From 0448441418579ef34259c18026ca1857b17e2a8f Mon Sep 17 00:00:00 2001
From: Alexis Sellier <alexis@radicle.xyz>
Date: Thu, 24 Nov 2022 19:10:32 +0100
Subject: [PATCH] Use `merge` as the `Semilattice` join method

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>
---
 radicle-crdt/src/lib.rs        | 15 ++++++++++++---
 radicle-crdt/src/lwwmap.rs     |  3 +--
 radicle-crdt/src/lwwreg.rs     | 10 ++--------
 radicle-crdt/src/lwwset.rs     |  6 ++----
 radicle-crdt/src/ord.rs        |  6 ++----
 radicle-crdt/src/redactable.rs | 11 ++---------
 6 files changed, 21 insertions(+), 30 deletions(-)

diff --git a/radicle-crdt/src/lib.rs b/radicle-crdt/src/lib.rs
index e6d46cda..2d3afc58 100644
--- a/radicle-crdt/src/lib.rs
+++ b/radicle-crdt/src/lib.rs
@@ -15,9 +15,18 @@ mod test;
 ////////////////////////////////////////////////////////////////////////////////
 
 /// A join-semilattice.
-pub trait Semilattice {
-    /// Join or "merge" two semilattices into one.
-    fn join(self, other: Self) -> Self;
+pub trait Semilattice: Sized {
+    /// Merge an other semilattice into this one.
+    ///
+    /// This operation should obbey the semilattice laws and should thus be idempotent,
+    /// associative and commutative.
+    fn merge(&mut self, other: Self);
+
+    /// Like [`Semilattice::merge`] but takes and returns a new semilattice.
+    fn join(mut self, other: Self) -> Self {
+        self.merge(other);
+        self
+    }
 }
 
 /// Reduce an iterator of semilattice values to its least upper bound.
diff --git a/radicle-crdt/src/lwwmap.rs b/radicle-crdt/src/lwwmap.rs
index c42aa5ce..6792eb38 100644
--- a/radicle-crdt/src/lwwmap.rs
+++ b/radicle-crdt/src/lwwmap.rs
@@ -90,7 +90,7 @@ where
     V: PartialOrd + Eq,
     C: Ord + Copy + Default,
 {
-    fn join(mut self, other: Self) -> Self {
+    fn merge(&mut self, other: Self) {
         for (k, v) in other.inner.into_iter() {
             match self.inner.entry(k) {
                 Entry::Occupied(mut e) => {
@@ -101,7 +101,6 @@ where
                 }
             }
         }
-        self
     }
 }
 
diff --git a/radicle-crdt/src/lwwreg.rs b/radicle-crdt/src/lwwreg.rs
index 7f6dd67e..78a4eff2 100644
--- a/radicle-crdt/src/lwwreg.rs
+++ b/radicle-crdt/src/lwwreg.rs
@@ -33,10 +33,6 @@ impl<T: PartialOrd, C: PartialOrd> LWWReg<T, C> {
         let (t, c) = self.inner.into_inner();
         (c, t)
     }
-
-    pub fn merge(&mut self, other: Self) {
-        self.inner.merge(other.inner);
-    }
 }
 
 impl<T, C> Semilattice for LWWReg<T, C>
@@ -44,10 +40,8 @@ where
     T: PartialOrd + Default,
     C: PartialOrd + Default,
 {
-    fn join(self, other: Self) -> Self {
-        Self {
-            inner: self.inner.join(other.inner),
-        }
+    fn merge(&mut self, other: Self) {
+        self.inner.merge(other.inner);
     }
 }
 
diff --git a/radicle-crdt/src/lwwset.rs b/radicle-crdt/src/lwwset.rs
index 1a722ad3..adc6bd97 100644
--- a/radicle-crdt/src/lwwset.rs
+++ b/radicle-crdt/src/lwwset.rs
@@ -61,10 +61,8 @@ where
     T: Ord,
     C: Ord + Copy + Default,
 {
-    fn join(self, other: Self) -> Self {
-        Self {
-            inner: self.inner.join(other.inner),
-        }
+    fn merge(&mut self, other: Self) {
+        self.inner.merge(other.inner);
     }
 }
 
diff --git a/radicle-crdt/src/ord.rs b/radicle-crdt/src/ord.rs
index ed254724..a3109d4a 100644
--- a/radicle-crdt/src/ord.rs
+++ b/radicle-crdt/src/ord.rs
@@ -57,11 +57,9 @@ impl<T> From<T> for Max<T> {
 }
 
 impl<T: PartialOrd> Semilattice for Max<T> {
-    fn join(self, other: Self) -> Self {
+    fn merge(&mut self, other: Self) {
         if other.0 > self.0 {
-            other
-        } else {
-            self
+            self.0 = other.0;
         }
     }
 }
diff --git a/radicle-crdt/src/redactable.rs b/radicle-crdt/src/redactable.rs
index 73ffbd62..de404717 100644
--- a/radicle-crdt/src/redactable.rs
+++ b/radicle-crdt/src/redactable.rs
@@ -19,8 +19,8 @@ impl<T> From<Option<T>> for Redactable<T> {
     }
 }
 
-impl<T: PartialOrd> Redactable<T> {
-    pub fn merge(&mut self, other: Self) {
+impl<T: PartialOrd> Semilattice for Redactable<T> {
+    fn merge(&mut self, other: Self) {
         match (&self, other) {
             (Self::Redacted, _) => {}
             (Self::Present(_), Self::Redacted) => {
@@ -35,13 +35,6 @@ impl<T: PartialOrd> Redactable<T> {
     }
 }
 
-impl<T: PartialOrd> Semilattice for Redactable<T> {
-    fn join(mut self, other: Self) -> Self {
-        self.merge(other);
-        self
-    }
-}
-
 #[cfg(test)]
 mod test {
     use quickcheck_macros::quickcheck;