if let guards documentation
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WaffleLapkin
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| ```rust,ignore | ||
| match expression { | ||
| pattern if let subpattern = guard_expr => arm_body, | ||
| ... | ||
| } | ||
| ``` |
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Would it be possible to make a working example?
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Im not really sure, because it's not stable feature and contains behind #![feature...] gate that's aren't allowed in documentation and CI will fail with this error
Running target/debug/style-check ../src
error in ../src/expressions/match-expr.md: #![feature] attributes are not allowed
| * The `if let` guard may refer to variables bound by the outer match pattern. | ||
| * New variables bound inside the `if let` guard (e.g., `y` in the example above) are available within the body of the match arm where the guard evaluates to `true`, but are not accessible in other arms or outside the match expression. | ||
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| ```rust,ignore |
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| ```rust,ignore | |
| ```rust |
src/expressions/match-expr.md
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| 2. Guard evaluation happens after that, and: | ||
| * It runs using a shared borrow of the scrutinee | ||
| * You cannot move from the scrutinee inside the guard. | ||
| * New bindings created inside the guard (e.g., via `if let Some(y) = expr`) are local to the guard and do not persist into the match arm body. |
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I've updated it and it now should make more sense
| ``` | ||
| > [!NOTE] | ||
| > Unlike regular if guards, `if let` guards execute only once per match arm, even if the pattern uses the `|` operator to match multiple patterns. This avoids repeated evaluation and potential side effects. | ||
| > ```rust,ignore |
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| > ```rust,ignore | |
| > ```rust |
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@WaffleLapkin not sure if you got notifications when i update something, but i update almost all your reviews expect ones that asks to make code runnable, because im not sure if this is possible, we can remove |
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It’s been a while since the original PR for
if letguards was opened, so I decided to take the initiative and push it a bit closer to stabilizationThis PR adds some documentation — I did my best to keep it consistent with the existing docs on
ifguardsThere might still be some rough edges or small inaccuracies, so feel free to point them out
It’s also my first time contributing to the docs, so any feedback is appreciated!
Tracking issue rust-lang/rust#51114
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