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   Re: [xml-dev] The subsetting has begun

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> Karl Waclawek scripsit:
> > Maybe that is different for Java, but in general this is simply wrong.
> If you mean "in C++", say so, not "in general". 

No, I do mean: to say that using exceptions for common program flow
control is what they are meant for, is not true in general.

> The IBM implementation
> of Cobol made procedure calls very expensive, and most Cobol programmers
> never wrote a subroutine throughout their careers, and only invoked them
> for the sake of DBMS access, where they had no choice.  That didn't make
> procedure calls in general a bad idea.
> > Apart from that they are expensive in most languages.
> Expensive compared to what?  If every procedure must return status, and
> every caller must check the status and decide whether to itself return
> status or carry on, your code size enlarges immensely and so does your
> execution time.

Not compared to exceptions. Memory allocation and deallocation
is very expensive across most languages. You can alleviate this somewhat
with a smart garbage collector, but only to a degree.

And also, checking numbers is extremely fast on today's CPUs.
The only thing to be concerned here would be call overhead.

>  The alternative is to do what most C programmers do,
> ignore status returns and carry on.  We all know where that leads.

I think I said something about using status in low level code
and leave the decision about exceptions to high level code
with sufficient context to make it.

> > And you have to trap them in your app, since you might not actually want to
> > terminate the routine where the parse call returns to.
> We were discussing the use of exceptions precisely to terminate parsing.

Exactly, but then you want to continue parsing another 2000 files
in the same loop. We even added a Reset function to the Expat parser
(instead of Free and Re-Create) to cater to these kinds of use cases.
> > Well, we (a group of programmers) ported SAX2 to Delphi.
> > On Delphi the idea of using exceptions for regular program flow control
> > is just not right. Same in C++.
> You may be right: I don't know either C++ or Delphi particularly.  But I
> notice that Stroustrup took the trouble of making sure exceptions got into
> C++, which means that he must think they are good for something.

Yes, they do and I use them all the time. That is, for dealing with the
exceptional cases.
> > And like C++, Delphi is sometimes used for speed, meaning that
> > one takes care about memory allocations. Exceptions are too
> > expensive from that point of view, which matters if the program
> > is meant to continue, and matters less if the current context has to
> > be terminated.
> It is well known that claims of efficiency and inefficiency mean nothing
> unless backed up with numbers, for programmers' intuition on the subject
> is notoriously in error.

This is no intuition. I can whip up a quick demo in Delphi
(I already did - took 5 minutes) which shows that passing a Boolean result
up from a 5 levels deep nested procedure call executed in a loop is at least
100 times as fast as throwing and catching an exception for the same purpose.
I can post or e-mail it if you really want to see it.



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