The XS part of AlarmZone::new(SV* security_credentials, int zone) increases the reference count of security_credentials with SvREFCNT_inc() or similar, retains a pointer to the SV*, and decreases the reference count in AlarmZone->DESTROY(). This is the cleanest idea I can think of (reference counting stays in the Perl area of the program, C++ part continues unaware of Perl's existence.). I am stuck working out the details though, in particular where to store the security_credentials pointer (so it can be used later in DESTROY()).

You have to add magic to the inner blessed SV with sv_magicext, here is an example.

/* declare as 5 member, not normal 8 to save image space*/
const static struct {
    int (*svt_get)(SV* sv, MAGIC* mg);
    int (*svt_set)(SV* sv, MAGIC* mg);
    U32 (*svt_len)(SV* sv, MAGIC* mg);
    int (*svt_clear)(SV* sv, MAGIC* mg);
    int (*svt_free)(SV* sv, MAGIC* mg);
} my_vtbl = {
    NULL, NULL, NULL, NULL, NULL
};

/* puts newsv, refcnt++ed (caller doesn't have to do it), in sv as hid
+den magic SV */
STATIC void setMgSV(pTHX_ SV * sv, SV * newsv) {
    MAGIC * mg;
    if(SvRMAGICAL(sv)) { /* implies SvTYPE  >= SVt_PVMG */
        mg = mg_findext(sv, PERL_MAGIC_ext, &my_vtbl);
        if(mg) {
            SV * oldsv;
            SvREFCNT_inc_simple_void_NN(newsv);
            oldsv = mg->mg_obj;
            mg->mg_obj = newsv;
            SvREFCNT_dec(oldsv);
        } else {
            goto addmg;
        }
    }
    else {
        addmg:
        sv_magicext(sv,newsv,PERL_MAGIC_ext,&my_vtbl,NULL,0);
    }
}



# xsub to attach a hidden SV in RV inside to the target SV of RV outsi
+de
# both params must be references
# void SetMagicSV(outside, inside)
void
SetMagicSV(...)
PREINIT:
    SV * outside;
    SV * inside;
CODE:
    if(items != 2)
        croak_xs_usage(cv, "outside, inside");
    inside = POPs;
    outside = POPs;
    PUTBACK;
    if(SvROK(outside) && SvROK(inside)) {
        outside = SvRV(outside);
        inside = SvRV(inside);
    }
    else{
        croak_xs_usage(cv, "outside, inside");
    }
    setMgSV(aTHX_ outside, inside);
    return;
[download]

The other ideas is to have the inner SV be an AV or HV instead of an SVIV as is typically for XSPP wrapped C++ objs.

Another idea is link the 2 perl objs that mirror C++ objs in pure perl in a public API pure perl obj that has refs to the 2 XS objs to make sure 1 of the XS objs doesn't go out of scope. I've seen in Perl's TAP/Test modules AUTOLOAD accessors that forward the outer obj's meth call to the inner obj's method from an AUTOLOAD-ed outer obj's method that doesn't exist in code, since you can't @ISA the inner obj class into the outer obj since the 2 objs are differently layed out internally (the outer is an hash, the inner a SVIV C++ obj). Someone else can describe more about that idea.