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.
Your opinions, please...? :)
- Sebastian