develooper Front page | perl.perl6.language | Postings from June 2005

Re: AUTLOAD and $_

Thread Previous | Thread Next
June 20, 2005 16:23
Re: AUTLOAD and $_
Message ID:
chromatic skribis 2005-06-20 15:58 (-0700):
> I think:
> 	sub AUTOLOAD {}
> is better than:
> 	sub AUTOLOAD { return sub {} }

It's nicer to type, but I think that your preferred syntax means that
the AUTOLOAD sub itself has to call any loaded code, which can mean that it
has to fit arbitrary given arguments to an arbitrary signature, which I
think is way too hard.

One alternative, that I don't like, is to ignore non-subref returns, but
call a returned subref. Then something else has to indicate failure, and
that thing is probably fail. The problem that I have with that is that
you lose the free verbose, clear and standard error message you could
otherwise have. Unless fail here uses a default that isn't $_ or $!, and
I do not like special cases like that.

Note that as long as empty closures can be typed without the sub
keyword, and the return keyword is optional for the last statement, the
following is perhaps a syntactically more satisfying solution for you:

    sub AUTOLOAD {{}}

If I understand things correctly, a null closure will have such small
overhead that you can pass it around just as freely as integers. Of
course, calling the empty closure can be optimized away, although I hope
I also understand correctly that the overhead of calling something is
also so drastically reduced since Perl 5, that {}() is not much heavier
than do {} or the null statement between two semicolons: ;;.

> Or have I misunderstood the proposal and the purpose of AUTOLOAD?

Well, the purpose I think you have misunderstood, as your example
doesn't LOAD anything. But then, I have always thought AUTOLOAD was a
bad name, because it is so much more powerful than that. Perhaps
DEFAULT, FALLBACK or MISSINGSUB would be more appropriate.

I also don't see the symmetry between AUTOLOAD and AUTOMETH. Two things
bother be about that: LOAD versus METH, while it should be SUB versus
METH, and that METHOD is abbreviated while in the method keyword it is
not. Either it should be abbreviated everywhere: meth foo { ... }, or
nowhere: AUTOMETHOD. I personally like the "meth foo { ... }".


Thread Previous | Thread Next Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at | Group listing | About