Description
What it does
Warn when an error type (probably by detecting that it has impl std::error::Error and is publicly exported) is over some arbitrary threshold, suggesting boxing the inner data to reduce the size.
Categories (optional)
- Kind:
clippy::perf
Large error types result in a lot of redundant memory copying on the success path when the Ok value is small.
Drawbacks
None.
Example
struct Error {
data: [u8; 512],
}
impl std::error::Error for Error {}Could be written as:
struct Error {
data: Box<[u8; 512]>,
}
impl std::error::Error for Error {}Other
There are two existing related issues: #4652 and #3884. I think this is different because in those cases it detects when you use the error internally with a small success variant; whereas even if internally all usage is with large success variants, a user of the library may be mapping the success variant to something small, ending up hitting one of those lints in their usage and having to box the whole error; while it would be easier for all users if the size was reduced at the source.