Use of a = b.clone() instead of a.clone_from(&b)

[laralove143]

What it does

Catches the places where clone_from could be used instead

Lint Name

clone_from_candidate

Category

pedantic

Advantage

From the docs

• a.clone_from(&b) is equivalent to a = b.clone() in functionality, but can be overridden to reuse the resources of a to avoid unnecessary allocations.

Drawbacks

I can't think of any

Example

let mut a = "a".to_owned();
let b = "b".to_owned();
a = b.clone();
drop(b);

Could be written as:

let mut a = "a".to_owned();
let b = "b".to_owned();
a.clone_from(&b);
drop(b);

[danielrab]

the snippet of code provided doesn't exactly work, but using b.clone_into(&mut a); instead of a.clone_from(b); does.

[Alexendoo]

It would be good if the lint could check if the type has a provided fn clone_from, if it's using the default from Clone the suggestion wouldn't change anything

[laralove143]

the snippet of code provided doesn't exactly work, but using b.clone_into(&mut a); instead of a.clone_from(b); does.

Fixed it

[laralove143]

It would be good if the lint could check if the type has a provided fn clone_from, if it's using the default from Clone the suggestion wouldn't change anything

There's no downsides to it and an upside so I'd say this is always more preferable

[y21]

This was implemented in #12077

Output for the example

warning: assigning the result of `Clone::clone()` may be inefficient
 --> src/main.rs:5:5
  |
5 |     a = b.clone();
  |     ^^^^^^^^^^^^^ help: use `clone_from()`: `a.clone_from(&b)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assigning_clones
  = note: `#[warn(clippy::assigning_clones)]` on by default