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Rollup merge of rust-lang#33533 - GuillaumeGomez:add_E0500, r=stevekl…
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…abnik

Add E0500 error explanation

r? @Manishearth

Part of rust-lang#32777.
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eddyb committed May 13, 2016
2 parents 76794b6 + 7a9f4c2 commit e141d95
Showing 1 changed file with 47 additions and 1 deletion.
48 changes: 47 additions & 1 deletion src/librustc_borrowck/diagnostics.rs
Original file line number Diff line number Diff line change
Expand Up @@ -378,6 +378,53 @@ let c = &i; // still ok!
```
"##,

E0500: r##"
A borrowed variable was used in another closure. Example of erroneous code:
```compile_fail
fn you_know_nothing(jon_snow: &mut i32) {
let nights_watch = || {
*jon_snow = 2;
};
let starks = || {
*jon_snow = 3; // error: closure requires unique access to `jon_snow`
// but it is already borrowed
};
}
In here, `jon_snow` is already borrowed by the `nights_watch` closure, so it
cannot be borrowed by the `starks` closure at the same time. To fix this issue,
you can put the closure in its own scope:
```
fn you_know_nothing(jon_snow: &mut i32) {
{
let nights_watch = || {
*jon_snow = 2;
};
} // At this point, `jon_snow` is free.
let starks = || {
*jon_snow = 3;
};
}
```
Or, if the type implements the `Clone` trait, you can clone it between
closures:
```
fn you_know_nothing(jon_snow: &mut i32) {
let mut jon_copy = jon_snow.clone();
let nights_watch = || {
jon_copy = 2;
};
let starks = || {
*jon_snow = 3;
};
}
```
"##,

E0501: r##"
This error indicates that a mutable variable is being used while it is still
captured by a closure. Because the closure has borrowed the variable, it is not
Expand Down Expand Up @@ -857,7 +904,6 @@ fn main() {
register_diagnostics! {
E0385, // {} in an aliasable location
E0388, // {} in a static location
E0500, // closure requires unique access to `..` but .. is already borrowed
E0502, // cannot borrow `..`.. as .. because .. is also borrowed as ...
E0503, // cannot use `..` because it was mutably borrowed
E0505, // cannot move out of `..` because it is borrowed
Expand Down

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