Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::explicit_deref_methods: explicit `deref` method call

What it meansChecks for explicit deref() or deref_mut() method calls. Doesn’t lint inside the implementation of the Deref or DerefMut traits. It is in the pedantic group and off by default.

What you see

warning: explicit `deref` method call
 --> main.rs:5:15
  |
5 | let b: &str = a.deref();
  |               ^^^^^^^^^ help: try: `&*a`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#explicit_deref_methods
  = note: `-W clippy::explicit-deref-methods` implied by `-W clippy::pedantic`

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?

Dereferencing by &*x or &mut *x is clearer and more concise, when not part of a method chain.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

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

use std::ops::Deref;
let a: &mut String = &mut String::from("foo");
let b: &str = a.deref();

Write this instead

let a: &mut String = &mut String::from("foo");
let b = &*a;

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]
explicit_deref_methods = "warn"

In code

#![warn(clippy::explicit_deref_methods)]

One run

cargo clippy -- -W clippy::explicit-deref-methods

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.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.44.0added in Rust

Clippy's own documentation

What it does

Checks for explicit deref() or deref_mut() method calls.

Doesn’t lint inside the implementation of the Deref or DerefMut traits.

Why is this bad?

Dereferencing by &*x or &mut *x is clearer and more concise, when not part of a method chain.

Example

use std::ops::Deref;
let a: &mut String = &mut String::from("foo");
let b: &str = a.deref();

Use instead:

let a: &mut String = &mut String::from("foo");
let b = &*a;

This lint excludes all of:

let _ = d.unwrap().deref();
let _ = Foo::deref(&foo);
let _ = <Foo as Deref>::deref(&foo);

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

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