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Replace Delta with Snapshot and Changeset. (#33)
* Snapshot and Changeset. * Documentation and reproducibility tests.
1 parent a985798 commit 1501e01

9 files changed

Lines changed: 844 additions & 304 deletions

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‎ReactiveCollections.xcodeproj/project.pbxproj‎

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@@ -154,8 +161,10 @@
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@@ -325,6 +335,7 @@
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‎Sources/Changeset.swift‎

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import Foundation
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/// Represents an atomic batch of changes made to a collection.
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///
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/// A `Changeset` represents changes as **offsets** of elements. You may
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/// subscript a collection of zero-based indexing with the offsets, e.g. `Array`. You must
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/// otherwise convert the offsets into indices before subscripting.
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///
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/// # Implicit order between offsets.
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///
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/// Removal offsets precede insertion offsets. Move offset pairs are semantically
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/// equivalent to a pair of removal offset (source) and an insertion offset (destination).
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///
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/// ## Example: Reproducing an array.
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///
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/// Given a previous version of a collection, a current version of a collection, and a
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/// `Changeset`, we can reproduce the current version by applying the `Changeset` to
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/// the previous version.
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///
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/// - note: `Array` is a zero-based container, thus being able to consume zero-based
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/// offsets directly. If you are working upon non-zero-based or undetermined collection
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/// types, you **must** first convert offsets into indices.
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///
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/// 1. Clone the previous version.
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///
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/// ```
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/// var elements = previous
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/// ```
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///
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/// 2. Copy mutated elements specified by `mutations`.
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///
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/// `mutations` offsets are invariant. So it can simply be conducted as:
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/// ```
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/// for range in changeset.mutations.rangeView {
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/// elements[range] = current[range]
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/// }
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/// ```
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///
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/// 3. Perform removals specified by `removals` and `moves` (sources).
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///
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/// ```
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/// let removals = changeset.removals
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/// .union(IndexSet(changeset.moves.map { $0.source }))
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///
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/// for range in removals.rangeView.reversed() {
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/// elements.removeSubrange(range)
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/// }
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/// ```
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///
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/// 4. Perform inserts specified by `inserts` and `moves` (destinations).
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///
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/// ```
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/// let inserts = changeset.inserts
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/// .union(IndexSet(changeset.moves.map { $0.destination }))
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///
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/// for range in inserts.rangeView {
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/// elements.insert(contentsOf: current[range], at: range.lowerBound)
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/// }
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/// ```
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///
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public struct Changeset {
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/// Represents the context of a move operation applied to a collection.
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public struct Move {
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public let source: Int
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public let destination: Int
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public let isMutated: Bool
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public init(source: Int, destination: Int, isMutated: Bool) {
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(self.source, self.destination, self.isMutated) = (source, destination, isMutated)
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}
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}
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/// The offsets of inserted elements in the current version of the collection.
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///
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/// - important: To obtain the actual index, you must apply
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/// `Collection.index(self:_:offsetBy:)` on the current version, the
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/// start index and the offset.
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public var inserts = IndexSet()
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/// The offsets of removed elements in the previous version of the collection.
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///
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/// - important: To obtain the actual index, you must apply
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/// `Collection.index(self:_:offsetBy:)` on the previous version, the
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/// start index and the offset.
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public var removals = IndexSet()
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/// The offsets of position-invariant mutations that are valid across both versions
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/// of the collection.
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///
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/// `mutations` only implies an invariant relative position. The actual indexes can
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/// be different, depending on the collection type.
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///
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/// If an element has both changed and moved, it is instead included in `moves` with
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/// an asserted mutation flag.
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///
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/// - important: To obtain the actual index, you must apply
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/// `Collection.index(self:_:offsetBy:)` on the relevant versions, the
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/// start index and the offset.
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public var mutations = IndexSet()
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/// The offset pairs of moves with a mutation flag as the associated value.
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///
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/// The source offset is semantically equivalent to a removal offset, while the
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/// destination offset is semantically equivalent to an insertion offset.
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///
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/// - important: To obtain the actual index, you must apply
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/// `Collection.index(self:_:offsetBy:)` on the relevant versions, the
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/// start index and the offset.
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public var moves = [Move]()
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public init() {}
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public init(inserts: IndexSet = [], removals: IndexSet = [], mutations: IndexSet = [], moves: [Move] = []) {
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(self.inserts, self.removals) = (inserts, removals)
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(self.mutations, self.moves) = (mutations, moves)
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}
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public init<C: Collection>(initial: C) {
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inserts = IndexSet(integersIn: 0 ..< Int(initial.count))
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}
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}
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#if !swift(>=3.2)
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extension SignedInteger {
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fileprivate init<I: SignedInteger>(_ integer: I) {
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self.init(integer.toIntMax())
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}
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}
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#endif
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extension Changeset.Move: Equatable {
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public static func == (left: Changeset.Move, right: Changeset.Move) -> Bool {
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return left.isMutated == right.isMutated && left.source == right.source && left.destination == right.destination
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}
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}
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extension Changeset: Equatable {
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public static func == (left: Changeset, right: Changeset) -> Bool {
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return left.inserts == right.inserts && left.removals == right.removals && left.mutations == right.mutations && left.moves == right.moves
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}
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}
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// Better debugging experience
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extension Changeset: CustomDebugStringConvertible {
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public var debugDescription: String {
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func moveDescription(_ move: Move) -> String {
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return "\(move.source) -> \(move.isMutated ? "*" : "")\(move.destination)"
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}
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return ([
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"- inserted \(inserts.count) item(s) at [\(inserts.map(String.init).joined(separator: ", "))]" as String,
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"- deleted \(removals.count) item(s) at [\(removals.map(String.init).joined(separator: ", "))]" as String,
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"- mutated \(mutations.count) item(s) at [\(mutations.map(String.init).joined(separator: ", "))]" as String,
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"- moved \(moves.count) item(s) at [\(moves.map(moveDescription).joined(separator: ", "))]" as String,
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] as [String]).joined(separator: "\n")
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}
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}

‎Sources/Delta.swift‎

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