[Dahut-pm] QNames and Loaded Magic

[Michael Nachbaur]

I've read the chat log and your code blow.  I think this would totally 
rock for RDF munging work, especially given the darobin/ubu idea of 
lazily following resource URIs to get nested data.

So, very neat.  I want! :-)  I think the ^ is an acceptable work-around 
for ":" being reserved.

If anyone needs help with this (ubu?) I'd be glad to pitch in.  I'm 
doing a lot of RDF work in both Perl and Mozilla/XPCOM these days, so 
this is very much on my mind.

On Apr 20, 2005, at 5:01 AM, Robin Berjon wrote:

> DAHUT!
>
> While chatting with ubu it turned out that there would be interest in 
> being able to call $obj->foo:bar(...) where foo:bar is a method that 
> corresponds to a QName (for XML, RDF, etc.). Unfortunately, ':' is 
> reserved there and can't be used. But other characters, which are 
> illegal in NCNames, can be used there with a little trickery.
>
> In this case I picked '^'. It could be '|' or a host of others. The 
> former seemed less intrusive, the latter has stronger 'or' 
> connotations but has the advantage of being the namespace separator 
> used by CSS.
>
> The code uses a bit of AUTOLOAD and overload. Tell me what you think, 
> is that a nice way of hacking qnames into Perl? The code is a bit long 
> but almost all of it is meant to be hidden.
>
>
> # this is the main package
> # we use an AUTOLOAD directly but it could have been installed by
> # a module being use'd (which could look to see if there is already
> # one and give up).
> # The idea is that one can call $obj->foo^bar() where foo^bar 
> represents
> # the foo:bar QName (mapping to IRIs is left as an exercize to the 
> reader)
> # Downsides are that an AUTOLOAD cannot exist, and that the QName must 
> have
> # a () even if it doesn't have arguments.
>
> use strict;
> use vars qw/$AUTOLOAD/;
>
> my $obj = Object->new;
> $obj->foo^bar('dahut', 'Bender');
>
> sub AUTOLOAD {
>     my @args = @_;
>     my $ln = ($AUTOLOAD =~ /([^:]+)$/)[0];
>     return if $ln eq 'DESTROY';
>     print "AUTOLOAD main: $ln\n";
>     return LocalName->new( name => $ln, args => \@args );
> }
>
> # any method on foo, being incomplete (the part before the ^)
> # returns a Prefix object. Nothing special.
>
> package Object;
> use vars qw/$AUTOLOAD/;
> sub new { return bless []; }
> sub AUTOLOAD {
>     my $self = shift;
>     my $pfx = ($AUTOLOAD =~ /([^:]+)$/)[0];
>     return if $pfx eq 'DESTROY';
>     print "AUTOLOAD: $pfx\n";
>     return Prefix->new( prefix => $pfx, object => $self );
> }
>
> # LocalName objects deal with the rhs of the ^. They save the
> # local name and the arguments so that they can be accessed later.
>
> package LocalName;
> sub new {
>     shift;
>     my %opts = @_;
>     return bless \%opts;
> }
>
> # Prefix is the lhs of the ^, and it knows both which prefix was
> # used and which object it was called on.
> # It uses overloading so that the bitwise ^ operator calls
> # makeMeth. What the latter does is up to you. This one
> # dumps the info to show what you get, which should be enough to
> # call a method of your own.
>
> package Prefix;
> use overload '^' => \&makeMeth;
> use Data::Dumper;
> sub new {
>     shift;
>     my %opts = @_;
>     return bless \%opts;
> }
>
> sub makeMeth {
>     my $pfx = shift;
>     my $ln = shift;
>     # you figure out what to do here
>     print Dumper({ pfx_context => $pfx, ln_params => $ln });
> }
>
>
>
>
>
> -- 
> Robin Berjon
>   Research Scientist
>   Expway, http://expway.com/
>
>
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--
Michael Nachbaur <mike at nachbaur.com>
http://nachbaur.com/pgpkey.asc