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Co-authored-by: Guillaume Gomez <guillaume1.gomez@gmail.com>
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Matthew Kelly 2022-08-19 09:34:20 -04:00 committed by GitHub
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19
compiler/rustc_error_codes/src/error_codes/E0311.md
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@ -1,9 +1,9 @@
E0311 occurs when there is insufficient information for the rust compiler to
This error occurs when there is insufficient information for the rust compiler to
prove that some time has a long enough lifetime.
Erroneous code example:
```compile_fail, E0311
```compile_fail,E0311
use std::borrow::BorrowMut;
trait NestedBorrowMut<U, V> {
@ -13,7 +13,7 @@ trait NestedBorrowMut<U, V> {
impl<T, U, V> NestedBorrowMut<U, V> for T
where
T: BorrowMut<U>,
U: BorrowMut<V>, // missing lifetime specifier here --> compile fail
U: BorrowMut<V>, // error: missing lifetime specifier
{
fn nested_borrow_mut(&mut self) -> &mut V {
self.borrow_mut().borrow_mut()
@ -21,12 +21,11 @@ where
}
```
In this example we have a trait that borrows some inner data element of type V
from an outer type T, through an intermediate type U. The compiler is unable to
prove that the livetime of U is long enough to support the reference, so it
throws E0311. To fix the issue we can explicitly add lifetime specifiers to the
trait, which link the lifetimes of the various data types and allow the code
to compile.
In this example we have a trait that borrows some inner data element of type `V`
from an outer type `T`, through an intermediate type `U`. The compiler is unable to
prove that the livetime of `U` is long enough to support the reference. To fix the
issue we can explicitly add lifetime specifiers to the `NestedBorrowMut` trait, which
link the lifetimes of the various data types and allow the code to compile.
Working implementation of the `NestedBorrowMut` trait:
@ -40,7 +39,7 @@ trait NestedBorrowMut<'a, U, V> {
impl<'a, T, U, V> NestedBorrowMut<'a, U, V> for T
where
T: BorrowMut<U>,
U: BorrowMut<V> + 'a,
U: BorrowMut<V> + 'a, // Adding lifetime specifier
{
fn nested_borrow_mut(&'a mut self) -> &'a mut V {
self.borrow_mut().borrow_mut()