Re: StringBuilder Extension: IsQuotedBy

perf, strings and loops

I have developed a few .NET based parsers during the last few years and here are som fast comments:

1. avoid creating objects, all kinds of objects are "really expensive" to create, especially in loops. gc:s generally aren't an issue when parsing, unless parsing HUGE documents, a small parser will have completed before the gc kicks in.

2. avoid virtual calls and delegates; both are great for flexibility but slows your code down considerably when executed in tight parse-loops.

3. regexp really rocks if you are looking for flexibilty; in those cases where flexibility is more important then speed regexp is really the perfect match, but if you are working on a small, well-defined and really fast parser don't even think about regexp.

(1), (2) and (3) all trade performance against readability and maintainability; I recomend regexp for all "slow" cases but if you really are looking for performance it isn't a good solution. If a parse case is "slow" or "fast" really depend on your development task, but be adviced, developing complex parsers without regexp isn't for the faint-hearted =)

regards,
  Daniel

 ________________________________________
From: Discussion of development on the .NET platform using any managed              language [[email protected]] On Behalf Of Brady Kelly [[email protected]]
Sent: Thursday, February 14, 2008 8:58 AM
To: [email protected]
Subject: Re: [DOTNET-CLR] StringBuilder Extension: IsQuotedBy

Probably, but I always get uneasy creating strings in loops, and this was
just the culmination of my paranoia, fuelled by an evil combination of
caffeine and fatigue.

>
> Isn't a ToString() with a regexp more efficient?
>
>         FB
>
> > I was playing around with avoiding, at all costs, creating surplus
> strings,
> > and came up with the following method to see if a StringBuilder, that
> I use
> > for each of a collection of string fields, is surrounded by a certain
> > string, e.g. double quotes.  I was just wondering if this is an
> efficiant
> > way of doing it:
> >
> >
> >
> >         public static bool IsQuotedBy(this StringBuilder sb, string
> > quoteString)
> >
> >         {
> >
> >             // Check if the first characters match the quote string.
> >
> >             for (int i = 0; i < quoteString.Length; i++)
> >
> >             {
> >
> >                 if (sb[i] != quoteString[i])
> >
> >                 {
> >
> >                     return false;
> >
> >                 }
> >
> >             }
> >
> >
> >
> >             // Check if the last characters match the quote string.
> >
> >             for (int i = sb.Length - quoteString.Length; i <
> sb.Length; i++
> > )
> >
> >             {
> >
> >                 int qsIndex = 0;
> >
> >                 if (sb[i] != quoteString[qsIndex++])
> >
> >                 {
> >
> >                     return false;
> >
> >                 }
> >
> >             }
> >
> >
> >
> >             return true;
> >
> >         }

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