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Add labels to the tuples produced by chunked(on:) #259

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Add labels to the tuples produced by chunked(on:) #259

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5 changes: 3 additions & 2 deletions Sources/Algorithms/Chunked.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,7 @@ public struct ChunkedOnCollection<Base: Collection, Subject: Equatable> {

extension ChunkedOnCollection: Collection {
public typealias Index = ChunkedByCollection<Base, Subject>.Index
public typealias Element = (subject: Subject, chunk: Base.SubSequence)
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cf. IndexedCollection:

swift-algorithms/Sources/Algorithms/Indexed.swift

Lines 25 to 27 in 0b70cac

extension IndexedCollection: Collection {
/// The element type for an `IndexedCollection` collection.
public typealias Element = (index: Base.Index, element: Base.Element)


@inlinable
public var startIndex: Index {
Expand All @@ -174,7 +175,7 @@ extension ChunkedOnCollection: Collection {
}

@inlinable
public subscript(position: Index) -> (Subject, Base.SubSequence) {
public subscript(position: Index) -> Element {
let subsequence = chunked[position]
// swift-format-ignore: NeverForceUnwrap
// Chunks are never empty, so `.first!` is safe.
Expand Down Expand Up @@ -509,7 +510,7 @@ extension Collection {
@inlinable
public func chunked<Subject: Equatable>(
on projection: (Element) throws -> Subject
) rethrows -> [(Subject, SubSequence)] {
) rethrows -> [ChunkedOnCollection<Self, Subject>.Element] {
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@cweider cweider Aug 8, 2025 •
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The implementation below sidesteps ChunkedOnCollection, but aliasing seems sensible given Array-ness is the only material difference between this and the LazySequenceProtocol function.

guard !isEmpty else { return [] }
var result: [(Subject, SubSequence)] = []

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10 changes: 10 additions & 0 deletions Tests/SwiftAlgorithmsTests/ChunkedTests.swift
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Expand Up @@ -71,6 +71,16 @@ final class ChunkedTests: XCTestCase {
IndexValidator().validate(lazyChunks)
}

func testChunkedOnLabels() {
let arrayChunks: Array = fruits.chunked(on: { $0.first })
XCTAssert(arrayChunks.first!.0 == arrayChunks.first!.subject)
XCTAssert(arrayChunks.first!.1 == arrayChunks.first!.chunk)

let lazyChunks = fruits.lazy.chunked(on: { $0.first })
XCTAssert(lazyChunks.first!.0 == lazyChunks.first!.subject)
XCTAssert(lazyChunks.first!.1 == lazyChunks.first!.chunk)
}
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@cweider cweider Aug 8, 2025 •
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Test is a bit artificial – correctness is known statically. The best justification is that inhibits subsequent change to the labels. I welcome your thoughts here.


func testChunkedBy() {
validateFruitChunks(fruits.chunked(by: { $0.first == $1.first }))

Expand Down