Clippy lint · Performance · checked with Clippy 0.1.99

clippy::redundant_allocation: Checks for usage of redundant allocations anywhere in the code

What it meansChecks for usage of redundant allocations anywhere in the code. It is in the performance group and warns by default.

Does it matter?

Expressions such as Rc<&T>, Rc<Rc<T>>, Rc<Arc<T>>, Rc<Box<T>>, Arc<&T>, Arc<Rc<T>>, Arc<Arc<T>>, Arc<Box<T>>, Box<&T>, Box<Rc<T>>, Box<Arc<T>>, Box<Box<T>>, add an unnecessary level of indirection.

Code that could be written to run faster. Warns by default.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

fn foo(bar: Rc<&usize>) {}

Write this instead

fn foo(bar: &usize) {}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
redundant_allocation = "allow"

One run

cargo clippy -- -A clippy::redundant-allocation

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.

Settings in clippy.toml

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

Performancegroup

warndefault level

nofixed by cargo clippy --fix

1.44.0added in Rust

Clippy's own documentation

What it does

Checks for usage of redundant allocations anywhere in the code.

Why is this bad?

Expressions such as Rc<&T>, Rc<Rc<T>>, Rc<Arc<T>>, Rc<Box<T>>, Arc<&T>, Arc<Rc<T>>, Arc<Arc<T>>, Arc<Box<T>>, Box<&T>, Box<Rc<T>>, Box<Arc<T>>, Box<Box<T>>, add an unnecessary level of indirection.

Example

fn foo(bar: Rc<&usize>) {}

Better:

fn foo(bar: &usize) {}

Configuration

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

(default: true)

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

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