W3C home > Mailing lists > Public > www-dom@w3.org > July to September 1998

Re: latest DOM spec 19980720

From: Stephen R. Savitzky <steve@crc.ricoh.com>
Date: 21 Jul 1998 10:34:04 -0700
To: Ted Bashor <bashor@crossroute.com>
Cc: www-dom@w3.org
Message-ID: <qcvhorglbn.fsf@gelion.crc.ricoh.com>
Ted Bashor <bashor@crossroute.com> writes:

> Stephen R. Savitzky wrote:
> >
> > o There is no type-safe way to convert a Node to any of its major
> >   subclasses.  The newly-added nodeName, nodeValue, and attributes
> >   attributes help a great deal, but it would be good to have conversion
> >   methods as well.  We have, e.g., "asElement", which returns the node if it
> >   is an Element, null otherwise.  This is _much_ more efficient than
> >   casting, which involves run-time type checking in Java.
> I would think that this API would be an extension useful in an
> implementation that optimized specifically for Java runtime speed. 
> However I'm guessing that the average consumer of the DOM is probably
> going to be happy enough with their language's default type checking
> mechanism.

Some languages don't _have_ a type-checking mechanism -- C++ is an example.
Also, the construct in question allows the user to skip the extra step of
checking the nodeType in many cases, so it's a speedup in _any_ language.

> The only reason I object to having it in the core spec is that from an
> OO point of view it is kind of ugly to have base classes A) know about
> all or even any of their subclasses B) have to be modified when a new
> subclass comes along.

I agree that it's ugly, and I wouldn't have suggested it except that the set
of core node type interfaces is small and fixed (or, rather, it would be
fixed if there were a Declaration subclass), and that the Document interface
already has a corresponding set of "create" operations.  The latter is the
most telling -- the DOM has already started down that path; one might as
well do it right.

Unfortunately, none of the common strongly-typed languages have constructs
that allow one to do this kind of thing correctly.  

 Stephen R. Savitzky   Chief Software Scientist, Ricoh Silicon Valley, Inc., 
<steve@rsv.ricoh.com>                            California Research Center
 voice: 650.496.5710   fax: 650.854.8740    URL: http://rsv.ricoh.com/~steve/
  home: <steve@starport.com> URL: http://www.starport.com/people/steve/
Received on Tuesday, 21 July 1998 13:29:36 UTC

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