Skip to content
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

Jump to bottom

Add Stride for Collection #24

Merged
merged 11 commits into from
Dec 1, 2020
Merged

Add Stride for Collection #24

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
11 commits
Select commit Hold shift + click to select a range
17cb07e
Add Stride for Collection
ollieatkinson Oct 12, 2020
6df6133
Refactor to index(_:offsetBy:limitedBy:) and utilise the new test uti…
ollieatkinson Nov 1, 2020
4a194ca
remove redundant limit
ollieatkinson Nov 1, 2020
dcdef50
make base and stride internal
ollieatkinson Nov 2, 2020
6f7148d
Implementation of feedback from @timvermeulen
ollieatkinson Nov 6, 2020
28bbed8
Add implementation for Sequence iterator
ollieatkinson Nov 6, 2020
377bb72
small documentation tweek collection -> sequence
ollieatkinson Nov 6, 2020
92b2846
Add unbounded striding tests to check empty and sequence implementation
ollieatkinson Nov 6, 2020
0a6bcc3
compute the stride only when the next element is requested
ollieatkinson Nov 6, 2020
3669ff0
offsetBackward n is positive and remove init? from Index
ollieatkinson Nov 6, 2020
dfcc611
consistant negative stride
ollieatkinson Nov 6, 2020
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
Prev Previous commit
Next Next commit
Refactor to index(_:offsetBy:limitedBy:) and utilise the new test uti… 
…lities for validateIndexTraversals
  • Loading branch information
@ollieatkinson
ollieatkinson committed Nov 1, 2020
commit 6df6133ab7400b2b5a8c6fe40a94a4f74178cc43
60 changes: 35 additions & 25 deletions Sources/Algorithms/Stride.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,11 @@ extension Stride: Collection {
self.base = base
}

init?(_ base: Base.Index?) {
guard let base = base else { return nil }
self.base = base
}
ollieatkinson marked this conversation as resolved.
Show resolved Hide resolved

public static func < (lhs: Index, rhs: Index) -> Bool {
lhs.base < rhs.base
}
Expand All @@ -79,17 +84,34 @@ extension Stride: Collection {

public func index(after i: Index) -> Index {
precondition(i.base < base.endIndex, "Advancing past end index")
return base.index(i.base, offsetBy: stride, limitedBy: base.endIndex)
.map(Index.init) ?? endIndex
return index(i, offsetBy: 1, limitedBy: endIndex) ?? endIndex
}

public func index(
_ i: Index,
offsetBy distance: Int,
offsetBy n: Int,
limitedBy limit: Index
) -> Index? {
base.index(i.base, offsetBy: distance * stride, limitedBy: limit.base)
.map(Index.init)
guard n != 0 else { return i }
guard limit != i else { return nil }
switch (i, n) {
case (endIndex, ..<0):
let baseEnd = base.index(base.endIndex, offsetBy: -((base.count - 1) % stride + 1))
return Index(base.index(baseEnd, offsetBy: (n - n.signum()) * stride, limitedBy: limit.base))
case (_, 1...):
let max = limit < i ? endIndex.base : limit.base
let idx = base.index(i.base, offsetBy: n * stride, limitedBy: max)
if let idx = idx {
return idx > max ? endIndex : Index(idx)
}
guard i >= limit || limit == endIndex else {
return nil
}
let isToEnd = distance(from: i, to: endIndex) == n
return isToEnd ? endIndex : nil
case _:
return Index(base.index(i.base, offsetBy: n * stride, limitedBy: limit.base))
}
}

public var count: Int {
Expand All @@ -99,37 +121,25 @@ extension Stride: Collection {

public func distance(from start: Index, to end: Index) -> Int {
let distance = base.distance(from: start.base, to: end.base)
return distance / stride + (distance % stride > 0 ? 1 : 0)
return distance / stride + (abs(distance % stride) > 0 ? distance.signum() : 0)
ollieatkinson marked this conversation as resolved.
Show resolved Hide resolved
}

public func index(_ i: Index, offsetBy distance: Int) -> Index {
precondition(distance <= 0 || i.base < base.endIndex, "Advancing past end index")
precondition(distance >= 0 || i.base > base.startIndex, "Incrementing past start index")
return Index(base.index(i.base, offsetBy: distance * stride))
let limit = distance > 0 ? endIndex : startIndex
let idx = index(i, offsetBy: distance, limitedBy: limit)
precondition(idx != nil, "The distance \(distance) is not valid for this collection")
return idx!
}
}

extension Stride: BidirectionalCollection
where Base: RandomAccessCollection {

public func index(before i: Index) -> Index {
precondition(i.base > base.startIndex, "Incrementing past start index")
if i == endIndex {
let count = base.count
precondition(count > 0, "Can't move before the starting index")
return Index(
base.index(base.endIndex, offsetBy: -((count - 1) % stride + 1))
)
} else {
guard let step = base.index(
i.base,
offsetBy: -stride,
limitedBy: startIndex.base
) else {
fatalError("Incrementing past start index")
}
return Index(step)
}
return index(i, offsetBy: -1)
}
}

Expand Down
65 changes: 16 additions & 49 deletions Tests/SwiftAlgorithmsTests/StrideTests.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -89,59 +89,26 @@ final class StridingTests: XCTestCase {
}

func testIndexTraversals() {
let zero_to_one_hundered_range = 0...100
validateIndexTraversals(
(0...100).striding(by: 10)
// (0...100).striding(by: 11)
// (0...100).striding(by: 101)
zero_to_one_hundered_range.striding(by: 10),
zero_to_one_hundered_range.striding(by: 11),
zero_to_one_hundered_range.striding(by: 101)
)
let zero_to_one_hundered_array = zero_to_one_hundered_range.map{ $0 }
ollieatkinson marked this conversation as resolved.
Show resolved Hide resolved
validateIndexTraversals(
zero_to_one_hundered_array.striding(by: 10),
zero_to_one_hundered_array.striding(by: 11),
zero_to_one_hundered_array.striding(by: 101)
)
let string = "swift rocks".map(String.init)
validateIndexTraversals(
string.striding(by: 1),
string.striding(by: 2),
string.striding(by: 10)
)
}
ollieatkinson marked this conversation as resolved.
Show resolved Hide resolved

func testDistance() {

do {
let a = (0...100).striding(by: 11)
XCTAssertEqual(a.distance(from: a.startIndex, to: a.endIndex), a.count)
for (i, index) in a.indices.enumerated() {
XCTAssertEqual(a.distance(from: a.startIndex, to: index), i)
}

var i = a.startIndex
a.formIndex(&i, offsetBy: 3)
XCTAssertEqual(a.distance(from: a.startIndex, to: i), 3)
XCTAssertEqual(a[i], 33)
}

do {

let a = (0...100).striding(by: 10)
XCTAssertEqual(a.distance(from: a.startIndex, to: a.endIndex), a.count)

for (i, index) in a.indices.enumerated() {
XCTAssertEqual(a.distance(from: a.startIndex, to: index), i)
}

var i = a.startIndex
a.formIndex(&i, offsetBy: 3)
XCTAssertEqual(a.distance(from: a.startIndex, to: i), 3)
XCTAssertEqual(a[i], 30)
}

do {

let a = (0...100).striding(by: 101)
XCTAssertEqual(a.distance(from: a.startIndex, to: a.endIndex), a.count)

for (i, index) in a.indices.enumerated() {
XCTAssertEqual(a.distance(from: a.startIndex, to: index), i)
}

var i = a.startIndex
a.formIndex(&i, offsetBy: 1)
XCTAssertEqual(a.distance(from: a.startIndex, to: i), a.count)
XCTAssertEqual(i, a.endIndex)
// a[i] // == Fatal error: Index out of range
}
}

func testOffsetBy() {
let a = (0...100).striding(by: 22)
Expand Down