Clippy lints / Performance
Clippy lint · Performance · checked with Clippy 0.1.99
clippy::cmp_owned: Checks for conversions to owned values just for the sake of a comparison
What it meansChecks for conversions to owned values just for the sake of a comparison. It is in the performance group and warns by default.
Does it matter?
The comparison can operate on a reference, so creating an owned value effectively throws it away directly afterwards, which is needlessly consuming code and heap space.
Code that could be written to run faster. 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
if x.to_owned() == y {}
Write this instead
if x == y {}
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::cmp_owned)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
cmp_owned = "allow"One run
cargo clippy -- -A clippy::cmp-ownedThe [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.
Clippy's own documentation
What it does
Checks for conversions to owned values just for the sake of a comparison.
Why is this bad?
The comparison can operate on a reference, so creating an owned value effectively throws it away directly afterwards, which is needlessly consuming code and heap space.
Example
if x.to_owned() == y {}
Use instead:
if x == y {}
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- large_enum_variantlarge size difference between variants
- box_collectionChecks for usage of Box<T> where T is a collection such as Vec anywhere in the code. Check the Box documentation for more information
- boxed_locallocal variable doesn't need to be boxed here
- cloned_ref_to_slice_refsChecks for slice references with cloned references such as &[f.clone()]
- collapsible_str_replaceChecks for consecutive calls to str::replace (2 or more) that can be collapsed into a single call
- double_ended_iterator_lastcalled `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator
- drain_collectdraining all elements of a collection into a new collection of the same type
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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