From: Peter Vandenabeele <peter@...>
Date: 2012-02-03T08:33:26+09:00
Subject: Re: Basic Ruby performance

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On Fri, Feb 3, 2012 at 12:20 AM, Ryan Davis <ryand-ruby@zenspider.com>wrote:

>
> On Feb 2, 2012, at 14:55 , Dmitry Nikiforov wrote:
>
> > Here's another example with significantly bigger performance difference:
> >
> > Ruby:
> >
> > s = "This is a test string"
> >
> > re = Regexp.new( / test / )
> >
> > for a in 0..1E7
> >        re.match( s )
> > end
> >
> > Perl:
> >
> > my $s = "This is a test string";
> >
> > for my $a ( 0..1E7 ) {
> >       $s =~ / test /;
> > }
> >
> > Perl takes about 1.5 seconds to execute this, while Ruby takes a
> > whopping 16!!! :((( I have a very strong feeling that I didn't compile
> > Ruby properly - there can't be such a huge difference in regexp matching
> > :(
>
> It's all the parens, whitespace, and use of tabs that slows ruby down:
>

Euhmmm, I doubt that ...


>
> # takes 26.6 seconds on my laptop:
>
> s = "This is a test string"
>
> re = Regexp.new( / test / )
>
> for a in 0..1E7
>       re.match( s )
> end
>
> # takes 8.67 seconds on my laptop:
>
> s = "This is a test string"
>
> for a in 0..1E7
>  s =~ / test /
> end
>

The same "formatted" code with just replacing re.match( s) by
s =~ /test/ also causes the same change from 22 to 7 seconds
on my system (with the same formatting, spaces, etc.).

I rather expect it's because

`match` and `=~`  do quite different things ...

`match` returns a complete MatchData object

`=~` returns the index (position) of the first match

017:0>       re.match( s )
=> #<MatchData " test ">
018:0>       s =~ /test/
=> 10

<speculation>
Maybe (speculation) the MatchData object takes more
dynamic Object allocation and thus more calls to the GC ?
</speculation>

HTH,

Peter

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