rb_ivar_lookup   1335 error.c            recv = rb_ivar_lookup(self, id_receiver, Qundef);
rb_ivar_lookup   1446 internal.h     VALUE rb_ivar_lookup(VALUE obj, ID id, VALUE undef);
rb_ivar_lookup   1259 variable.c         VALUE iv = rb_ivar_lookup(obj, id, Qundef);
rb_ivar_lookup   1272 variable.c         return rb_ivar_lookup(obj, id, Qnil);