Re: Reserve_Capacity for Unbounded_String?

["Randy Brukardt" <randy@rrsoftware.com>]

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"Pascal Obry" <pascal@obry.net> wrote in message
news:46A69136.3010803@obry.net...
> Randy Brukardt a �crit :
> > Maybe some uninformed users, but not anyone who doesn't add non-existent
> > requirements to the specs.
> >
> > Unbounded_String is best used for storage (not calculation) of values.
It is
> > a horrible design for calculation, no matter what schemes you use for
the
> > implementation.
> >
> > Moreover, I've yet to see an example where the performance of
> > Unbounded_Strings (allocation-wise) matters. Our spam filter was written
> > solely using Unbounded_Strings, it does a lot of calculation
(normalization
> > of e-mail) and still the allocation overhead is insignificant. (The
> > bottleneck is in Index, which does no allocation at all.)
> >
> > I can imagine that it would be possible to write a program where the
> > allocation overhead would matter, but such a program would be helped a
lot
> > more by avoiding Unbounded_Strings (and *all* of their allocation
overhead)
> > than by tweaking the implementation of Unbounded_Strings to reduce that
> > overhead in a few rarely used operations.
> >
> > So I stand by my original statement. Anyone that depends on the
performance
> > characteristics of a particular implementation (of anything!) is an
idiot
> > and will be burned in the future.
>
> Well Randy, its all too easy to dismiss points like this by saying that
> you have not seen a problem with the current implementation and if
> somebody show you something wrong in this area then he has to use
> something else that Unbounded_String... At least that's the way I'm
> reading your message.
>
> Just try this on your implementation:
>
>    C : constant Character := 'x';
>
>    U : Unbounded_String;
>
>    for k in 1 .. 5_000_000 loop
>       U := U & C;
>    end loop;
>
> And then test it with GNAT. Of course that is not a real example but
> very close to something done in my templates engine.
>
> You were speaking about performance about checking the preallocated
> buffer. My point is that it is not that costly compared to the price of
> reallocating a whole string thousands of time.
>
> Pascal.
>
> -- 
>
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> --| Pascal Obry                           Team-Ada Member
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