AUTOLOADED pre- and post- handler methods?

[Dan Sugalski]

Here's a question for the python/ruby folks.

I know (now) that python lets you have an interceptor method that
gets called before a named method is called even. Does it allow this
method to be generated by the generic fallback method?

In Perl terms, assume we have a method PRE that gets called before
any method in a class is called, and AUTOLOAD which is called if you
call a method on a class and that method doesn't exist. Does AUTOLOAD
have to get called to check for PRE if PRE doesn't exist in a class?
--
Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski even samurai
d...@sidhe.org have teddy bears and even
teddy bears get drunk

[Christopher Armstrong]

Dan Sugalski <d...@sidhe.org> writes:
> I know (now) that python lets you have an interceptor method that gets
> called before a named method is called even. Does it allow this method
> to be generated by the generic fallback method?

Python doesn't really have "interceptor methods". In fact, there
aren't any magic methods that are called specifically on method
calling -- only attribute access (well, except for __call__, which
happens when you do obj(), but that's a separate step in the process).

__getattribute__(self, name) --> Always called on attribute access.

__getattr__(self, name) --> Called after looking up the attribute
fails by regular means.

__get__(self, obj, type=None) --> Called on an object when that object
is accessed as an attribute of
another object. f34r this. :-)

Any of which, of course, can return methods. :-) btw, remember how
Python creates `bound methods' when you access a method through an
instance? It's implemented with (the C equivalent of) __get__ (As of
Python 2.2). More information related to that (and other useful
information in general) is here:
http://www.python.org/2.2.2/descrintro.html.

Btw, these all have `set' and `del' friends, but they don't always
perfectly match up with the `get's... I'll get back to you on that.

--
Twisted | Christopher Armstrong: International Man of Twistery
Radix | Release Manager, Twisted Project
---------+ http://twistedmatrix.com/users/radix.twistd/

[Rafael Garcia-Suarez]

Dan Sugalski wrote in perl.perl6.internals :

>
> In Perl terms, assume we have a method PRE that gets called before
> any method in a class is called, and AUTOLOAD which is called if you
> call a method on a class and that method doesn't exist. Does AUTOLOAD
> have to get called to check for PRE if PRE doesn't exist in a class?

In Perl 5, AUTOLOAD is called for destructors :

$ perl -wle 'sub AUTOLOAD{print $AUTOLOAD};bless{}'
main::DESTROY

While I think this is annoying in most cases, I imagine this may be
useful. And adding an empty destructor to a class is not a huge effort.

The situation is similar for a PRE method. If it's not defined, there's
no error ; if it's not defined but if AUTOLOAD exists, AUTOLOADing is
tried. (I imagine that if AUTOLOAD gracefully refuses to create the PRE
method, no further attempt will be made.)