Clippy lint · Style · checked with Clippy 0.1.99

clippy::field_reassign_with_default: Checks for immediate reassignment of fields initialized with Default::default()

What it meansChecks for immediate reassignment of fields initialized with Default::default(). It is in the style group and warns by default.

Does it matter?

It’s more idiomatic to use the functional update syntax.

Code that works but is not idiomatic Rust. Warns by default.

How to fix it

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

Flagged

let mut a: A = Default::default();
a.i = 42;

Write this instead

let a = A {
    i: 42,
    .. Default::default()
};

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::field_reassign_with_default)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
field_reassign_with_default = "allow"

One run

cargo clippy -- -A clippy::field-reassign-with-default

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.

Stylegroup

warndefault level

nofixed by cargo clippy --fix

1.49.0added in Rust

Clippy's own documentation

What it does

Checks for immediate reassignment of fields initialized with Default::default().

Why is this bad?

It’s more idiomatic to use the functional update syntax.

Known problems

Assignments to patterns that are of tuple type are not linted.

Example

let mut a: A = Default::default();
a.i = 42;

Use instead:

let a = A {
    i: 42,
    .. Default::default()
};

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

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