crdts 7.3.2

Practical, serializable, thoroughly tested CRDTs
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129

use core::convert::Infallible;
use core::fmt::Debug;

use num::bigint::BigUint;
use serde::{Deserialize, Serialize};

use crate::{CmRDT, CvRDT, Dot, ResetRemove, VClock};

/// `GCounter` is a grow-only witnessed counter.
///
/// # Examples
///
/// ```
/// use crdts::{GCounter, CmRDT};
///
/// let mut a = GCounter::new();
/// let mut b = GCounter::new();
///
/// a.apply(a.inc("A"));
/// b.apply(b.inc("B"));
///
/// assert_eq!(a.read(), b.read());
///
/// a.apply(a.inc("A"));
/// assert!(a.read() > b.read());
/// ```
#[derive(Debug, PartialEq, Eq, Clone, Hash, Serialize, Deserialize)]
pub struct GCounter<A: Ord> {
    inner: VClock<A>,
}

impl<A: Ord> Default for GCounter<A> {
    fn default() -> Self {
        Self {
            inner: Default::default(),
        }
    }
}

impl<A: Ord + Clone + Debug> CmRDT for GCounter<A> {
    type Op = Dot<A>;
    type Validation = Infallible;

    fn validate_op(&self, _op: &Self::Op) -> Result<(), Self::Validation> {
        Ok(())
    }

    fn apply(&mut self, op: Self::Op) {
        self.inner.apply(op)
    }
}

impl<A: Ord + Clone + Debug> CvRDT for GCounter<A> {
    type Validation = Infallible;

    fn validate_merge(&self, _other: &Self) -> Result<(), Self::Validation> {
        Ok(())
    }

    fn merge(&mut self, other: Self) {
        self.inner.merge(other.inner);
    }
}

impl<A: Ord> ResetRemove<A> for GCounter<A> {
    fn reset_remove(&mut self, clock: &VClock<A>) {
        self.inner.reset_remove(clock);
    }
}

impl<A: Ord + Clone> GCounter<A> {
    /// Produce a new `GCounter`.
    pub fn new() -> Self {
        Default::default()
    }

    /// Generate Op to increment the counter.
    pub fn inc(&self, actor: A) -> Dot<A> {
        self.inner.inc(actor)
    }

    /// Generate Op to increment the counter by a number of steps.
    pub fn inc_many(&self, actor: A, steps: u64) -> Dot<A> {
        let steps = steps + self.inner.get(&actor);
        Dot::new(actor, steps)
    }

    /// Return the current sum of this counter.
    pub fn read(&self) -> BigUint {
        self.inner.iter().map(|dot| dot.counter).sum()
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_basic_by_one() {
        let mut a = GCounter::new();
        let mut b = GCounter::new();
        a.apply(a.inc("A"));
        b.apply(b.inc("B"));

        assert_eq!(a.read(), b.read());
        assert_ne!(a, b);

        a.apply(a.inc("A"));

        assert_eq!(a.read(), b.read() + BigUint::from(1u8));
    }

    #[test]
    fn test_basic_by_many() {
        let mut a = GCounter::new();
        let mut b = GCounter::new();
        let steps = 3;

        a.apply(a.inc_many("A", steps));
        b.apply(b.inc_many("B", steps));

        assert_eq!(a.read(), b.read());
        assert_ne!(a, b);

        a.apply(a.inc_many("A", steps));

        assert_eq!(a.read(), b.read() + BigUint::from(steps));
    }
}