Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::assign_op_pattern: manual implementation of an assign operation
What it meansChecks for a = a op b or a = b commutative_op a patterns. It is in the style group and warns by default.
What you see
warning: manual implementation of an assign operation --> main.rs:7:1 | 7 | a = a + b; | ^^^^^^^^^ help: replace it with: `a += b` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#assign_op_pattern = note: `#[warn(clippy::assign_op_pattern)]` on by default
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?
These can be written as the shorter a op= b.
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
let mut a = 5;
let b = 0;
// ...
a = a + b;
Write this instead
let mut a = 5;
let b = 0;
// ...
a += b;
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::assign_op_pattern)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
assign_op_pattern = "allow"One run
cargo clippy -- -A clippy::assign-op-patternThe [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
Checks for a = a op b or a = b commutative_op a
patterns.
Why is this bad?
These can be written as the shorter a op= b.
Known problems
While forbidden by the spec, OpAssign traits may have
implementations that differ from the regular Op impl.
Example
let mut a = 5;
let b = 0;
// ...
a = a + b;
Use instead:
let mut a = 5;
let b = 0;
// ...
a += b;
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
- assertions_on_constantsChecks for assert!(true) and assert!(false) calls
- blocks_in_conditionsChecks for if and match conditions that use blocks containing an expression, statements or conditions that use closures with blocks
- bool_assert_comparisonused `assert_eq!` with a literal bool
- borrow_interior_mutable_constborrow of a named constant with interior mutability
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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