p5pRT
commented
23 years ago From @andk
> The attached file shows that the code in base.pm is brain-dead. > This cripples Tk::JPEG
Michael\, please take note. The change was made in your patch 9576 without any explanation what you'd tried to accomplish. So I dig out your posting that for some reason is not on the p5p archive. Appended below.
-- andreas
From: Michael G Schwern \schwern@​pobox\.com Subject: [PATCH lib/base.pm t/lib/base.t] Fix subtle $VERSION mistakes with base.pm To: perl5-porters@perl.org Date: Thu\, 5 Apr 2001 21:53:21 +0100
Finally tracked down a very\, very\, very subtle bug in Class::Fields's base.pm that drove me bonkers today. It goes like this...
On older perls \< 5.6\, Exporter has no $VERSION defined.
If something is used via base.pm that doesn't have a $VERSION\, it will set $VERSION = '-1\, set by base.pm'. It does this so it knows not to try to require it again (think about use base qw(Tie::StdArray)).
Eariler versions of base.pm had a very subtle bug where instead of actually setting $VERSION it would instead do something nasty to that bit of the symbol table.
Consider the following...
package Foo; use base qw(Exporter); use IO::Socket;
IO::Socket then does this...
use Socket 1.3;
Socket.pm does this...
require Exporter; @ISA = qw(Exporter);
What happens when you require a specific version number? Perl calls Socket->VERSION. Normally this falls back to UNIVERSAL::VERSION\, but wait... *Exporter::VERSION has been mucked up\, perl thinks there's a method defined there. It calls it and it returns undef (with lots of screaming. In fact\, 5.004 just segfaults). Suddenly\, perl thinks Socket is of a version \< 1.3 and dies horribly.
Anyhow\, that bug was fixed in 3302 I think but never tested. This patch adds a test for that.
There's another *even more subtle* bug here. Consider...
package Foo; sub VERSION { 42 }
package Bar; use base qw(Foo);
Does base.pm set $Foo::VERSION? Nope. Why? Because the check just goes and sees if there's a VERSION entry in the symbol table but never actually checks if there's a scalar. This fixes that.
---end of forwarded message---
Migrated from rt.perl.org#6943 (status was 'resolved')
Searchable as RT6943$