うに3つの<code>Fn</code>トレイトでコード化されています:</p>
<!--
* `FnOnce` consumes the variables it captures from its enclosing scope, known
as the closure’s *environment*. To consume the captured variables, the
closure must take ownership of these variables and move them into the closure
when it is defined. The `Once` part of the name represents the fact that the
closure can’t take ownership of the same variables more than once, so it can
only be called one time.
* `FnMut` can chan