-Cannot mutate place in this match guard.
+The matched value was assigned in a match guard.
-When matching on a variable it cannot be mutated in the match guards, as this
-could cause the match to be non-exhaustive:
+Erroneous code example:
```compile_fail,E0510
let mut x = Some(0);
match x {
- None => (),
- Some(_) if { x = None; false } => (),
- Some(v) => (), // No longer matches
+ None => {}
+ Some(_) if { x = None; false } => {} // error!
+ Some(_) => {}
}
```
+When matching on a variable it cannot be mutated in the match guards, as this
+could cause the match to be non-exhaustive.
+
Here executing `x = None` would modify the value being matched and require us
-to go "back in time" to the `None` arm.
+to go "back in time" to the `None` arm. To fix it, change the value in the match
+arm:
+
+```
+let mut x = Some(0);
+match x {
+ None => {}
+ Some(_) => {
+ x = None; // ok!
+ }
+}
+```