Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::default_constructed_unit_structs: Checks for construction on unit struct using default

What it meansChecks for construction on unit struct using default. It is in the complexity group and warns by default.

Does it matter?

This adds code complexity and an unnecessary function call.

Code that does something simple in a complicated way. 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

#[derive(Default)]
struct S<T> {
    _marker: PhantomData<T>
}

let _: S<i32> = S {
    _marker: PhantomData::default()
};

Write this instead

struct S<T> {
    _marker: PhantomData<T>
}

let _: S<i32> = S {
    _marker: PhantomData
};

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
default_constructed_unit_structs = "allow"

One run

cargo clippy -- -A clippy::default-constructed-unit-structs

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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.71.0added in Rust

Clippy's own documentation

What it does

Checks for construction on unit struct using default.

Why is this bad?

This adds code complexity and an unnecessary function call.

Example

#[derive(Default)]
struct S<T> {
    _marker: PhantomData<T>
}

let _: S<i32> = S {
    _marker: PhantomData::default()
};

Use instead:

struct S<T> {
    _marker: PhantomData<T>
}

let _: S<i32> = S {
    _marker: PhantomData
};

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

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