Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::let_underscore_lock: Checks for let _ = sync_lock

What it meansChecks for let _ = sync_lock. This supports mutex and rwlock in parking_lot. For std locks see the rustc lint let_underscore_lock It is in the correctness group and denied by default (the build fails).

Does it matter?

This statement immediately drops the lock instead of extending its lifetime to the end of the scope, which is often not intended. To extend lock lifetime to the end of the scope, use an underscore-prefixed name instead (i.e. _lock). If you want to explicitly drop the lock, std::mem::drop conveys your intention better and is less error-prone.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let _ = mutex.lock();

Write this instead

let _lock = mutex.lock();

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::let_underscore_lock)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
let_underscore_lock = "allow"

One run

cargo clippy -- -A clippy::let-underscore-lock

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

1.43.0added in Rust

Clippy's own documentation

What it does

Checks for let _ = sync_lock. This supports mutex and rwlock in parking_lot. For std locks see the rustc lint let_underscore_lock

Why is this bad?

This statement immediately drops the lock instead of extending its lifetime to the end of the scope, which is often not intended. To extend lock lifetime to the end of the scope, use an underscore-prefixed name instead (i.e. _lock). If you want to explicitly drop the lock, std::mem::drop conveys your intention better and is less error-prone.

Example

let _ = mutex.lock();

Use instead:

let _lock = mutex.lock();

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

Up next

Also worth your time

Did this answer your question?