#cow #smart-pointers #serde #borrow #no-std

no-std cervine

A slightly more flexible Cow; roughly to T: Borrow<R> as alloc::borrow::Cow is to B: ToOwned

6 releases

0.0.6 Sep 21, 2020
0.0.5 Sep 10, 2020
0.0.2 Aug 26, 2020

#2071 in Data structures

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97 downloads per month
Used in 8 crates (5 directly)


196 lines


Lib.rs Crates.io Docs.rs

Rust 1.42.0 Build Status Crates.io - License

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A slightly more flexible clone-on-write smart pointer; roughly to T: Borrow<R> as alloc::borrow::Cow is to B: ToOwned.

The owned and reference types can be chosen independently, which means for example smartstring's String can be used in the owned variant instead of alloc's.

Serde support is optional via the "serde" feature and no_std-compatible.
Note that deserialisation currently always happens by value and serde::Serialize is looked up only on the reference type. This may change in a major version upgrade, likely only after specialization becomes available.


Please use cargo-edit to always add the latest version of this library:

cargo add cervine


Same type (T = R = [bool; 2]):

use cervine::Cow;
use rand::prelude::*;
use std::borrow::Borrow as _;

let data = [true, false];
let mut cow = Cow::Borrowed(&data);

if thread_rng().gen() {
  cow = Cow::Owned([false, true]);

let array_ref: &[bool; 2] = cow.borrow();

Different types (T = String and R = str):

use cervine::Cow;
use rand::prelude::*;
use smartstring::alias::String;

let mut cow = Cow::Borrowed("borrowed");

if thread_rng().gen() {
  cow = Cow::Owned(String::from("owned"));

let str_ref: &str = cow.as_ref();


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Code of Conduct



cervine strictly follows Semantic Versioning 2.0.0 with the following exceptions:

  • The minor version will not reset to 0 on major version changes (except for v1).
    Consider it the global feature level.
  • The patch version will not reset to 0 on major or minor version changes (except for v0.1 and v1).
    Consider it the global patch level.

This includes the Rust version requirement specified above.
Earlier Rust versions may be compatible, but this can change with minor or patch releases.

Which versions are affected by features and patches can be determined from the respective headings in CHANGELOG.md.