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Even if we have to bless the referenCE, does the blessing actually bind package subs on the referenT?
I'm trying to make a ref-counted C++ class using an HV's refcnt. Thus when the HV's refcount drop to zero, it should also delete the binded C++ object. It seems I should create an SV reference for my HV, and bless that SV. However, what should I do if I don't want to have a SV reference? > Date: Wed, 26 Oct 2011 10:20:11 +0200 > From: kaffeetisch gmx de > To: gtk-perl-list gnome org > Subject: Re: generic refcounted object perl binding > > On 26.10.2011 07:49, YangXi wrote: > > Ano ther question about wrapper design, in function gperl_new_object() > > where an new wrapper is newly created: > > > > ...... > > obj = (SV *)g_object_get_qdata (object, wrapper_quark); > > > > if (!obj) { > > ...... > > // created a hash > > obj = (SV *)newHV () ; > > _gperl_attach_mg (obj, object); > > g_object_ref (object); > > > > // created a SV wrapper for the hash > > sv = newRV_noinc (obj); > > sv_bless (sv, stash); > > ...... > > } > > ...... > > > > Why don't bless the HV directly, but instead creating another SV > > wrapping the HV, and bless that SV instead? > > That is how references work at the perl C API level, but also kind of > how they work in Perl directly. A reference to something is a separate > SV (with its own refcount, etc.), just like in Perl, where you can take > multiple references to the same variable. And if you to put something > into some namespace, you have to bless the reference, not the referent. > > > Why use noinc to create the wrapper? Shouldn't the SV wrapper holding a > > reference for HV? > > This is a common pattern when constructing references: we use > newRV_noinc as opposed to newRV because 'obj' from above is a new HV and > we want 'sv' to take ownership of the initial refcount. Thus, when 'sv' > goes out of scope it would normally take 'obj' with it. In Glib::Object > this is a bit more complicated because we want 'obj' to survive so that > we can find it later and hand it out again. This is done by > incrementing its refcount in Glib::Object::DESTROY (which is called when > 'sv' goes out of scope). > > I wanted to link to some XS tutorial covering all this, but the examp le > at <http://perldoc.perl.org/perlxstut.html#EXAMPLE-6> actually uses a > different pattern to achieve the same thing: it mortalizes both the > referent and the reference, so when the xsub returns both end up having > refcount=1 as well. (The sv_2mortal call for the reference is hidden in > the 'SV*' typemap.) > _______________________________________________ > gtk-perl-list mailing list > gtk-perl-list gnome org > http://mail.gnome.org/mailman/listinfo/gtk-perl-list |