Need to setup singleton_class chain; fix
MODIFY
src/class.c
src/class.c
@@ -97,6 +97,7 @@ prepare_singleton_class(mrb_state *mrb, struct RBasic *o)
}
else {
sc->super = o->c;
+ prepare_singleton_class(mrb, (struct RBasic*)sc);
}
o->c = sc;
mrb_field_write_barrier(mrb, (struct RBasic*)o, (struct RBasic*)sc);

Need to setup singleton_class chain; fix #3509