84 lines
2.4 KiB
Rust
84 lines
2.4 KiB
Rust
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use serde::{Deserialize, Serialize};
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use crate::crdt::crdt::*;
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/// Simple CRDT Map
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///
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/// This types defines a CRDT for a map from keys to values. Values are CRDT types which
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/// can have their own updating logic.
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///
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/// Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
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/// This is why the key type `K` must implement `Ord` (and also to ensure a unique serialization,
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/// such that two values can be compared for equality based on their hashes). As a consequence,
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/// insertions take `O(n)` time. This means that Map should be used for reasonably small maps.
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/// However, note that even if we were using a more efficient data structure such as a `BTreeMap`,
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/// the serialization cost `O(n)` would still have to be paid at each modification, so we are
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/// actually not losing anything here.
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#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
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pub struct Map<K, V> {
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vals: Vec<(K, V)>,
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}
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impl<K, V> Map<K, V>
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where
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K: Clone + Ord,
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V: Clone + CRDT,
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{
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/// Create a new empty map CRDT
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pub fn new() -> Self {
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Self { vals: vec![] }
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}
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/// Returns a map that contains a single mapping from the specified key to the specified value.
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/// This can be used to build a delta-mutator:
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/// when merged with another map, the value will be added or CRDT-merged if a previous
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/// value already exists.
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pub fn put_mutator(k: K, v: V) -> Self {
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Self { vals: vec![(k, v)] }
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}
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pub fn put(&mut self, k: K, v: V) {
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self.merge(&Self::put_mutator(k, v));
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}
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/// Removes all values from the map
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pub fn clear(&mut self) {
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self.vals.clear();
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}
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/// Get a reference to the value assigned to a key
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pub fn get(&self, k: &K) -> Option<&V> {
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match self.vals.binary_search_by(|(k2, _)| k2.cmp(&k)) {
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Ok(i) => Some(&self.vals[i].1),
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Err(_) => None,
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}
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}
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/// Gets a reference to all of the items, as a slice. Usefull to iterate on all map values.
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pub fn items(&self) -> &[(K, V)] {
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&self.vals[..]
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}
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/// Returns the number of items in the map
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pub fn len(&self) -> usize {
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self.vals.len()
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}
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}
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impl<K, V> CRDT for Map<K, V>
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where
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K: Clone + Ord,
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V: Clone + CRDT,
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{
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fn merge(&mut self, other: &Self) {
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for (k, v2) in other.vals.iter() {
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match self.vals.binary_search_by(|(k2, _)| k2.cmp(&k)) {
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Ok(i) => {
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self.vals[i].1.merge(&v2);
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}
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Err(i) => {
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self.vals.insert(i, (k.clone(), v2.clone()));
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}
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}
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}
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}
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}
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