manual-retain

Prefer retain over replacing an owned array with its filtered result

Assigning an owned array's filtered result back to the same place allocates replacement storage.
Instead, you SHOULD call retain to remove rejected elements from the owned array in place.

- Category: performance
- Level: warning
- Fix: suggestion
- Scope: module

Reported

function keepPositive(input: ^int32[]): ^int32[] {
    let values = input;
    values = values.filter((value) => value > 0);
    return values;
}
Accepted

function keepPositive(input: ^int32[]): ^int32[] {
    let values = input;
    values.retain((value) => value > 0);
    return values;
}
Prior art

- Clippy · manualretain

language/linter/src/rules/performance/manualretain.rs:8