Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::suspicious_to_owned: Checks for the usage of _.to_owned(), on a Cow<'_, _>

What it meansChecks for the usage of _.to_owned(), on a Cow<'_, _>. It is in the suspicious group and warns by default.

Does it matter?

Calling to_owned() on a Cow creates a clone of the Cow itself, without taking ownership of the Cow contents (i.e. it’s equivalent to calling Cow::clone). The similarly named into_owned method, on the other hand, clones the Cow contents, effectively turning any Cow::Borrowed into a Cow::Owned. Given the potential ambiguity, consider replacing to_owned with clone for better readability or, if getting a Cow::Owned was the original intent, using into_owned instead.

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

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

let s = "Hello world!";
let cow = Cow::Borrowed(s);

let data = cow.to_owned();
assert!(matches!(data, Cow::Borrowed(_)))

Write this instead

let s = "Hello world!";
let cow = Cow::Borrowed(s);

let data = cow.clone();
assert!(matches!(data, Cow::Borrowed(_)))

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
suspicious_to_owned = "allow"

One run

cargo clippy -- -A clippy::suspicious-to-owned

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 the usage of _.to_owned(), on a Cow<'_, _>.

Why is this bad?

Calling to_owned() on a Cow creates a clone of the Cow itself, without taking ownership of the Cow contents (i.e. it’s equivalent to calling Cow::clone). The similarly named into_owned method, on the other hand, clones the Cow contents, effectively turning any Cow::Borrowed into a Cow::Owned.

Given the potential ambiguity, consider replacing to_owned with clone for better readability or, if getting a Cow::Owned was the original intent, using into_owned instead.

Example

let s = "Hello world!";
let cow = Cow::Borrowed(s);

let data = cow.to_owned();
assert!(matches!(data, Cow::Borrowed(_)))

Use instead:

let s = "Hello world!";
let cow = Cow::Borrowed(s);

let data = cow.clone();
assert!(matches!(data, Cow::Borrowed(_)))

let s = "Hello world!";
let cow = Cow::Borrowed(s);

let _data: String = cow.into_owned();

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

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