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Re: [perl.git] branch doy/runtime_isa_manipulation_bug, created.v5.17.1-337-gbd8c24f
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From:
Jesse Luehrs
Date:
July 29, 2012 13:13
Subject:
Re: [perl.git] branch doy/runtime_isa_manipulation_bug, created.v5.17.1-337-gbd8c24f
Message ID:
20120729201252.GV30375@tozt.net
On Sun, Jul 29, 2012 at 12:49:07PM -0700, Father Chrysostomos wrote:
>
> On Jul 12, 2012, at 10:13 PM, Jesse Luehrs wrote:
>
> > On Thu, Jul 12, 2012 at 10:00:08PM -0700, Father Chrysostomos wrote:
> >>
> >> On Jul 10, 2012, at 5:50 PM, Jesse Luehrs wrote:
> >>> So the pure perl version worked fine, but I'm trying to adjust the XS
> >>> version to do the same thing, and I'm really not sure what the right way
> >>> to go about it is. gv_init isn't sufficient, because it doesn't attach
> >>> the appropriate magic. The only function that knows about the kinds of
> >>> magic that need to be attached to globs is gv_fetchpvn_flags, and that
> >>> requires a stash name, rather than a stash pointer. Is there any actual
> >>> API for stash aliasing in C (to work around this for now), or am I going
> >>> to need to poke around at the internals to emulate the behavior?
> >>
> >> In 5.10 you have to emulate it:
> >>
> >> sv_magic((SV *)GvAVn(gv), (SV *)gv, PERL_MAGIC_isa, NULL, 0);
> >>
> >> In 5.12 (d851b122) you can do this:
> >>
> >> SV *rv = newRV_noinc(newAV());
> >> sv_setsv(gv, rv);
> >> SvREFCNT_dec(rv);
> >>
> >> In 5.17.2 (986d39eeb4) you can do this:
> >>
> >> GvAVn(gv);
> >
> > Sure, but @ISA is only a single case of magical variables. What if gv
> > is intended for $main::{'^W'}, or something like that? I really don't
> > want to have to hardcode all of the different variables that might have
> > magic, especially since it changes between perl versions. The more I
> > look into it though, the more I can't really see it being reasonably
> > possible without modifications to the core (in particular, a variant of
> > gv_fetchpvn_flags that looks things up in a provided stash pointer,
> > rather than by name). I may have to just stick to name lookups in my
> > code until something like this makes its way into core.
>
> perlsub says this:
>
> The construct
>
> local *name;
>
> creates a whole new symbol table entry for the glob C<name> in the
> current package. That means that all variables in its glob slot ($name,
> @name, %name, &name, and the C<name> filehandle) are dynamically reset.
>
> This implies, among other things, that any magic eventually carried by
> those variables is locally lost. In other words, saying C<local */>
> will not have any effect on the internal value of the input record
> separator.
>
> I have always understood that to mean that undef */ stops $/ from working and it’s your own fault if you do that. (@ISA is different, in that its magicalness is not generally known, and 5.8 and earlier would reset all caches any time a subroutine was defined, preventing most of the stale cache problems we’ve had since 5.10.)
>
> Should that change? Maybe. I don’t know.
>
> Should we add a gv_add_magic API function? Maybe. I don’t know.
>
> What exactly is your use case?
This is all for Package::Stash - I'm trying to get it to work properly
with anonymous stashes (Package::Anon for now, although the long term
goal is to have actual anonymous stash support in core). This means that
I need to be able to apply things like @ISA magic when manipulating @ISA
even if there is no name attached to the stash, which is difficult
because gv_fetchpvn_flags is the only API to any of this, and its API
requires the name of a package variable.
I can work around this by bypassing gv_fetchpvn_flags (just doing a hash
lookup on the stash HV* and using gv_init when necessary) and applying
@ISA magic manually when necessary, but then I need to do things like be
sure to also apply magic for $OVERLOAD (but only for certain versions of
perl), and then things like $] also break, because the logic for
autovivifying those variables is also in gv_fetchpvn_flags.
The issue is that gv_fetchpvn_flags does about four different things -
converting fully qualified package variable names to a stash and key
(including forcing things into main when necessary), looking up the
actual variable in the stash that it found, calling gv_init to make sure
there is a glob in the stash slot, and then applying whatever magic is
appropriate to that variable before returning it. Splitting this up
into a couple smaller functions that could be reused separately would
make things a lot easier to work with - if I have an actual stash, I
shouldn't have to convert it back into a name just so that I can pass it
to this function which then goes and converts it directly back into a
stash.
-doy
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