keep the compiled-code for a method after
>>>> the method is finished?
>>>
>>> Uhhh, it's nowhere near that fancy. Ruby is a fairly traditional
>>> interpreter, without even bytecode compilation. That's why it's
>>> so slow.
>>
>> That is what I expected.  So I'm back to wishing to have one
>> method which creates all the Regexp.new's as @@variables,
>> and then I can reference those compiled Regexp's in other
>> methods for that class.
>
> Performance does not differ much between a regexp in place and a
> regexp compiled once and stored in a variable or constant (assuming no
> interpolation is used or interpolation with "o" is used - otherwise
> both scenarios have different semantics anyway and can't be
> compared).  Ruby *has* been optimized to make in place regexps
> efficient - there is no recompilation of the regexp on every pass.
>
> You can try it out with the attached script.  Using several
> invocations either of the two is faster
>
>                user     system      total        real
> direct      0.312000   0.000000   0.312000 (  0.305000)
> compiled    0.313000   0.000000   0.313000 (  0.306000)
>
>                user     system      total        real
> direct      0.313000   0.000000   0.313000 (  0.319000)
> compiled    0.297000   0.000000   0.297000 (  0.305000)
>
>> Almost.  I was saying that I *wanted* to have them distant,
>> because the result is more readable (for what I'm doing, IMO),
>> and for the efficiency benefit.
>
> As I said there is no such thing as an efficiency benefit in using
> "remote" regexps.
>
>>  This may seem weird, but most
>> of the regexp's that I'm talking about are three or four full lines
>> long, complete with a few regexp tricks that take a few more
>> lines of comments to explain what the regexp is doing.  The
>> case-statement is *much* more readable if the regexp's are
>> separated from the case statement.
>
> I'd stick with the readability argument and forget about the
> performance here.  The question is, does the code become more
> readable by moving the regexps out of the case statement?  I don't
> know your code but I'd say it's not automatically so.
>
> Kind regards
>
>    robert

Sorry, I forgot the attachment.  Here's the script:

    robert


require 'benchmark'

REPEAT = 10000

RX = /foo/

TEXT = <<EOS
akdnhkaj dahdk ahda da#dada
da
dopakdjalkjdlak djadklasd
adasklfoodk�asjhdjkasdha
dadjkadjkashdjkasd#
aajdhkasjdjkfooashd
aldaksjhdjasd
EOS

Benchmark.bmbm 10 do |b|
  b.report "direct" do
    REPEAT.times { TEXT.scan(/foo/o) {|m| m + "x"} }
  end

  b.report "compiled" do
    REPEAT.times { TEXT.scan(RX) {|m| m + "x"} }
  end
end