False positive #12828
Description
Summary
Right now clippy complains about cloning Option<Rc<_>> with as_ref().map(Rc::clone).
In this particular case I believe this is justified approach to use explicit Rc::clone. It helps to harden code to make sure no deep clone would happen in case of future changes. I believe the same logic applies to Arc.
By using
Rc::clonefor reference counting, we can visually distinguish between the deep-copy kinds of clones and the kinds of clones that increase the reference count. When looking for performance problems in the code, we only need to consider the deep-copy clones and can disregard calls toRc::clone.
https://doc.rust-lang.org/book/ch15-04-rc.html#using-rct-to-share-data
Lint Name
clippy::useless_asref
Reproducer
I tried this code:
use std::rc::Rc;
fn main() {
let value: Option<Rc<Vec<u8>>> = Some(Rc::new(vec![]));
let _rc_clone = value.as_ref().map(Rc::clone);
}I saw this happen:
warning: this call to `as_ref.map(...)` does nothing
--> src/main.rs:5:21
|
5 | let _rc_clone = value.as_ref().map(Rc::clone);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `value.clone()`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_asref
= note: `#[warn(clippy::useless_asref)]` on by default
I expected to see this happen:
No warnings
Version
rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: aarch64-apple-darwin
release: 1.78.0
LLVM version: 18.1.2
Additional Labels
No response