src/flow_control/let_else.md

# let-else

> 🛈 stable since: rust 1.65
>
> 🛈 you can target specific edition by compiling like this
> `rustc --edition=2021 main.rs`

With `let`-`else`, a refutable pattern can match and bind variables
in the surrounding scope like a normal `let`, or else diverge (e.g. `break`,
`return`, `panic!`) when the pattern doesn't match.

```rust
use std::str::FromStr;

fn get_count_item(s: &str) -> (u64, &str) {
    let mut it = s.split(' ');
    let (Some(count_str), Some(item)) = (it.next(), it.next()) else {
        panic!("Can't segment count item pair: '{s}'");
    };
    let Ok(count) = u64::from_str(count_str) else {
        panic!("Can't parse integer: '{count_str}'");
    };
    (count, item)
}

fn main() {
    assert_eq!(get_count_item("3 chairs"), (3, "chairs"));
}
```

The scope of name bindings is the main thing that makes this different from
`match` or `if let`-`else` expressions. You could previously approximate these
patterns with an unfortunate bit of repetition and an outer `let`:

```rust
# use std::str::FromStr;
#
# fn get_count_item(s: &str) -> (u64, &str) {
#     let mut it = s.split(' ');
    let (count_str, item) = match (it.next(), it.next()) {
        (Some(count_str), Some(item)) => (count_str, item),
        _ => panic!("Can't segment count item pair: '{s}'"),
    };
    let count = if let Ok(count) = u64::from_str(count_str) {
        count
    } else {
        panic!("Can't parse integer: '{count_str}'");
    };
#     (count, item)
# }
#
# assert_eq!(get_count_item("3 chairs"), (3, "chairs"));
```

### See also:

[option][option], [match][match], [if let][if_let] and the [let-else RFC][let_else_rfc].

[match]: ./match.md
[if_let]: ./if_let.md
[let_else_rfc]: https://rust-lang.github.io/rfcs/3137-let-else.html
[option]: ../std/option.md