⚡ Bolt: Batch @Published array updates to prevent UI re-renders

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-04-13 - Batch @Published array mutations
+**Learning:** In SwiftUI `ObservableObject` view models, mutating individual elements of a `@Published` array property inside a loop triggers a UI update notification for every change. This can cause severe performance issues when selecting/deselecting large lists.
+**Action:** For collections of value types (structs), always utilize functional methods like `.map` to batch updates into a single property assignment, significantly reducing unnecessary UI recalculations. Always add comments explaining this optimization to prevent future developers from 'optimizing' it back to a standard `for` loop, as `.map` can appear slower in standard Swift contexts.

Sources/Cacheout/ViewModels/CacheoutViewModel.swift

@@ -171,15 +171,26 @@ class CacheoutViewModel: ObservableObject {
         }
     }
 
+    // ⚡ Bolt: Batching array updates using .map instead of mutating elements in a loop.
+    // Mutating individual elements of a @Published array inside a loop triggers a UI
+    // update for every change. Using .map to assign a new array at once batches these
+    // updates into a single UI recalculation, improving performance on large lists.
+
     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 +204,29 @@ 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
+        }
     }
 
     /// Menu bar label: show free GB in the tray