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Fwd: New release ?
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From:
Brandon Black
Date:
January 5, 2007 15:52
Subject:
Fwd: New release ?
Message ID:
84621a60701051552w501f91eeh8c16dde91b7ed0e8@mail.gmail.com
[oops, resend to list]
On 1/5/07, Rafael Garcia-Suarez <rgarciasuarez@gmail.com> wrote:
> On 06/01/07, Brandon Black <blblack@gmail.com> wrote:
> > However, ->isa checks for those superclasses fail. Attached is a
> > short perl script that demonstrates what I'm talking about, which
> > seems rather inconsistent. Is this inconsistency something we want to
> > preserve for historical reasons, or should it be remedied (I could do
> > that either as a separate patch or as part of the c3 patch since it
> > touches on this code anyways).
>
> I don't know -- I suspect some code might rely on this too. The usual
> suspect would be in the UNIVERSAL:: namespace on CPAN. Also, since the
> superclasses of UNIVERSAL will also be subclasses of UNIVERSAL too,
> won't this be a risk of infinite recursion ?
>
It doesn't cause infinite recursion in method lookup, and the same
basic strategy can be used for isa lookup. The method lookup strategy
boils down to "recurse through @ISA looking for the method, then if
that fails, look at UNIVERSAL and recurse into its @ISA". The jump to
UNIVERSAL happens once explicitly, and then never again.
One can currently exploit this and make an infinite loop by putting
UNIVERSAL into the @ISA of a class in @UNIVERSAL::ISA, but then the
normal infinite loop catcher (the one that deals with normal classes
being their own parents) kicks in after 100 levels of recursion and
croaks.
I can't imagine what code on CPAN would rely on the
->isa('SUPERCLASS_OF_UNIVERSAL') check failing (then again, apparently
nobody expected it to succeed either or someone would have mentioned
this before).
-- Brandon
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