Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::ref_patterns: usage of ref pattern

What it meansChecks for usages of the ref keyword. It is in the restriction group and off by default.

What you see

warning: usage of ref pattern
 --> main.rs:4:13
  |
4 | if let Some(ref foo) = opt {}
  |             ^^^^^^^
  |
  = help: consider using `&` for clarity instead
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#ref_patterns
  = note: requested on the command line with `-W clippy::ref-patterns`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

The ref keyword can be confusing for people unfamiliar with it, and often it is more concise to use & instead.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

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

Flagged

let opt = Some(5);
if let Some(ref foo) = opt {}

Write this instead

let opt = Some(5);
if let Some(foo) = &opt {}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
ref_patterns = "warn"

In code

#![warn(clippy::ref_patterns)]

One run

cargo clippy -- -W clippy::ref-patterns

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.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.71.0added in Rust

Clippy's own documentation

What it does

Checks for usages of the ref keyword.

Why restrict this?

The ref keyword can be confusing for people unfamiliar with it, and often it is more concise to use & instead.

Example

let opt = Some(5);
if let Some(ref foo) = opt {}

Use instead:

let opt = Some(5);
if let Some(foo) = &opt {}

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

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