⚡ Bolt: Optimize SwiftUI View Model Array Batching

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-05-15 - Batched `@Published` Array Updates
+**Learning:** Mutating individual elements of a `@Published` array inside a `for` loop triggers a UI update notification for every single element change. For collections of structs, using `.map` to create a new array and assigning it back batches the UI update into a single event.
+**Action:** Always use functional methods like `.map` instead of `for` loops when performing bulk modifications on `@Published` value-type collections in SwiftUI ViewModels, and add explanatory comments to prevent future regressions.

Sources/Cacheout/ViewModels/CacheoutViewModel.swift

@@ -172,14 +172,24 @@ class CacheoutViewModel: ObservableObject {
     }
 
     func selectAllSafe() {
-        for i in scanResults.indices where scanResults[i].category.riskLevel == .safe && !scanResults[i].isEmpty {
-            scanResults[i].isSelected = true
+        // Optimization: Use .map to batch updates and trigger only ONE UI notification.
+        // Mutating elements inside a loop triggers a notification for EVERY element changed.
+        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
+        // Optimization: Use .map to batch updates and trigger only ONE UI notification.
+        // Mutating elements inside a loop triggers a notification for EVERY element changed.
+        scanResults = scanResults.map { result in
+            var updated = result
+            updated.isSelected = false
+            return updated
         }
         deselectAllNodeModules()
     }
@@ -193,17 +203,35 @@ class CacheoutViewModel: ObservableObject {
     }
 
     func selectStaleNodeModules() {
-        for i in nodeModulesItems.indices where nodeModulesItems[i].isStale {
-            nodeModulesItems[i].isSelected = true
+        // Optimization: Use .map to batch updates and trigger only ONE UI notification.
+        // Mutating elements inside a loop triggers a notification for EVERY element changed.
+        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 }
+        // Optimization: Use .map to batch updates and trigger only ONE UI notification.
+        // Mutating elements inside a loop triggers a notification for EVERY element changed.
+        nodeModulesItems = nodeModulesItems.map { item in
+            var updated = item
+            updated.isSelected = true
+            return updated
+        }
     }
 
     func deselectAllNodeModules() {
-        for i in nodeModulesItems.indices { nodeModulesItems[i].isSelected = false }
+        // Optimization: Use .map to batch updates and trigger only ONE UI notification.
+        // Mutating elements inside a loop triggers a notification for EVERY element changed.
+        nodeModulesItems = nodeModulesItems.map { item in
+            var updated = item
+            updated.isSelected = false
+            return updated
+        }
     }
 
     /// Menu bar label: show free GB in the tray