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Fairer examples

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Jules Bertholet 2024-05-16 23:14:22 -04:00
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text/3627-match-ergonomics-2024.md
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@ -334,14 +334,14 @@ anyway is that the current behavior is unintuitive and surprising for users.
```rust
//! All editions: works only with this rule
let &[[a]] = &[&mut [42]]; // x: &i32
let &(i, j, [s]) = &(63, 42, &mut [String::from("🦀")]); // i: i32, j: i32, s: &String
```
```rust
//! All editions: works with or without this rule (alternative to above)
// Note the explicit `ref`, we must abandon match ergonomics
let &[[ref a]] = &[&mut [42]]; // x: &i32
let &[&mut [ref a]] = &[&mut [42]]; // x: &i32
let (&i, &j, [s]) = &(42, &mut [String::from("🦀")]); // i: i32, j: i32, s: &String
let &(i, j, [ref s]) = &(42, &mut [String::from("🦀")]); // i: i32, j: i32, s: &String
let &(i, j, &mut [ref s]) = &(42, &mut [String::from("🦀")]); // i: i32, j: i32, s: &String
```
#### Patterns that work only without this rule
@ -356,7 +356,6 @@ let &[[&mut a]] = &[&mut [42]]; // x: i32
```rust
//! Edition ≥ 2024: works with or without this rule (alternatives to above)
// No need to abandon match ergonomics
let &[[&a]] = &[&mut [42]]; // x: i32
let &[&mut [a]] = &[&mut [42]]; // x: i32
```
@ -468,8 +467,8 @@ concerns with certain proposals for "deref patterns".
[future-possibilities]: #future-possibilities
- An explicit syntax for mutable by-reference bindings should be chosen at some
point, along with removing the prohibition on implicitly by-reference
mutable bindings.
point, along with removing the prohibition on implicitly by-reference mutable
bindings.
- Future changes to reference types (partial borrows, language sugar for `Pin`,
etc) may interact with match ergonomics.
@ -484,8 +483,7 @@ question that would need to be resolved is whether and how deref patterns
## Matching `&mut` behind `&`
There is one notable situation where match ergonomics cannot be used, and
explicit `ref` is required. Notably, this can occur where `&mut` is nested
behind `&`:
explicit `ref` is required. This happens where `&mut` is nested behind `&`:
```rust
// No way to avoid the `ref`, even with this RFC