eaf</code>が今では<code>Rc&lt;Node&gt;</code>への唯一の参照に再度なったからです。</p>
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All of the logic that manages the counts and value dropping is built into
`Rc<T>` and `Weak<T>` and their implementations of the `Drop` trait. By
specifying that the relationship from a child to its parent should be a
`Weak<T>` reference in the definition of `Node`, you’re able to have parent
nodes point to child nodes and vice versa without creating a reference cycle
and memory leaks.
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