Re: What would you like to see in XML::LibXML ?

On Mon, 2012-01-30 at 14:09 +0200, Shlomi Fish wrote:
> On Mon, 30 Jan 2012 11:38:44 +0000
> Tim Brody <[email protected]> wrote:
> 
> > On Sun, 2012-01-29 at 22:11 +0200, Shlomi Fish wrote:
> > > Hi Aaron,
> > > 
> > > On Sun, 29 Jan 2012 14:49:36 +0000
> > > Aaron Crane <[email protected]> wrote:
> > > 
> > > > Shlomi Fish <[email protected]> wrote:
> > 
> > > > I'd particularly value the ability to annotate a node with a Perl
> > > > scalar, and retrieve that scalar later — much like the per-node
> > > > `_private` data in libxml2, but accessible to Perl code.  Straw-man
> > > > API:
> > > > 
> > [snip]
> > > Yes, it would be very tricky. One option to overcome this may be to make these
> > > annotations be “tokens” which are arbitrary perl strings or numbers, but not
> > > arbitrary perl scalars. The XML-LibXML programmer will be able to map or
> > > unpack these tokens into something more complex, but it would be their
> > > responsibility to allocate unique tokens and to free their resources later.
> > > 
> > > We can potentially make these annotations be dictionaries mapping «strings =>
> > > strings» (using perl's built-in hashes, or balanced binary trees or whatever),
> > > but I guess we can stop there. 
> > > 
> > > I guess that would be the case of a leaky abstraction (see
> > > http://en.wikipedia.org/wiki/Leaky_abstraction , http://www.joelonsoftware.com/articles/LeakyAbstractions.html )
> > > or a quirky abstraction (see http://shlomif-tech.livejournal.com/49510.html ),
> > > but if it makes our life easier….
> > 
> > What if we overloaded the node stringification to return the memory
> > address of the libxml node instead of the Perl scalar?
> > 
> > use overload '"' =>
> > 	sub { sprintf("%s(0x%x)", ref($_[0]), $_[0]->_addr) };
> > 
> > Where _addr returns the pointer address of the *libxml* node (not
> > proxy).
> > 
> > Which, I think, would allow this to work:
> > $SLOW_STUFF{$node} = { ... };
> > 
> > This would need a big health warning about the difference between
> > ref($node) and "$node".
> > 
> 
> I don't like this approach too much. It raises many problems, and while being
> relatively easy to implement, I would prefer to give the user the option to
> annotate the node either with one datum or (preferably) with several named
> values (stored in a «string => string» hash). That will be, given sufficient
> support from libxml2 (like a freeing-callback), more flexible, powerful and
> safer.

What problems does it raise?

I'm unsure about adding (non-DOM) annotations to LibXML, when the more
robust approach for storing contextual data is using a hash of
object-references:

$INFO{$obj1} = "foo";
$INFO{$obj2} = "bar";

The trouble with LibXML is it breaks that Perlish approach.

All the best,
Tim.

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