⚡ Bolt: Batch UI updates for list selections

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-05-18 - Batch Updates for SwiftUI @Published Collections
+**Learning:** Mutating individual elements of a `@Published` array property inside a loop triggers a UI update notification for *every* change. For collections of value types (structs), this causes O(N) view re-evaluations when performing bulk operations like "Select All", leading to significant UI stutter.
+**Action:** Use functional methods like `.map` to batch updates. Transform the array and assign it back to the `@Published` property in a single operation, resulting in exactly one UI update notification. Always add a comment explaining this optimization so it isn't "refactored" back to a loop.

Sources/Cacheout/ViewModels/CacheoutViewModel.swift

@@ -171,15 +171,24 @@ class CacheoutViewModel: ObservableObject {
         }
     }
 
+    // Note: We use .map to batch updates. Mutating individual elements of a @Published array
+    // inside a loop triggers a UI update notification for every change. For collections of
+    // value types, map batches updates into a single property assignment.
     func selectAllSafe() {
-        for i in scanResults.indices where scanResults[i].category.riskLevel == .safe && !scanResults[i].isEmpty {
-            scanResults[i].isSelected = true
+        scanResults = scanResults.map { result in
+            var updated = result
+            if updated.category.riskLevel == .safe && !updated.isEmpty {
+                updated.isSelected = true
+            }
+            return updated
         }
     }
 
     func deselectAll() {
-        for i in scanResults.indices {
-            scanResults[i].isSelected = false
+        scanResults = scanResults.map { result in
+            var updated = result
+            updated.isSelected = false
+            return updated
         }
         deselectAllNodeModules()
     }
@@ -193,17 +202,29 @@ class CacheoutViewModel: ObservableObject {
     }
 
     func selectStaleNodeModules() {
-        for i in nodeModulesItems.indices where nodeModulesItems[i].isStale {
-            nodeModulesItems[i].isSelected = true
+        nodeModulesItems = nodeModulesItems.map { item in
+            var updated = item
+            if updated.isStale {
+                updated.isSelected = true
+            }
+            return updated
         }
     }
 
     func selectAllNodeModules() {
-        for i in nodeModulesItems.indices { nodeModulesItems[i].isSelected = true }
+        nodeModulesItems = nodeModulesItems.map { item in
+            var updated = item
+            updated.isSelected = true
+            return updated
+        }
     }
 
     func deselectAllNodeModules() {
-        for i in nodeModulesItems.indices { nodeModulesItems[i].isSelected = false }
+        nodeModulesItems = nodeModulesItems.map { item in
+            var updated = item
+            updated.isSelected = false
+            return updated
+        }
     }
 
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