What if you forget to use that and just use let or const? It is better than plain try-finally or defer because you don't have to remember how to dispose of the resources but in terms of remember to dispose of the resource at all, I don't think that is all that different from Python's with or Java's try-with-resources. You can just forget to use using, with, try-with-resources.

There isn't any way to forget to drop a resource if you have RAII.