Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::unnecessary_mut_passed: Detects passing a mutable reference to a function that only requires an immutable reference
What it meansDetects passing a mutable reference to a function that only requires an immutable reference. It is in the style group and warns by default.
Does it matter?
The mutable reference rules out all other references to the value. Also the code misleads about the intent of the call site.
Code that works but is not idiomatic Rust. 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
vec.push(&mut value);
Write this instead
vec.push(&value);
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::unnecessary_mut_passed)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
unnecessary_mut_passed = "allow"One run
cargo clippy -- -A clippy::unnecessary-mut-passedThe [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.
Clippy's own documentation
What it does
Detects passing a mutable reference to a function that only requires an immutable reference.
Why is this bad?
The mutable reference rules out all other references to the value. Also the code misleads about the intent of the call site.
Example
vec.push(&mut value);
Use instead:
vec.push(&value);
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- needless_returnunneeded `return` statement
- new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
- len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
- unnecessary_foldthis `.fold` can be written more succinctly using another method
- unnecessary_lazy_evaluationsunnecessary closure used to substitute value for `Option::None`
- unnecessary_map_orthis `map_or` can be simplified
- unnecessary_owned_empty_stringsusage of `&String::new()` for a function expecting a `&str` argument
- unneeded_struct_patternstruct pattern is not needed for a unit variant
- unsafe_removed_from_nameChecks for imports that remove “unsafe” from an item’s name
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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