Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::useless_asref: Checks for usage of .as_ref() or .as_mut() where the types before and after the call are the same

What it meansChecks for usage of .as_ref() or .as_mut() where the types before and after the call are the same. It is in the complexity group and warns by default.

Does it matter?

The call is unnecessary.

Code that does something simple in a complicated way. Warns by default.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

let x: &[i32] = &[1, 2, 3, 4, 5];
do_stuff(x.as_ref());

Write this instead

let x: &[i32] = &[1, 2, 3, 4, 5];
do_stuff(x);

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
useless_asref = "allow"

One run

cargo clippy -- -A clippy::useless-asref

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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for usage of .as_ref() or .as_mut() where the types before and after the call are the same.

Why is this bad?

The call is unnecessary.

Example

let x: &[i32] = &[1, 2, 3, 4, 5];
do_stuff(x.as_ref());

The correct use would be:

let x: &[i32] = &[1, 2, 3, 4, 5];
do_stuff(x);

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

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