Alternative implementation of Cow that's more compact in memory.
```rust use beef::Cow;
let borrowed = Cow::borrowed("Hello"); let owned = Cow::from(String::from("World"));
assert_eq!( format!("{} {}!", borrowed, owned), "Hello World!", );
// beef::Cow is 3 word sized, while std::borrow::Cow is 4 word sized
assert!(std::mem::sizeof::
The standard library Cow is an enum with two variants:
rust
pub enum Cow<'a, B> where
B: 'a + ToOwned + ?Sized,
{
Borrowed(&'a B),
Owned(<B as ToOwned>::Owned),
}
For the most common pairs of values - &str and String, or &[u8] and Vec<u8> - this
means that the entire enum is 4 words wide:
```text Padding | v +----------+----------+----------+----------+ Borrowed: | Tag | Pointer | Length | XXXXXXXX | +----------+----------+----------+----------+
+----------+----------+----------+----------+
Owned: | Tag | Pointer | Length | Capacity | +----------+----------+----------+----------+ ```
Instead of being an enum with a tag, beef::Cow uses capacity to determine whether the
value it's holding is owned (capacity is greater than 0), or borrowed (capacity is 0).