diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_error_codes/src/error_codes/E0503.md | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0503.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0503.md | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0503.md b/compiler/rustc_error_codes/src/error_codes/E0503.md new file mode 100644 index 000000000..c52525fee --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0503.md @@ -0,0 +1,54 @@ +A value was used after it was mutably borrowed. + +Erroneous code example: + +```compile_fail,E0503 +fn main() { + let mut value = 3; + // Create a mutable borrow of `value`. + let borrow = &mut value; + let _sum = value + 1; // error: cannot use `value` because + // it was mutably borrowed + println!("{}", borrow); +} +``` + +In this example, `value` is mutably borrowed by `borrow` and cannot be +used to calculate `sum`. This is not possible because this would violate +Rust's mutability rules. + +You can fix this error by finishing using the borrow before the next use of +the value: + +``` +fn main() { + let mut value = 3; + let borrow = &mut value; + println!("{}", borrow); + // The block has ended and with it the borrow. + // You can now use `value` again. + let _sum = value + 1; +} +``` + +Or by cloning `value` before borrowing it: + +``` +fn main() { + let mut value = 3; + // We clone `value`, creating a copy. + let value_cloned = value.clone(); + // The mutable borrow is a reference to `value` and + // not to `value_cloned`... + let borrow = &mut value; + // ... which means we can still use `value_cloned`, + let _sum = value_cloned + 1; + // even though the borrow only ends here. + println!("{}", borrow); +} +``` + +For more information on Rust's ownership system, take a look at the +[References & Borrowing][references-and-borrowing] section of the Book. + +[references-and-borrowing]: https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html |