Crate beef

Faster, more compact implementation of Cow.

Changelog - Cargo - Repository

use beef::Cow;

let borrowed: Cow<str> = Cow::borrowed("Hello");
let owned: Cow<str> = Cow::owned(String::from("World"));

assert_eq!(
    format!("{} {}!", borrowed, owned),
    "Hello World!",
);

There are two versions of Cow exposed by this crate:

• beef::Cow is 3 words wide: pointer, length, and capacity. It stores the ownership tag in capacity.
• beef::lean::Cow is 2 words wide, storing length, capacity, and the ownership tag all in one word.

Both versions are leaner than the std::borrow::Cow:

use std::mem::size_of;

const WORD: usize = size_of::<usize>();

assert_eq!(size_of::<std::borrow::Cow<str>>(), 4 * WORD);
assert_eq!(size_of::<beef::Cow<str>>(), 3 * WORD);

// Lean variant is two words on 64-bit architecture
#[cfg(target_pointer_width = "64")]
assert_eq!(size_of::<beef::lean::Cow<str>>(), 2 * WORD);

Modules

generic

This module contains the actual, albeit generic, implementaiton of the Cow, and the traits that are available to it.

lean

Type Definitions

Cow

Compact three word Cow that puts the ownership tag in capacity. This is a type alias, for documentation see beef::generic::Cow.