From c1e7f11a1a23e00ab683ae33fc7d406ccc75aeef Mon Sep 17 00:00:00 2001
From: Morten Heiberg <morten@heiberg.net>
Date: Tue, 11 Dec 2018 10:26:03 +0100
Subject: [PATCH] Optimization. Ignore empty delta updates. (#5)

---
 .../CollectionViewDataSource.swift             |  2 +-
 Sources/UITableView/TableViewDataSource.swift  |  2 +-
 Sources/Updates.swift                          | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Sources/UICollectionView/CollectionViewDataSource.swift b/Sources/UICollectionView/CollectionViewDataSource.swift
index a446575..be15b58 100644
--- a/Sources/UICollectionView/CollectionViewDataSource.swift
+++ b/Sources/UICollectionView/CollectionViewDataSource.swift
@@ -21,7 +21,7 @@ open class CollectionViewDataSource<DS, VF>: NSObject, UICollectionViewDataSourc
         super.init()
 
         self.subscription = dataSource.updateHandler.subscribe { [weak self] update in
-            guard let `self` = self, !self.ignoreDataSourceUpdates else { return }
+            guard let `self` = self, !update.isEmpty, !self.ignoreDataSourceUpdates else { return }
             viewUpdate(update)
         }
     }
diff --git a/Sources/UITableView/TableViewDataSource.swift b/Sources/UITableView/TableViewDataSource.swift
index aa50f1b..41f6896 100644
--- a/Sources/UITableView/TableViewDataSource.swift
+++ b/Sources/UITableView/TableViewDataSource.swift
@@ -21,7 +21,7 @@ open class TableViewDataSource<DS, VF>: NSObject, UITableViewDataSource where DS
         super.init()
 
         self.subscription = dataSource.updateHandler.subscribe { [weak self] update in
-            guard let `self` = self, !self.ignoreDataSourceUpdates else { return }
+            guard let `self` = self, !update.isEmpty, !self.ignoreDataSourceUpdates else { return }
             viewUpdate(update)
         }
     }
diff --git a/Sources/Updates.swift b/Sources/Updates.swift
index 19ce845..378af7b 100644
--- a/Sources/Updates.swift
+++ b/Sources/Updates.swift
@@ -10,6 +10,24 @@ public enum IndexedUpdate {
         deletedRows: [IndexPath]
     )
     case full
+
+    /// Whether the update is considered empty.
+    ///
+    /// - `true` for delta updates with no content
+    /// - `false` in all other cases
+    public var isEmpty: Bool {
+        switch self {
+        case let .delta(insertedSections, updatedSections, deletedSections, insertedRows, updatedRows, deletedRows):
+            return insertedSections.isEmpty &&
+                updatedSections.isEmpty &&
+                deletedSections.isEmpty &&
+                insertedRows.isEmpty &&
+                updatedRows.isEmpty &&
+                deletedRows.isEmpty
+        case .full:
+            return false
+        }
+    }
 }
 
 public class IndexedUpdateHandler {