Crate hashcow

HashCow

HashCow is a HashMap implementation with copy-on-write keys and values.

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Originally built for optimizing the Purple Protocol, this library provides a way to link HashMaps in memory that have duplicate entries. Instead of the duplicate data, it is instead borrowed and it is only cloned when mutation is needed.

Using HashCow

use hashcow::{Form, CowHashMap};

let mut hm: CowHashMap<str, [u8]> = CowHashMap::new();

// We insert an owned value in the map
hm.insert_owned("key".to_owned(), vec![1, 2, 3]);
assert_eq!(hm.entry_form(&"key").unwrap(), Form::Owned);

// We now create a clone with borrowed fields
let mut hm_clone = hm.borrow_fields();
assert_eq!(hm_clone.entry_form(&"key").unwrap(), Form::Borrowed);

// On mutation, the borrowed entry is cloned
let entry = hm_clone.get_mut(&"key").unwrap();

// We now mutate the cloned value
*entry = vec![4, 5, 6];
assert_eq!(hm_clone.entry_form(&"key").unwrap(), Form::Owned);

// The two maps now have different entries for the same key
assert_eq!(hm.get(&"key").unwrap(), &[1, 2, 3]);
assert_eq!(hm_clone.get(&"key").unwrap(), &[4, 5, 6]);

Contributing

We welcome anyone wishing to contribute to HashCow! Check out the [issues section][issues] of the repository before starting out.

License

HashCow is licensed under the MIT license.

Macros

count	Counts the number of values passed to it.
set	Returns a HashSet containing the passed values.

Structs

CowHashMap

A HashMap data-structure with copy-on-write keys and values.

Enums

Form	The form of the entry in the map. Can be either Borrowed or Owned.