Remove the Equatable requirement on components.

Bento.xcodeproj/project.pbxproj

@@ -36,8 +36,6 @@
 		58FC4427207CF2BB00DA3614 /* AnyRenderableTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A3EF77F205D866F00D043AC /* AnyRenderableTests.swift */; };
 		58FC4428207CF2BB00DA3614 /* TestId.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A784702205EB61D00FA597E /* TestId.swift */; };
 		58FC4429207CF2BB00DA3614 /* TestRenderable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A784700205EB5E000FA597E /* TestRenderable.swift */; };
-		58FC442A207CF2BB00DA3614 /* NodeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A7846FC205EAF7C00FA597E /* NodeTests.swift */; };
-		58FC442B207CF2BB00DA3614 /* SectionTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A7846FE205EAF8400FA597E /* SectionTests.swift */; };
 		58FC442F207CF37700DA3614 /* script in Resources */ = {isa = PBXBuildFile; fileRef = 58FC442E207CF37700DA3614 /* script */; };
 		58FC4430207CF3CD00DA3614 /* Bento.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 58BA755C2016303B0050D5F1 /* Bento.framework */; };
 		58FC4431207CF3CD00DA3614 /* Bento.framework in Embed Frameworks */ = {isa = PBXBuildFile; fileRef = 58BA755C2016303B0050D5F1 /* Bento.framework */; settings = {ATTRIBUTES = (CodeSignOnCopy, RemoveHeadersOnCopy, ); }; };
@@ -76,7 +74,7 @@
 		740921B820ACE5EC00B59F5C /* ConcatenationTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 740921B720ACE5EC00B59F5C /* ConcatenationTests.swift */; };
 		74208FA12083B1F00062CC8D /* Nimble.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 74208FA22083B1F00062CC8D /* Nimble.framework */; };
 		747523C72083A6660030CCAA /* FlexibleDiff.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 747523C82083A6660030CCAA /* FlexibleDiff.framework */; };
-		9A4DB3E1212CB3710079D5AE /* Changeset+MutationIndexPairs.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A4DB3E0212CB3710079D5AE /* Changeset+MutationIndexPairs.swift */; };
+		9A4DB3E1212CB3710079D5AE /* ChangesetExtensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9A4DB3E0212CB3710079D5AE /* ChangesetExtensions.swift */; };
 		9AF4786A21205E3100F87E21 /* Supplement.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9AF4786921205E3100F87E21 /* Supplement.swift */; };
 		9AF4786C2120CA7500F87E21 /* BentoReusableView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9AF4786B2120CA7500F87E21 /* BentoReusableView.swift */; };
 		A67A873520B5D2D100BC2BAC /* RenderableTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = A67A873420B5D2D100BC2BAC /* RenderableTests.swift */; };
@@ -170,6 +168,7 @@
 		58FC4440207CFBD700DA3614 /* MovieComponentView.xib */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = file.xib; path = MovieComponentView.xib; sourceTree = "<group>"; };
 		58FC444B207CFBE100DA3614 /* BookAppointmentViewController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = BookAppointmentViewController.swift; sourceTree = "<group>"; };
 		58FC444C207CFBE200DA3614 /* MoviesListViewController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MoviesListViewController.swift; sourceTree = "<group>"; };
+		5B175A6421C0634800590F34 /* ComponentContract.md */ = {isa = PBXFileReference; lastKnownFileType = net.daringfireball.markdown; path = ComponentContract.md; sourceTree = "<group>"; };
 		61B40916208523F50063DE25 /* IntroViewModel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = IntroViewModel.swift; sourceTree = "<group>"; };
 		61B40917208523F50063DE25 /* IntroViewController.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = IntroViewController.swift; sourceTree = "<group>"; };
 		61B64BB02086561B0092082C /* IntroRenderer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IntroRenderer.swift; sourceTree = "<group>"; };
@@ -192,10 +191,8 @@
 		74208FA22083B1F00062CC8D /* Nimble.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = Nimble.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		747523C82083A6660030CCAA /* FlexibleDiff.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = FlexibleDiff.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		9A3EF77F205D866F00D043AC /* AnyRenderableTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AnyRenderableTests.swift; sourceTree = "<group>"; };
-		9A4DB3E0212CB3710079D5AE /* Changeset+MutationIndexPairs.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Changeset+MutationIndexPairs.swift"; sourceTree = "<group>"; };
+		9A4DB3E0212CB3710079D5AE /* ChangesetExtensions.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChangesetExtensions.swift; sourceTree = "<group>"; };
 		9A7846FA205D89C000FA597E /* XCTest.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = XCTest.framework; path = Platforms/iPhoneOS.platform/Developer/Library/Frameworks/XCTest.framework; sourceTree = DEVELOPER_DIR; };
-		9A7846FC205EAF7C00FA597E /* NodeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NodeTests.swift; sourceTree = "<group>"; };
-		9A7846FE205EAF8400FA597E /* SectionTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SectionTests.swift; sourceTree = "<group>"; };
 		9A784700205EB5E000FA597E /* TestRenderable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TestRenderable.swift; sourceTree = "<group>"; };
 		9A784702205EB61D00FA597E /* TestId.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TestId.swift; sourceTree = "<group>"; };
 		9AF4786921205E3100F87E21 /* Supplement.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Supplement.swift; sourceTree = "<group>"; };
@@ -251,9 +248,10 @@
 		581ED77E2022041C00EC9584 /* Diff */ = {
 			isa = PBXGroup;
 			children = (
+				5B175A6421C0634800590F34 /* ComponentContract.md */,
 				58467B02202B33F200577C77 /* TableViewSectionDiff.swift */,
 				61B64BB320873DA10092082C /* CollectionViewSectionDiff.swift */,
-				9A4DB3E0212CB3710079D5AE /* Changeset+MutationIndexPairs.swift */,
+				9A4DB3E0212CB3710079D5AE /* ChangesetExtensions.swift */,
 			);
 			path = Diff;
 			sourceTree = "<group>";
@@ -374,8 +372,6 @@
 			children = (
 				A67A873420B5D2D100BC2BAC /* RenderableTests.swift */,
 				9A3EF77F205D866F00D043AC /* AnyRenderableTests.swift */,
-				9A7846FC205EAF7C00FA597E /* NodeTests.swift */,
-				9A7846FE205EAF8400FA597E /* SectionTests.swift */,
 				740921B520ACDDDA00B59F5C /* IfTests.swift */,
 				740921B720ACE5EC00B59F5C /* ConcatenationTests.swift */,
 				9A784700205EB5E000FA597E /* TestRenderable.swift */,
@@ -660,7 +656,7 @@
 				65E3ECAC2113591500869DF3 /* FocusableView.swift in Sources */,
 				A9509880661501C40B50E453 /* TableViewHeaderFooterView.swift in Sources */,
 				515F94097C1F82B7E5C2DE0C /* Section.swift in Sources */,
-				9A4DB3E1212CB3710079D5AE /* Changeset+MutationIndexPairs.swift in Sources */,
+				9A4DB3E1212CB3710079D5AE /* ChangesetExtensions.swift in Sources */,
 				65E3ECA421133BF700869DF3 /* FocusEligibilitySource.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -670,11 +666,9 @@
 			buildActionMask = 2147483647;
 			files = (
 				58FC4427207CF2BB00DA3614 /* AnyRenderableTests.swift in Sources */,
-				58FC442A207CF2BB00DA3614 /* NodeTests.swift in Sources */,
 				58FC4428207CF2BB00DA3614 /* TestId.swift in Sources */,
 				58FC4429207CF2BB00DA3614 /* TestRenderable.swift in Sources */,
 				740921B620ACDDDA00B59F5C /* IfTests.swift in Sources */,
-				58FC442B207CF2BB00DA3614 /* SectionTests.swift in Sources */,
 				740921B820ACE5EC00B59F5C /* ConcatenationTests.swift in Sources */,
 				A67A873520B5D2D100BC2BAC /* RenderableTests.swift in Sources */,
 			);

Bento/Bento/Node.swift

@@ -1,6 +1,6 @@
 import UIKit
 
-public struct Node<Identifier: Hashable>: Equatable {
+public struct Node<Identifier: Hashable> {
     public let id: Identifier
     let component: AnyRenderable
 
@@ -13,10 +13,6 @@ public struct Node<Identifier: Hashable>: Equatable {
         self.init(id: id, component: AnyRenderable(component))
     }
 
-    public static func == (lhs: Node, rhs: Node) -> Bool {
-        return lhs.id == rhs.id && lhs.component == rhs.component
-    }
-
     public func component<T>(as type: T.Type) -> T? {
         return component.cast(to: type)
     }

Bento/Bento/Section.swift

@@ -1,6 +1,6 @@
 import UIKit
 
-public struct Section<SectionID: Hashable, ItemID: Hashable>: Equatable {
+public struct Section<SectionID: Hashable, ItemID: Hashable> {
     public typealias Item = Node<ItemID>
 
     public let id: SectionID
@@ -70,16 +70,6 @@ public struct Section<SectionID: Hashable, ItemID: Hashable>: Equatable {
         return supplements[supplement]?.sizeBoundTo(size: size, inheritedMargins: inheritedMargins)
     }
 
-    public static func hasEqualMetadata(_ lhs: Section, _ rhs: Section) -> Bool {
-        return lhs.supplements == rhs.supplements
-    }
-
-    public static func == (lhs: Section, rhs: Section) -> Bool {
-        return lhs.id == rhs.id
-            && hasEqualMetadata(lhs, rhs)
-            && lhs.items == rhs.items
-    }
-
     public static func |---+ (lhs: Section, rhs: Item) -> Section {
         return Section(id: lhs.id, items: lhs.items + [rhs], supplements: lhs.supplements)
     }

Bento/Bento/UITableViewExtensions.swift

@@ -59,3 +59,16 @@ extension UITableView {
         return objc_getAssociatedObject(self, AssociatedKey.adapter) as AnyObject?
     }
 }
+
+extension UITableView {
+    var visibleSections: Set<Int> {
+        let isVisible = (0 ..< numberOfSections)
+            .map(rect(forSection:))
+            .map(bounds.intersects)
+
+        return Set(
+            zip(isVisible, 0 ..< numberOfSections)
+                .compactMap { $0 ? $1 : nil }
+        )
+    }
+}

Bento/Diff/ChangesetExtensions.swift

@@ -0,0 +1,19 @@
+import FlexibleDiff
+
+extension Changeset {
+    /// Retrieve the positions of all mutated items, in place or moved. The changes are filtered
+    /// by the specified collection of pre-removal visible item indices.
+    ///
+    /// - parameters:
+    ///   - visibleItems: The pre-removal indices of the visible items.
+    func positionsOfMutations<Indices: Collection>(amongVisible visibleItems: Indices) -> FlattenCollection<[[(source: Int, destination: Int)]]> where Indices.Element == Int {
+        return [
+            mutations.lazy
+                .filter(visibleItems.contains)
+                .map { (source: $0, destination: $0) },
+            moves.lazy
+                .filter { visibleItems.contains($0.source) }
+                .map { (source: $0.source, destination: $0.destination) }
+        ].joined()
+    }
+}

Bento/Diff/CollectionViewSectionDiff.swift

@@ -15,13 +15,16 @@ struct CollectionViewSectionDiff<SectionID: Hashable, ItemID: Hashable> {
     }
 
     func apply(to collectionView: UICollectionView, completion: (() -> Void)? = nil) {
+        /// Since we are going to always rebind visible components, there is no point to evaluate
+        /// component equation. However, we still force all instances of components to be treated as
+        /// unequal, so as to preserve all positional information for in-place updates to visible cells.
         let diff = SectionedChangeset(previous: oldSections,
                                       current: newSections,
                                       sectionIdentifier: { $0.id },
-                                      areMetadataEqual: Section.hasEqualMetadata,
+                                      areMetadataEqual: const(false),
                                       items: { $0.items },
                                       itemIdentifier: { $0.id },
-                                      areItemsEqual: ==)
+                                      areItemsEqual: const(false))
         apply(diff: diff, to: collectionView, completion: completion)
     }
 
@@ -40,7 +43,7 @@ struct CollectionViewSectionDiff<SectionID: Hashable, ItemID: Hashable> {
                 by: { $0.section }
             )
 
-            for (source, destination) in diff.sections.mutationIndexPairs {
+            for (source, destination) in diff.sections.positionsOfMutations(amongVisible: groups.keys) {
                 if let indexPaths = groups[source] {
                     for indexPath in indexPaths {
                         let view = collectionView.supplementaryView(forElementKind: elementKind, at: indexPath)
@@ -95,8 +98,13 @@ extension UICollectionView {
             deleteItems(at: sectionMutation.deletedIndexPaths)
             insertItems(at: sectionMutation.insertedIndexPaths)
             perform(moves: sectionMutation.movedCollectionIndexPaths)
+
+            let visibleItems = Set(
+                indexPathsForVisibleItems
+                    .compactMap { $0.section == sectionMutation.source ? $0.row : nil }
+            )
 
-            for (source, destination) in sectionMutation.changeset.mutationIndexPairs {
+            for (source, destination) in sectionMutation.changeset.positionsOfMutations(amongVisible: visibleItems) {
                 if let cell = cellForItem(at: [sectionMutation.source, source]) as? CollectionViewContainerCell {
                     let component = newSections[sectionMutation.destination]
                         .items[destination]

Bento/Diff/ComponentContract.md

@@ -0,0 +1,17 @@
+## Bento Component Contract
+Applicable to both UICollectionView and UITableView.
+
+### Components must conform to `Renderable`.
+`Renderable` represents a set of requirements which a component must satisfy for Bento to integrate it.
+
+### Components need not be evaluable for equation.
+Bento enforces no restriction in what types of properties the component can comprise of. Moreover, there are also prevalent uses of non-equatable properties, for example, user interaction callbacks. Therefore, Bento does not require any component to be evaluable for equation.
+
+### Any given ID path may be bound with any kind and instance of components at any time.
+Bento is designed to be very flexible in terms of component types. Users should require no extra precaution in populating their `Box`es with different permutations of ID paths and components.
+
+### Visible ID paths may be aggressively rebound.
+[As Bento cannot rely on component equation](#components-need-not-be-evaluable-for-equation), Bento aggressively rebinds all visible ID paths with the new component at the same ID path in any new `Box` being applied.
+
+### Components should avoid deriving animations from rebinding occurrences.
+[Given potential occurrences of aggressive rebinding](#visible-id-paths-may-be-aggressively-rebound), rebinding is generally not a good indiction of when animations should happen. Components might want to instead have data-driven, fine-grained animations, or rely on mechanisms like `ViewLifecycleAware`. 

Bento/Diff/TableViewSectionDiff.swift

@@ -15,19 +15,25 @@ struct TableViewSectionDiff<SectionId: Hashable, RowId: Hashable> {
     }
 
     func apply(to tableView: UITableView) {
+        /// Since we are going to always rebind visible components, there is no point to evaluate
+        /// component equation. However, we still force all instances of components to be treated as
+        /// unequal, so as to preserve all positional information for in-place updates to visible cells.
         let diff = SectionedChangeset(previous: oldSections,
                                       current: newSections,
                                       sectionIdentifier: { $0.id },
-                                      areMetadataEqual: Section.hasEqualMetadata,
+                                      areMetadataEqual: const(false),
                                       items: { $0.items },
                                       itemIdentifier: { $0.id },
-                                      areItemsEqual: ==)
+                                      areItemsEqual: const(false))
         apply(diff: diff, to: tableView)
     }
 
     private func apply(diff: SectionedChangeset, to tableView: UITableView) {
         tableView.beginUpdates()
-        for (source, destination) in diff.sections.mutationIndexPairs {
+
+        let visibleSections = tableView.visibleSections
+
+        for (source, destination) in diff.sections.positionsOfMutations(amongVisible: visibleSections) {
             if let headerView = tableView.headerView(forSection: source) {
                let component = newSections[destination].supplements[.header]
                 (headerView as? BentoReusableView)?.bind(component)
@@ -38,6 +44,7 @@ struct TableViewSectionDiff<SectionId: Hashable, RowId: Hashable> {
                 (footerView as? BentoReusableView)?.bind(component)
             }
         }
+
         tableView.insertSections(diff.sections.inserts, with: animation.sectionInsertion)
         tableView.deleteSections(diff.sections.removals, with: animation.sectionDeletion)
         tableView.moveSections(diff.sections.moves, animation: animation)
@@ -48,14 +55,22 @@ struct TableViewSectionDiff<SectionId: Hashable, RowId: Hashable> {
     private func apply(sectionMutations: [SectionedChangeset.MutatedSection],
                        to tableView: UITableView,
                        with animation: TableViewAnimation) {
+        let visibleIndexPaths = tableView.indexPathsForVisibleRows ?? []
+
         for sectionMutation in sectionMutations {
             tableView.deleteRows(at: sectionMutation.deletedIndexPaths, with: animation.rowDeletion)
             tableView.insertRows(at: sectionMutation.insertedIndexPaths, with: animation.rowInsertion)
             tableView.perform(moves: sectionMutation.movedIndexPaths)
 
-            for (source, destination) in sectionMutation.changeset.mutationIndexPairs {
-                if let cell = tableView.cellForRow(at: [sectionMutation.source, source]) as? BentoReusableView {
-                    let node = newSections[sectionMutation.destination].items[destination]
+            let visibleRows = Set(
+                visibleIndexPaths.lazy
+                    .filter { $0.section == sectionMutation.source }
+                    .map { $0.item }
+            )
+
+            for (source, destination) in sectionMutation.changeset.positionsOfMutations(amongVisible: visibleRows) {
+                if let cell = tableView.cellForRow(at: IndexPath(item: source, section: sectionMutation.source)) as? BentoReusableView {
+                   let node = newSections[sectionMutation.destination].items[destination]
                     cell.bind(node.component)
                 }
             }

Bento/Helpers.swift

@@ -42,3 +42,7 @@ internal func search<T>(from leaf: UIView, type: T.Type) -> T? {
     }
     return cell as! T?
 }
+
+func const<T, U, Value>(_ value: Value) -> (_: T, _: U) -> Value {
+    return { _, _ in value }
+}

Bento/Renderable/AnyRenderable.swift

@@ -58,10 +58,6 @@ struct AnyRenderable: Renderable {
 
         return view
     }
-
-    static func ==(lhs: AnyRenderable, rhs: AnyRenderable) -> Bool {
-        return lhs.base.equals(to: rhs.base)
-    }
 }
 
 private class AnyRenderableBox<Base: Renderable>: AnyRenderableBoxBase where Base.View: UIView {
@@ -91,12 +87,6 @@ private class AnyRenderableBox<Base: Renderable>: AnyRenderableBoxBase where Bas
     override func cast<T>(to type: T.Type) -> T? {
         return base as? T
     }
-
-    override func equals(to other: AnyRenderableBoxBase) -> Bool {
-        guard let other = other as? AnyRenderableBox<Base>
-            else { return false }
-        return self.base == other.base
-    }
 }
 
 private class AnyRenderableBoxBase {
@@ -108,6 +98,5 @@ private class AnyRenderableBoxBase {
 
     func render(in view: UIView) { fatalError() }
     func generate() -> UIView { fatalError() }
-    func equals(to other: AnyRenderableBoxBase) -> Bool { fatalError() }
     func cast<T>(to type: T.Type) -> T? { fatalError() }
 }