mirror of
https://github.com/rust-unofficial/patterns
synced 2024-11-18 15:25:37 +00:00
47 lines
2.0 KiB
Markdown
47 lines
2.0 KiB
Markdown
# Iterating over an `Option`
|
|
|
|
## Description
|
|
|
|
`Option` can be viewed as a container that contains either zero or one elements. In particular, it implements the `IntoIterator` trait, and as such can be used with generic code that needs such a type.
|
|
|
|
## Examples
|
|
|
|
Since `Option` implements `IntoIterator`, it can be used as an argument to [`.extend()`](https://doc.rust-lang.org/std/iter/trait.Extend.html#tymethod.extend):
|
|
|
|
```rust
|
|
let turing = Some("Turing");
|
|
let mut logicians = vec!["Curry", "Kleene", "Markov"];
|
|
|
|
logicians.extend(turing);
|
|
|
|
// equivalent to
|
|
if let Some(turing_inner) = turing {
|
|
bar.push(turing_inner);
|
|
}
|
|
```
|
|
|
|
If you need to tack an `Option` to the end of an existing iterator, you can pass it to [`.chain()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.chain):
|
|
|
|
```rust
|
|
let turing = Some("Turing");
|
|
let logicians = vec!["Curry", "Kleene", "Markov"];
|
|
|
|
for logician in logicians.iter().chain(turing.iter()) {
|
|
println!("{} is a logician", logician);
|
|
}
|
|
```
|
|
|
|
Note that if the `Option` is always `Some`, then it is more idiomatic to use [`std::iter::once`](https://doc.rust-lang.org/std/iter/fn.once.html) on the element instead.
|
|
|
|
Also, since `Option` implements `IntoIterator`, it's possible to iterate over it using a `for` loop. This is equivalent to matching it with `if let Some(..)`, and in most cases you should prefer the latter.
|
|
|
|
## See also
|
|
|
|
* [`std::iter::once`](https://doc.rust-lang.org/std/iter/fn.once.html) is an iterator which yields exactly one element. It's a more readable alternative to `Some(foo).into_iter()`.
|
|
|
|
* [`Iterator::filter_map`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter_map) is a version of [`Iterator::flat_map`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flat_map), specialized to mapping functions which return `Option`.
|
|
|
|
* The [`ref_slice`](https://crates.io/crates/ref_slice) crate provides functions for converting an `Option` to a zero- or one-element slice.
|
|
|
|
* [Documentation for `Option<T>`](https://doc.rust-lang.org/std/option/enum.Option.html)
|