��する-rctをweaktに変換する">循環参照を回避する: <code>Rc&lt;T&gt;</code>を<code>Weak&lt;T&gt;</code>に変換する</a></h3>
<!--
So far, we’ve demonstrated that calling `Rc::clone` increases the
`strong_count` of an `Rc<T>` instance, and an `Rc<T>` instance is only cleaned
up if its `strong_count` is 0. You can also create a *weak reference* to the
value within an `Rc<T>` instance by calling `Rc::downgrade` and passing a
reference to the `Rc<T>`. When you call `Rc::downgrade`, you get 