[fpc-devel]SAX poll

Michael Van Canneyt michael.vancanneyt at wisa.be
Thu Nov 23 17:12:58 CET 2000

On Thu, 23 Nov 2000, Sebastian [iso-8859-1] Günther wrote:

> Hello *,
> I need everybody's opinion on a new unit which will be available soon:
> SAX is the Simple API for XML. It defines an interface for XML parsers,
> which use callbacks to report events such as 'start tag processed',
> 'comment processed' and so on. There shouls be some parsers around which
> are compatible to SAX, but most of them are written in Java.
> In SAX, events are being reported by calling methods of a special
> interface. Applications register these interfaces at the parser at
> startup. Such an interface looks like this:
>   ISAXErrorHandler = interface
>     procedure Error(AException: ESAXParseException);
>     procedure FatalError(AException: ESAXParseException);
>     procedure Warning(AException: ESAXParseException);
>   end;
> I have a FPC version almost finished, but now, that the main branch
> compiler supports interfaces, some questions remain:
> 1. Implementation with interfaces or classes
> It would be possible to define _all_ SAX interfaces, including the ones
> for the parser, as interface in FPC. The other option would be to define
> only the callback interfaces as interface, everything else uses classes.
> Using interfaces everywhere would be more conformant to SAX, but the
> latter solution is faster. The first one only makes sense, if somebody
> plans to use a different SAX parser than the default one with FPC. (the
> parser itself won't be included in the SAX unit, it will be possible to
> use different parsers with the upcoming SAX unit anyway. But using the
> classes approach, all parsers must be written explicitly for this SAX
> unit.)
> 2. Using callback interfaces or method properties
> If the FPC SAX unit won't use interfaces everywhere, it must be
> considered to dump the callback interfaces as well: Java etc. need such
> callback interfaces, as they don't know the concept of 'method
> properties', i.e. properties or fields in classes which store a method
> pointer. But as FPC is more powerful than 'those other languages', we
> could use such properties instead. For example, for the ErrorHandler
> case, the XMLReader.SetErrorHandler and XMLReader.GetErrorHandler
> methods would be replaced by something like this:
>   TSAXXMLReader = class
>     ...
>     property OnError(AException: ESAXParseException) read ... write ...;
>     property OnFatalError(AException: ESAXParseException) read ... write
> ...;
>     property OnWarning(AException: ESAXParseException) read ... write
> ...;
>   end;
> I'm personally are in favour of the more ObjectPascal specific
> solutions, as they are faster and better to use within Pascal programs.

I also think this is what should be used. It will result in the
fastest performance, is conceptually much simpler and closer to
what Delphi programming is all about.


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