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where is sv_setrv?

by patcat88 (Deacon)
on Dec 16, 2011 at 20:58 UTC ( #944012=perlquestion: print w/ replies, xml ) Need Help??
patcat88 has asked for the wisdom of the Perl Monks concerning the following question:

Simple question, where is sv_setrv? AFAIK it doesn't exist. Why? So how in XS, do you take an existing SV, and make it be a reference to another SV? sv_setsv(existingSV, sv_2mortal(newRV_inc(targetSV)))? there has to be a less bloated way that uses SvRV_set somehow.

Comment on where is sv_setrv?
Re: where is sv_setrv?
by ikegami (Pope) on Dec 16, 2011 at 23:59 UTC

    According to newSVrv, it's

    SV_CHECK_THINKFIRST_COW_DROP(rv); (void)SvAMAGIC_off(rv); if (SvTYPE(rv) >= SVt_PVMG) { const U32 refcnt = SvREFCNT(rv); SvREFCNT(rv) = 0; sv_clear(rv); SvFLAGS(rv) = 0; SvREFCNT(rv) = refcnt; sv_upgrade(rv, SVt_IV); } else if (SvROK(rv)) { SvREFCNT_dec(SvRV(rv)); } else if (SvTYPE(rv) < SVt_PV && SvTYPE(rv) != SVt_IV) { sv_upgrade(rv, SVt_IV); } else if (SvTYPE(rv) >= SVt_PV) { SvPV_free(rv); SvLEN_set(rv, 0); SvCUR_set(rv, 0); } SvOK_off(rv); SvRV_set(rv, sv); SvROK_on(rv); SvREFCNT_inc(sv); SvSETMAGIC(rv);

    Or you could use

    sv_replace(rv, newRV_inc(sv)) SvSETMAGIC(rv);

    Update: Fixed ref count as per reply.

      Your version of newSVrv wouldn't work. Its only 5.12 compatible, not before, because of the SV type changes and the prepare_SV_for_RV macro changed. Can RVs have a PV string pointer (flags off of course)? Does an RV always have to be of type SVt_RV (5.10) or SVt_IV (5.12) or any SV with ROK can be a reference? The sv_replace seems like the safest idea while i'm writing this.

      There is a missing refcount inc on sv before "SvRV_set(rv, sv);". Also there is a macro for the old RV sv type to IV, seems to me that it will provide backwards compatibility sv.h#l75 in perl.git

        Your version of newSVrv wouldn't work [before Perl 5.12]

        It's not a version of newSVrv, and you're free to do the exercise yourself for 5.10.

        Can RVs have a PV string pointer

        Like you just said, there's no such thing as an RV anymore.

        Does an RV always have to be of type SVt_IV (5.12) or any SV with ROK can be a reference?

        Latter. Even before 5.12.

        The sv_replace seems like the safest idea while i'm writing this.

        That's quite an understatement.

        There is a missing refcount inc on sv before "SvRV_set(rv, sv);".

        You're saying that newSVrv causes referenced material to be destroyed permaturely. I don't believe you.

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