SAX: Next Round

[david at megginson.com]

John Cowan writes:

 > David Megginson scripsit:
 > 
 > > I'd like to lose EntityResolver and DTDHandler (who uses them?),
 > > but I don't know if we can.
 > 
 > Nope, nope, nope.  In particular, I still have a project to finish
 > a standard EntityResolver that understands Socats.  By having such
 > a thing, you can fit Socat support into arbitrary applications
 > using arbitrary SAX parsers.  Keep it.  As for DTDHandler, it
 > exposes stuff that XML 1.0 requires a parser to expose.

Yes, yes, yes, I know -- I've made the same argument before in many
places.  

In retrospect, I think that unparsed entities and notations were a
mistake for XML (there are less opaque and more web-friendly ways to
accomplish the same thing), but they're there in the REC and, as you
say, the spec is quite explicit about reporting requirements.  I was
just fantasising out loud...

 > > 1. Filter Interface
 > 
 > I propose a fourth alternative: provide ParserFilter as a helper
 > class, and don't have a separate interface.  Parser filters are
 > just parsers that have a "parser(Parser)" constructor.

Yes, but what interface should the helper class implement?  Will have
have a hard-coded level-two parser interface that knows about
namespace and lexical handlers?  What if we add another standard
capability in the future?

The advantage of a separate interface is that it's easy to mix and
match; the disadvantage of a separate interface is also that it's easy 
to mix and match.

 > One particularly nice feature of this is that it is the pattern
 > used by Java {Input,Output}Streams and Readers/Writers: Chain of
 > Responsibility.

I agree -- chain of responsibility is a great benefit of the filter
approach, however we manage it.


All the best,


David

-- 
David Megginson                 david at megginson.com
           http://www.megginson.com/

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