Crate maybe_owned_trait
source ·Expand description
Either an owned or borrowed value, with type known at compile time
This crate offers a MaybeOwned
trait which allows you to pass either an owned
or a borrowed value to a function. As opposed to std::borrow::Cow
and beef::Cow
, this trait
- allows you to keep call sites clean, as you don’t need to explicitly construct
Cow
s; - allows you to perform a static dispatch without relying on constant propagation, if possible;
- consequently benefit from various optimizations (notably, dead code elimination and constant propagation), if possible.
However, it also creates additional mental overhead and in some cases might cause genericity-induced problems.
Eventually, definition sites might become cleaner with an attribute proc macro.
Example
use rand::Rng;
use maybe_owned_trait::MaybeOwned;
use std::path::{Path, PathBuf};
// Definition site is a bit more verbose than with `Cow`, yet still reasonable
fn my_fn(path: impl for<'a> MaybeOwned<Owned = PathBuf, Borrowed<'a> = &'a Path>) {
// Of course, you'll have a meaningful condition here
if rand::thread_rng().gen::<bool>() {
let path_buf: PathBuf = path.to_owned();
println!("Owned buf: {:?}", path_buf);
} else {
let path: &Path = path.borrow();
println!("Borrowed path: {:?}", path);
};
}
let path = PathBuf::from("hello");
// Call sites are clean
my_fn(&path);
my_fn(path);
With beef
feature enabled, this crate also provides the implementations of MaybeOwned
for beef::Cow
and beef::lean::Cow
.
Traits
- Either an owned or a borrowed value.