Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::multi_assignments: assignments don't nest intuitively

What it meansChecks for nested assignments. It is in the suspicious group and warns by default.

What you see

warning: assignments don't nest intuitively
 --> main.rs:3:1
  |
3 | a = b = 42;
  | ^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#multi_assignments
  = note: `#[warn(clippy::multi_assignments)]` 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?

While this is in most cases already a type mismatch, the result of an assignment being () can throw off people coming from languages like python or C, where such assignments return a copy of the assigned value.

Code that is most likely wrong or useless. Warns by default.

How to fix it

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

Flagged

a = b = 42;

Write this instead

b = 42;
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::multi_assignments)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
multi_assignments = "allow"

One run

cargo clippy -- -A clippy::multi-assignments

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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.65.0added in Rust

Clippy's own documentation

What it does

Checks for nested assignments.

Why is this bad?

While this is in most cases already a type mismatch, the result of an assignment being () can throw off people coming from languages like python or C, where such assignments return a copy of the assigned value.

Example

a = b = 42;

Use instead:

b = 42;
a = b;

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

Up next

Also worth your time

Did this answer your question?