/* 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 hidden 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 outside
# 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;