Skip to content

Update AdjacentPairs implementations and tests #139

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
May 5, 2021
Merged

Update AdjacentPairs implementations and tests #139

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
7be7d17
Update AdjacentPairs implementations and tests
natecook1000 May 5, 2021
f624ba9
Add conditional lazy conformances
natecook1000 May 5, 2021
9b173fa
Apply suggestions from code review
natecook1000 May 5, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
228 changes: 136 additions & 92 deletions Sources/Algorithms/AdjacentPairs.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,35 +18,35 @@ extension Sequence {
/// The following example uses the `adjacentPairs()` method to iterate over
/// adjacent pairs of integers:
///
/// for pair in (1...5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
/// for pair in (1...).prefix(5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
@inlinable
public func adjacentPairs() -> AdjacentPairsSequence<Self> {
AdjacentPairsSequence(base: self)
}
}

extension Collection {
/// A collection of adjacent pairs of elements built from an underlying collection.
/// A collection of adjacent pairs of elements built from an underlying
/// collection.
///
/// In an `AdjacentPairsCollection`, the elements of the *i*th pair are the *i*th
/// and *(i+1)*th elements of the underlying sequence. The following example
/// uses the `adjacentPairs()` method to iterate over adjacent pairs of
/// integers:
/// ```
/// for pair in (1...5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
/// ```
/// In an `AdjacentPairsCollection`, the elements of the *i*th pair are the
/// *i*th and *(i+1)*th elements of the underlying sequence. The following
/// example uses the `adjacentPairs()` method to iterate over adjacent pairs
/// of integers:
///
/// for pair in (1...5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
@inlinable
public func adjacentPairs() -> AdjacentPairsCollection<Self> {
AdjacentPairsCollection(base: self)
Expand All @@ -55,19 +55,8 @@ extension Collection {

/// A sequence of adjacent pairs of elements built from an underlying sequence.
///
/// In an `AdjacentPairsSequence`, the elements of the *i*th pair are the *i*th
/// and *(i+1)*th elements of the underlying sequence. The following example
/// uses the `adjacentPairs()` method to iterate over adjacent pairs of
/// integers:
/// ```
/// for pair in (1...5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
/// ```
/// Use the `adjacentPairs()` method on a sequence to create an
/// `AdjacentPairsSequence` instance.
public struct AdjacentPairsSequence<Base: Sequence> {
@usableFromInline
internal let base: Base
Expand All @@ -80,6 +69,7 @@ public struct AdjacentPairsSequence<Base: Sequence> {
}

extension AdjacentPairsSequence {
/// The iterator for an `AdjacentPairsSequence` or `AdjacentPairsCollection`.
public struct Iterator {
@usableFromInline
internal var base: Base.Iterator
Expand Down Expand Up @@ -124,21 +114,14 @@ extension AdjacentPairsSequence: Sequence {
}
}

/// A collection of adjacent pairs of elements built from an underlying collection.
extension AdjacentPairsSequence: LazySequenceProtocol
where Base: LazySequenceProtocol {}

/// A collection of adjacent pairs of elements built from an underlying
/// collection.
///
/// In an `AdjacentPairsCollection`, the elements of the *i*th pair are the *i*th
/// and *(i+1)*th elements of the underlying sequence. The following example
/// uses the `adjacentPairs()` method to iterate over adjacent pairs of
/// integers:
/// ```
/// for pair in (1...5).adjacentPairs() {
/// print(pair)
/// }
/// // Prints "(1, 2)"
/// // Prints "(2, 3)"
/// // Prints "(3, 4)"
/// // Prints "(4, 5)"
/// ```
/// Use the `adjacentPairs()` method on a collection to create an
/// `AdjacentPairsCollection` instance.
public struct AdjacentPairsCollection<Base: Collection> {
@usableFromInline
internal let base: Base
Expand All @@ -148,13 +131,25 @@ public struct AdjacentPairsCollection<Base: Collection> {
@inlinable
internal init(base: Base) {
self.base = base

// Lazily build the end index, since we can't use the instance
// property pre-initialization
var endIndex: Index {
Index(first: base.endIndex, second: base.endIndex)
}

// Precompute `startIndex` to ensure O(1) behavior,
// avoiding indexing past `endIndex`
let start = base.startIndex
let end = base.endIndex
let second = start == end ? start : base.index(after: start)
self.startIndex = Index(first: start, second: second)
// Precompute `startIndex` to ensure O(1) behavior.
guard !base.isEmpty else {
self.startIndex = endIndex
return
}

// If there's only one element (i.e. the second index of base == endIndex)
// then this collection should be empty.
let secondIndex = base.index(after: base.startIndex)
self.startIndex = secondIndex == base.endIndex
? endIndex
: Index(first: base.startIndex, second: secondIndex)
}
}

Expand All @@ -168,6 +163,7 @@ extension AdjacentPairsCollection {
}

extension AdjacentPairsCollection {
/// A position in an `AdjacentPairsCollection`.
public struct Index: Comparable {
@usableFromInline
internal var first: Base.Index
Expand All @@ -181,22 +177,22 @@ extension AdjacentPairsCollection {
self.second = second
}

@inlinable
public static func ==(lhs: Index, rhs: Index) -> Bool {
lhs.first == rhs.first
}

@inlinable
public static func < (lhs: Index, rhs: Index) -> Bool {
(lhs.first, lhs.second) < (rhs.first, rhs.second)
lhs.first < rhs.first
}
}
}

extension AdjacentPairsCollection: Collection {
@inlinable
public var endIndex: Index {
switch base.endIndex {
case startIndex.first, startIndex.second:
return startIndex
case let end:
return Index(first: end, second: end)
}
Index(first: base.endIndex, second: base.endIndex)
}

@inlinable
Expand All @@ -206,6 +202,7 @@ extension AdjacentPairsCollection: Collection {

@inlinable
public func index(after i: Index) -> Index {
precondition(i != endIndex, "Can't advance beyond endIndex")
let next = base.index(after: i.second)
return next == base.endIndex
? endIndex
Expand All @@ -214,38 +211,74 @@ extension AdjacentPairsCollection: Collection {

@inlinable
public func index(_ i: Index, offsetBy distance: Int) -> Index {
if distance == 0 {
return i
} else if distance > 0 {
let firstOffsetIndex = base.index(i.first, offsetBy: distance)
let secondOffsetIndex = base.index(after: firstOffsetIndex)
return secondOffsetIndex == base.endIndex
? endIndex
: Index(first: firstOffsetIndex, second: secondOffsetIndex)
guard distance != 0 else { return i }

guard let result = distance > 0
? offsetForward(i, by: distance, limitedBy: endIndex)
: offsetBackward(i, by: -distance, limitedBy: startIndex)
else { fatalError("Index out of bounds") }
return result
}

@inlinable
public func index(
_ i: Index, offsetBy distance: Int, limitedBy limit: Index
) -> Index? {
guard distance != 0 else { return i }
guard limit != i else { return nil }

if distance > 0 {
let limit = limit > i ? limit : endIndex
return offsetForward(i, by: distance, limitedBy: limit)
} else {
return i == endIndex
? Index(first: base.index(i.first, offsetBy: distance - 1),
second: base.index(i.first, offsetBy: distance))
: Index(first: base.index(i.first, offsetBy: distance),
second: i.first)
let limit = limit < i ? limit : startIndex
return offsetBackward(i, by: -distance, limitedBy: limit)
}
}

@inlinable
internal func offsetForward(
_ i: Index, by distance: Int, limitedBy limit: Index
) -> Index? {
assert(distance > 0)
assert(limit > i)

guard let newFirst = base.index(i.second, offsetBy: distance - 1, limitedBy: limit.first),
newFirst != base.endIndex
else { return nil }
let newSecond = base.index(after: newFirst)

precondition(newSecond <= base.endIndex, "Can't advance beyond endIndex")
return newSecond == base.endIndex
? endIndex
: Index(first: newFirst, second: newSecond)
}

@inlinable
internal func offsetBackward(
_ i: Index, by distance: Int, limitedBy limit: Index
) -> Index? {
assert(distance > 0)
assert(limit < i)

let offset = i == endIndex ? 0 : 1
guard let newSecond = base.index(
i.first,
offsetBy: -(distance - offset),
limitedBy: limit.second)
else { return nil }
let newFirst = base.index(newSecond, offsetBy: -1)
precondition(newFirst >= base.startIndex, "Can't move before startIndex")
return Index(first: newFirst, second: newSecond)
}

@inlinable
public func distance(from start: Index, to end: Index) -> Int {
let offset: Int
switch (start.first, end.first) {
case (base.endIndex, base.endIndex):
return 0
case (base.endIndex, _):
offset = +1
case (_, base.endIndex):
offset = -1
default:
offset = 0
}

return base.distance(from: start.first, to: end.first) + offset
// While there's a 2-step gap between the `first` base index values in
// `endIndex` and the penultimate index of this collection, the `second`
// base index values are consistently one step apart throughout the
// entire collection.
base.distance(from: start.second, to: end.second)
}

@inlinable
Expand All @@ -259,13 +292,24 @@ extension AdjacentPairsCollection: BidirectionalCollection
{
@inlinable
public func index(before i: Index) -> Index {
i == endIndex
? Index(first: base.index(i.first, offsetBy: -2),
second: base.index(before: i.first))
: Index(first: base.index(before: i.first),
second: i.first)
precondition(i != startIndex, "Can't offset before startIndex")
let second = i == endIndex
? base.index(before: base.endIndex)
: i.first
let first = base.index(before: second)
return Index(first: first, second: second)
}
}

extension AdjacentPairsCollection: RandomAccessCollection
where Base: RandomAccessCollection {}

extension AdjacentPairsCollection: LazySequenceProtocol, LazyCollectionProtocol
where Base: LazyCollectionProtocol {}

extension AdjacentPairsCollection.Index: Hashable where Base.Index: Hashable {
@inlinable
public func hash(into hasher: inout Hasher) {
hasher.combine(first)
}
}
Loading