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Ch. 13: `unwrap_or_else` takes all three kinds of closures

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Chris Krycho 2024-04-19 13:31:53 -06:00 committed by GitHub
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@ -329,13 +329,13 @@ Using `FnOnce` in the trait bound expresses the constraint that
`unwrap_or_else` is only going to call `f` at most one time. In the body of
`unwrap_or_else`, we can see that if the `Option` is `Some`, `f` won’t be
called. If the `Option` is `None`, `f` will be called once. Because all
closures implement `FnOnce`, `unwrap_or_else` accepts all closures and is as
flexible as it can be.
closures implement `FnOnce`, `unwrap_or_else` accepts all three kinds of
closures and is as flexible as it can be.
> Note: Functions can implement all three of the `Fn` traits too. If what we
> want to do doesn’t require capturing a value from the environment, we can use
> the name of a function rather than a closure where we need something that
> implements one of the `Fn` traits. For example, on an `Option<Vec<T>>` value
> implements one of the `Fn` traits. For example, on an `Option<Vec<T>>` value,
> we could call `unwrap_or_else(Vec::new)` to get a new, empty vector if the
> value is `None`.