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Implements experimental diff with optimized moves calculation to produce only minimal required moves
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‎CHANGELOG.md‎

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@@ -7,6 +7,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
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### Enhancements
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- Implemented experimental diff with optimized moves calculation to produce only minimal required moves, enabled by `IGListExperimentOptimizedMoves` option. [Nickolay Tarbayev](https://github.com/tarbayev) [(#1139)](https://github.com/Instagram/IGListKit/pull/1139)
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- Add support for UICollectionView's interactive reordering in iOS 9+. Updates include `-[IGListSectionController canMoveItemAtIndex:]` to enable the behavior, `-[IGListSectionController moveObjectFromIndex:toIndex:]` called when items within a section controller were moved through reordering, `-[IGListAdapterDataSource listAdapter:moveObject:from:to]` called when section controllers themselves were reordered (only possible when all section controllers contain exactly 1 object), and `-[IGListUpdatingDelegate moveSectionInCollectionView:fromIndex:toIndex]` to enable custom updaters to conform to the reordering behavior. The update also includes two new examples `ReorderableSectionController` and `ReorderableStackedViewController` to demonstrate how to enable interactive reordering in your client app. [Jared Verdi](https://github.com/jverdi) [(#976)](https://github.com/Instagram/IGListKit/pull/976)
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- 5x improvement to diffing performance when result is only inserts or deletes. [Ryan Nystrom](https://github.com/rnystrom) [(tbd)](tbd)

‎IGListKit.xcodeproj/project.pbxproj‎

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@@ -7,6 +7,9 @@
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objects = {
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/* Begin PBXBuildFile section */
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0179E635207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */; };
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0179E636207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */; };
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0179E637207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */; };
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0B3B92DA1E08D7F5008390ED /* IGListKit.h in Headers */ = {isa = PBXBuildFile; fileRef = 0B3B928B1E08D7F5008390ED /* IGListKit.h */; settings = {ATTRIBUTES = (Public, ); }; };
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0B3B92DB1E08D7F5008390ED /* IGListKit.h in Headers */ = {isa = PBXBuildFile; fileRef = 0B3B928B1E08D7F5008390ED /* IGListKit.h */; settings = {ATTRIBUTES = (Public, ); }; };
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0B3B92F61E08D7F5008390ED /* IGListAdapter.h in Headers */ = {isa = PBXBuildFile; fileRef = 0B3B929A1E08D7F5008390ED /* IGListAdapter.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -407,6 +410,7 @@
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/* End PBXContainerItemProxy section */
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/* Begin PBXFileReference section */
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0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = IGListDiffExperimentOptimizedMovesTests.m; sourceTree = "<group>"; };
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08F0B0FD0690F4FC46DDF21B /* Pods-IGListKit-tvOSTests.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-IGListKit-tvOSTests.release.xcconfig"; path = "Pods/Target Support Files/Pods-IGListKit-tvOSTests/Pods-IGListKit-tvOSTests.release.xcconfig"; sourceTree = "<group>"; };
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0B3B928B1E08D7F5008390ED /* IGListKit.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = IGListKit.h; sourceTree = "<group>"; };
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0B3B929A1E08D7F5008390ED /* IGListAdapter.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = IGListAdapter.h; sourceTree = "<group>"; };
@@ -975,6 +979,7 @@
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294AC6311DDE4C19002FCE5D /* IGListDiffResultTests.m */,
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88144EE61D870EDC007C7F66 /* IGListDiffSwiftTests.swift */,
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88144EE81D870EDC007C7F66 /* IGListDiffTests.m */,
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0179E634207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m */,
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88144EE91D870EDC007C7F66 /* IGListDisplayHandlerTests.m */,
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29DA5CA21EA7C72400113926 /* IGListGenericSectionControllerTests.m */,
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88144EEB1D870EDC007C7F66 /* IGListKitTests-Bridging-Header.h */,
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files = (
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298DDA381E3B168E00F76F50 /* IGLayoutTestItem.m in Sources */,
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885FE2361DC51B76009CE2B4 /* IGListStackSectionControllerTests.m in Sources */,
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0179E636207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
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885FE2311DC51B76009CE2B4 /* IGListDisplayHandlerTests.m in Sources */,
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298DDA3B1E3B16F800F76F50 /* IGLayoutTestDataSource.m in Sources */,
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29C474901DDF460500AE68CE /* IGListSectionMapTests.m in Sources */,
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294AC6321DDE4C19002FCE5D /* IGListDiffResultTests.m in Sources */,
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88144F141D870EDC007C7F66 /* IGListTestOffsettingLayout.m in Sources */,
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8240C7FB1DC2F6CF00B3AAE7 /* IGListTestAdapterStoryboardDataSource.m in Sources */,
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0179E635207FA8EB0082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
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298DDA011E3AE28000F76F50 /* IGTestDiffingObject.m in Sources */,
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88144F131D870EDC007C7F66 /* IGListTestAdapterDataSource.m in Sources */,
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88144F071D870EDC007C7F66 /* IGListAdapterE2ETests.m in Sources */,
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isa = PBXSourcesBuildPhase;
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buildActionMask = 2147483647;
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files = (
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0179E637207FA8F30082DFE6 /* IGListDiffExperimentOptimizedMovesTests.m in Sources */,
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88DF898A1E010F7000B1B9B4 /* IGListDiffTests.m in Sources */,
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88DF89891E010F6500B1B9B4 /* IGListDiffSwiftTests.swift in Sources */,
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882BC1321E0118CB0083B311 /* IGTestObject.m in Sources */,

‎Source/Common/IGListDiff.mm‎

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@@ -94,6 +94,123 @@ static void addIndexToCollection(BOOL useIndexPaths, __unsafe_unretained id coll
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return paths;
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}
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// Calculates longest increasing indexes set using O(n log n) complexity algorithm
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static NSIndexSet *longestIncreasingIndexes(const vector<IGListRecord> &newResultsArray)
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{
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NSUInteger count = newResultsArray.size();
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vector<NSUInteger> prevIndexes(count);
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vector<NSUInteger> indexes(count + 1);
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NSUInteger length = 0;
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for (NSUInteger i = 0; i < count; i++) {
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// Binary search for the largest positive j ≤ length
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// such that X[M[j]] < X[i]
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NSUInteger lo = 1;
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NSUInteger hi = length;
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while (lo <= hi) {
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auto mid = lo + (hi - lo) / 2;
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if (newResultsArray[indexes[mid]].index < newResultsArray[i].index) {
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lo = mid + 1;
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} else {
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hi = mid - 1;
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}
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}
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// After searching, lo is 1 greater than the
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// length of the longest prefix of X[i]
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auto newLength = lo;
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// The predecessor of X[i] is the last index of
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// the subsequence of length newLength-1
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prevIndexes[i] = indexes[newLength - 1];
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indexes[newLength] = i;
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if (newLength > length) {
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// If we found a subsequence longer than any we've
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// found yet, update L
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length = newLength;
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}
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}
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// Reconstruct the longest increasing indexes
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NSMutableIndexSet *result = [NSMutableIndexSet new];
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auto k = indexes[length];
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for (NSUInteger i = 0; i < length; i++) {
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NSUInteger index = newResultsArray[k].index;
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// Ignore inserted entries
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if (index != NSNotFound) {
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[result addIndex:index];
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}
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k = prevIndexes[k];
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}
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return result;
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}
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static BOOL mapContainsMoves(const unordered_map<NSUInteger, NSUInteger> &movesMap, NSUInteger fromIndex, NSUInteger toIndex)
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{
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auto iter = movesMap.find(fromIndex);
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return iter != movesMap.end() && iter->second == toIndex;
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}
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class IGListMoveChecker {
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public:
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virtual bool isMove(const NSInteger oldIndex,
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const NSInteger newIndex,
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const NSInteger insertOffset,
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const NSInteger deleteOffset) {
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return (oldIndex - deleteOffset + insertOffset) != newIndex;
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}
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virtual ~IGListMoveChecker() {}
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};
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class IGListOptimalMoveChecker : public IGListMoveChecker {
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NSIndexSet *longestIncreasingSequence;
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// track previously made moves
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unordered_map<NSUInteger, NSUInteger> moves;
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// track offsets for previously made moves to identify unnecessary moves
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NSInteger movesOffset = 0;
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public:
180+
IGListOptimalMoveChecker(const vector<IGListRecord> &newResultsArray)
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: longestIncreasingSequence(
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// Calculate longest increasing indexes, identifying entries which do not require any moves
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longestIncreasingIndexes(newResultsArray))
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{}
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virtual bool isMove(const NSInteger oldIndex,
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const NSInteger newIndex,
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const NSInteger insertOffset,
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const NSInteger deleteOffset) override {
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auto oldIndexNoDeletes = oldIndex - deleteOffset;
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auto oldCorrectedIndex = oldIndexNoDeletes + insertOffset;
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// 1. if the indexes match, ignore the index, else
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// 2. if the index requires no move and is not swap move, ignore the index, else
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// 3. if the index matches old index with moves offset, ignore the index, else
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if (oldCorrectedIndex != newIndex
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&& (![longestIncreasingSequence containsIndex:oldIndex] || mapContainsMoves(moves, newIndex + deleteOffset - insertOffset, oldIndexNoDeletes))
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&& ((oldCorrectedIndex + movesOffset) != newIndex)) {
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// store move for later checks
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moves[oldIndex] = newIndex;
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// track offset caused by the move
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movesOffset++;
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return true;
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}
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return false;
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}
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};
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static id IGListDiffing(BOOL returnIndexPaths,
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NSInteger fromSection,
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NSInteger toSection,
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addIndexToMap(returnIndexPaths, fromSection, i, oldArray[i], oldMap);
263380
}
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aligned_union<0, IGListMoveChecker, IGListOptimalMoveChecker>::type moveCheckerBuf;
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IGListMoveChecker *moveChecker = IGListExperimentEnabled(experiments, IGListExperimentOptimizedMoves)
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? new (&moveCheckerBuf) IGListOptimalMoveChecker(newResultsArray)
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: new (&moveCheckerBuf) IGListMoveChecker();
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// reset and track offsets from inserted items to calculate where items have moved
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runningOffset = 0;
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@@ -280,10 +404,12 @@ static id IGListDiffing(BOOL returnIndexPaths,
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}
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282406
// calculate the offset and determine if there was a move
283-
// if the indexes match, ignore the index
284407
const NSInteger insertOffset = insertOffsets[i];
285408
const NSInteger deleteOffset = deleteOffsets[oldIndex];
286-
if ((oldIndex - deleteOffset + insertOffset) != i) {
409+
410+
if (moveChecker->isMove(oldIndex, i, insertOffset, deleteOffset)) {
411+
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// add move from old index to new index
287413
id move;
288414
if (returnIndexPaths) {
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NSIndexPath *from = [NSIndexPath indexPathForItem:oldIndex inSection:fromSection];
@@ -299,6 +425,8 @@ static id IGListDiffing(BOOL returnIndexPaths,
299425
addIndexToMap(returnIndexPaths, toSection, i, newArray[i], newMap);
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}
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428+
moveChecker->~IGListMoveChecker();
429+
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NSCAssert((oldCount + [mInserts count] - [mDeletes count]) == newCount,
303431
@"Sanity check failed applying %li inserts and %lu deletes to old count %lu equaling new count %li",
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(long)oldCount, (unsigned long)[mInserts count], (unsigned long)[mDeletes count], (long)newCount);

‎Source/Common/IGListExperiments.h‎

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Original file line numberDiff line numberDiff line change
@@ -26,6 +26,8 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
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IGListExperimentFasterVisibleSectionController = 1 << 4,
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/// Test deduping item-level updates.
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IGListExperimentDedupeItemUpdates = 1 << 5,
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/// Test optimized moves to minimal required number
30+
IGListExperimentOptimizedMoves = 1 << 6,
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};
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/**

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