void
_INSTANCE(ref,type)
    SV *ref;
    char *type;
PROTOTYPE: $$
CODE:
{
    STRLEN len;
    if( SvROK(ref) && type && ( ( len = strlen(type) ) > 0 ) )
    {
        if( SvMAGICAL(ref) )
            mg_get(ref);
        if( sv_isobject(ref) )
        {
            if( sv_derived_from(ref,type) )
            {
                ST(0) = ref;
                XSRETURN(1);
            }
            else
            {
                I32 isa_type = 0;
                int count;

                ENTER;
                SAVETMPS;
                PUSHMARK(SP);
                XPUSHs( sv_2mortal( newSVsv( ref ) ) );
                XPUSHs( sv_2mortal( newSVpv( type, len ) ) );
                PUTBACK;

                if( ( count = call_method("isa", G_SCALAR) ) )
                {
                    I32 oldax = ax;
                    SPAGAIN;
                    SP -= count;
                    ax = (SP - PL_stack_base) + 1;
                    isa_type = SvIV(ST(0));
                    ax = oldax;
                }

                PUTBACK;
                FREETMPS;
                LEAVE;

                if( isa_type )
                {
                    ST(0) = ref;
                    XSRETURN(1);
                }
            }
        }
    }
    XSRETURN_UNDEF;
}