From: Jeremy Bopp <jeremy@...>
Date: 2012-02-03T13:08:12+09:00
Subject: Re: Basic Ruby performance

On 02/02/2012 09:47 PM, Josh Cheek wrote:
> On Thu, Feb 2, 2012 at 8:57 PM, Jeremy Bopp <jeremy@bopp.net> wrote:
> 
>>
>> Try a similar change to the other looping variations that have been
>> discussed and see if and how much they may improve.  For me I didn't
>> really see any difference between using re as above or using the simple
>> regexp directly; however, the code was almost an order of magnitude
>> slower when I replaced the comparison as follows:
>>
>>  s =~ / test#{} /
>>
>> It seems that Ruby is smart enough to see that the simple regexp will
>> never need to be re-evaluated.  The regexp used above must force that
>> optimization off because #{} while constantly evaluated to the empty
>> string is technically dynamic, thus the regexp needs to be re-evaluated
>> in every iteration of the loop.
>>
>>
> The o flag tells Ruby to only interpolate the first time, and then cache
> the regex
> 
> s =~ / test#{} /o

Thanks for the tip! :-)  Still, sprinkling that option around might
cause more confusion than assigning the regexp to a constant and using
that reference instead.  Someone reading your code later may overlook
the dangling "o" on a complex regexp and be left wondering why the
interpolation isn't happening like they expect.

I guess it really depends on the scope of your task though.

-Jeremy