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Postings from December 2021
On Thu, Dec 09, 2021 at 01:41:29PM -0500, Felipe Gasper wrote:
>
> > On Dec 9, 2021, at 13:37, Dave Mitchell <davem@iabyn.com> wrote:
> >
> > On Thu, Dec 09, 2021 at 05:36:06PM +0000, Paul "LeoNerd" Evans wrote:
> >> This was the problem though - I couldn't work out how to keep @DB::args
> >> working in that situation.
> >
> > A more radical proposition would be to declare that @DB::args will always
> > return empty for signature subs.
>
> Would that break stack traces--or at least the argument-listing part of
> them?
Yes.
> If so, that would seem to be an unfortunate disincentive to adopt signatures.
Here's the current disclaimer in caller()'s pod:
Be aware that setting C<@DB::args> is I<best effort>, intended for
debugging or generating backtraces, and should not be relied upon. In
particular, as L<C<@_>|perlvar/@_> contains aliases to the caller's
arguments, Perl does not take a copy of L<C<@_>|perlvar/@_>, so
C<@DB::args> will contain modifications the subroutine makes to
L<C<@_>|perlvar/@_> or its contents, not the original values at call
time. C<@DB::args>, like L<C<@_>|perlvar/@_>, does not hold explicit
references to its elements, so under certain cases its elements may have
become freed and reallocated for other variables or temporary values.
Finally, a side effect of the current implementation is that the effects
of C<shift @_> can I<normally> be undone (but not C<pop @_> or other
splicing, I<and> not if a reference to L<C<@_>|perlvar/@_> has been
taken, I<and> subject to the caveat about reallocated elements), so
C<@DB::args> is actually a hybrid of the current state and initial state
of L<C<@_>|perlvar/@_>. Buyer beware.
@DB::args should never have been added. This gives us a chance to remove it
without breaking backwards compatibility.
--
A major Starfleet emergency breaks out near the Enterprise, but
fortunately some other ships in the area are able to deal with it to
everyone's satisfaction.
-- Things That Never Happen in "Star Trek" #13
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