Lint slice args that could be slices of impl Deref<_>s #7587
Description
What it does
On exported functions, lint function arguments of the following types: &[&str], &[String], &[&[_]], &[Vec<_>] . Suggest using &[impl Deref<Target = str>] and &[impl Deref<Target = [_]>] as appropriate. The lint is subject to the avoid-breaking-exported-api configuration.
Categories (optional)
- Kind: perf
Why is this bad?
&[&str] and &[&[_]] require extra backing space if we already have a Vec<String> or Vec<Vec<_>>. On the other hand, &[String] and &[Vec<_>] require that we allocate to change the type if we actually have a Vec<&str>, a Vec<Cow<'_, str>> or a Vec<Arc<[_]>>`.
Drawbacks
The resulting code is less terse and the generics mean more work for type inference. Worst case some client code might fail to compile because inference no longer gets a clear argument type to work with.
Example
fn takes_strings(strings: &[String]) { todo!() }
fn takes_strs(strs: &[&str]) { todo!() }
fn takes_vecs(vecs: &[Vec<u8>]) { todo!() }
fn takes_slices(slices: &[&[u8]]) { todo!() }Could be written as:
fn takes_strings(strings: &[impl Deref<Target = str>]) { todo!() }
fn takes_strs(strs: &[impl Deref<Target = str>]) { todo!() }
fn takes_vecs(vecs: &[impl Deref<Target = [u8]>]) { todo!() }
fn takes_slices(slices: &[impl Deref<Target = [u8]>]) { todo!() }