eval.c:233
static void
rb_clear_cache_for_undef(klass, id)
    VALUE klass;
    ID id;
{
    struct cache_entry *ent, *end;

    if (!ruby_running) return;
    ent = cache; end = ent + CACHE_SIZE;
    while (ent < end) {
	if (ent->origin == klass && ent->mid == id) {
	    ent->mid = 0;
	}
	ent++;
    }
}
