Struct cvrdt_exposition::lww_register::LWWRegister

pub struct LWWRegister<X: Clone + Eq> {
    pub value: X,
    pub timestamp: Instant,
}

A last-write-wins register

Panics

Any attempt to add a new element to this register will panic if the register's timestamp is greater than Instant::now() (no time-traveling allowed) at the time of calling add:

// this will panic
use std::time::{Duration, Instant};
use cvrdt_exposition::{Grow, LWWRegister};
let mut x = LWWRegister::new(('a', Instant::now() + Duration::from_secs(1729)));
x.add('b');

Difference from references

In the comprehensive study paper, timestamps are unsigned integers, whereas we use std::time::Instants.

Examples

Example usage, including demonstrating some properties:

use std::time::Instant;
use cvrdt_exposition::{Grow, LWWRegister};
let mut x = LWWRegister::new(('a', Instant::now()));
x.add('b');
x.add('c');
assert_eq!(x.query(&()), 'c');
let y = LWWRegister::new(('z', Instant::now()));
assert!(x.le(&y));
let z = x.merge(&y);
assert_eq!(y.merge(&x).payload(), z.payload());
assert_eq!(z.query(&()), 'z');
assert_eq!(z.payload().0, 'z');

Fields

value: X

The value saved in this register

timestamp: Instant

The time when this register was last saved

Trait Implementations

impl<X: Clone + Eq> Clone for LWWRegister<X>

fn clone(&self) -> LWWRegister<X>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<X: Debug + Clone + Eq> Debug for LWWRegister<X>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<X: Clone + Eq> Grow for LWWRegister<X>

type Payload = (X, Instant)

The internal state of our CvRDT; sufficient to build a new copy via new. Required to implement Eq for testing and verification.

type Update = X

Message to update our internal state

type Query = ()

Message to query the Value of our CvRDT

type Value = X

The response to a Query

fn new(payload: Self::Payload) -> Self

Create a new version of our data structure from the given Payload

fn payload(&self) -> Self::Payload

Retrieve the Payload (internal state) of this CvRDT

fn add(&mut self, update: Self::Update)

Add an item to the data structure, mutating this CvRDT in place

fn le(&self, other: &Self) -> bool

Is this CvRDT ≤ another in the semilattice's partial order?

fn merge(&self, other: &Self) -> Self

Merge this data structure and another into a new CvRDT

fn query(&self, _query: &Self::Query) -> Self::Value

Query the data structure to get some Value