Replace existing HashRing nodes when primary keys match

.changeset/brave-rings-update.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Update existing `HashRing` nodes when adding a value with the same primary key.

packages/effect/src/HashRing.ts

@@ -145,6 +145,7 @@ export const addMany: {
       const key = PrimaryKey.value(node)
       const entry = self.nodes.get(key)
       if (entry) {
+        entry[0] = node
         if (entry[1] === weight) continue
         toRemove ??= new Set()
         toRemove.add(key)

packages/effect/test/HashRing.test.ts

@@ -0,0 +1,47 @@
+import { assert, describe, it } from "@effect/vitest"
+import * as HashRing from "effect/HashRing"
+import * as PrimaryKey from "effect/PrimaryKey"
+
+describe("HashRing", () => {
+  it("updates the stored node when adding the same primary key", () => {
+    const first = {
+      name: "first",
+      [PrimaryKey.symbol]() {
+        return "node"
+      }
+    }
+    const updated = {
+      name: "updated",
+      [PrimaryKey.symbol]() {
+        return "node"
+      }
+    }
+    const ring = HashRing.make<typeof first>()
+
+    HashRing.add(ring, first)
+    HashRing.add(ring, updated)
+
+    assert.strictEqual(HashRing.get(ring, "request"), updated)
+  })
+
+  it("updates the stored node when changing its weight", () => {
+    const first = {
+      name: "first",
+      [PrimaryKey.symbol]() {
+        return "node"
+      }
+    }
+    const updated = {
+      name: "updated",
+      [PrimaryKey.symbol]() {
+        return "node"
+      }
+    }
+    const ring = HashRing.make<typeof first>()
+
+    HashRing.add(ring, first)
+    HashRing.add(ring, updated, { weight: 2 })
+
+    assert.strictEqual(HashRing.get(ring, "request"), updated)
+  })
+})