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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: The subsetting has begun
 > 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. Karl 
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