Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::useless_conversion: useless conversion to the same type: `std::string::String`

What it meansChecks for Into, TryInto, From, TryFrom, or IntoIterator calls which uselessly convert to the same type. It is in the complexity group and warns by default.

What you see

warning: useless conversion to the same type: `std::string::String`
 --> main.rs:4:17
  |
4 | let s: String = format!("hello").into();
  |                 ^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `format!("hello")`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#useless_conversion
  = note: `#[warn(clippy::useless_conversion)]` 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?

Redundant code.

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

// format!() returns a `String`
let s: String = format!("hello").into();

Write this instead

let s: String = format!("hello");

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
useless_conversion = "allow"

One run

cargo clippy -- -A clippy::useless-conversion

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

1.45.0added in Rust

Clippy's own documentation

What it does

Checks for Into, TryInto, From, TryFrom, or IntoIterator calls which uselessly convert to the same type.

Why is this bad?

Redundant code.

Example

// format!() returns a `String`
let s: String = format!("hello").into();

Use instead:

let s: String = format!("hello");

Past names

identity_conversion

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

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