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| /// The iterator for `LazyCycleSequence`. | |
| public struct LazyCycleIterator <BaseSequence: Sequence>: IteratorProtocol { | |
| public typealias Element = BaseSequence.Iterator.Element | |
| private let baseSequence: BaseSequence | |
| private var baseIterator: BaseSequence.Iterator | |
| internal init (_ baseSequence: BaseSequence) { | |
| self.baseSequence = baseSequence | |
| self.baseIterator = self.baseSequence.makeIterator() | |
| } | |
| public mutating func next () -> Element? { | |
| var next = self.baseIterator.next() | |
| if next == nil { | |
| self.baseIterator = self.baseSequence.makeIterator() | |
| next = self.baseIterator.next() | |
| } | |
| return next | |
| } | |
| } | |
| /// A lazily evaluated `Sequence` that infinitely repeats the elements of the base `Sequence`. | |
| /// | |
| /// - Attention: To create an instance of `LazyCycleSequence`, use the `cycle` property. | |
| public struct LazyCycleSequence <BaseSequence: Sequence>: LazySequenceProtocol { | |
| public typealias Iterator = LazyCycleIterator<BaseSequence> | |
| public typealias Element = Iterator.Element | |
| internal let baseSequence: BaseSequence | |
| internal init (_ baseSequence: BaseSequence) { | |
| self.baseSequence = baseSequence | |
| } | |
| public func makeIterator () -> Iterator { | |
| return Iterator(self.baseSequence) | |
| } | |
| } | |
| public extension LazyCycleSequence { | |
| /// Creates a lazily evaluated Sequence that infinitely repeats the elements of the base Sequence. | |
| /// | |
| /// print(Array([0, 1, 2].cycle.prefix(4))) | |
| /// // [0, 1, 2, 0] | |
| var cycle: LazyCycleSequence { | |
| return LazyCycleSequence(self.baseSequence) | |
| } | |
| } | |
| public extension LazySequence { | |
| /// Creates a lazily evaluated Sequence that infinitely repeats the elements of the base Sequence. | |
| /// | |
| /// print(Array([0, 1, 2].cycle.prefix(4))) | |
| /// // [0, 1, 2, 0] | |
| var cycle: LazyCycleSequence<Elements> { | |
| return LazyCycleSequence(self.elements) | |
| } | |
| } | |
| public extension Sequence { | |
| /// Creates a lazily evaluated Sequence that infinitely repeats the elements of the base Sequence. | |
| /// | |
| /// print(Array([0, 1, 2].cycle.prefix(4))) | |
| /// // [0, 1, 2, 0] | |
| var cycle: LazyCycleSequence<Self> { | |
| return LazyCycleSequence(self) | |
| } | |
| } | |
| import XCTest | |
| @testable import SequenceExtensions | |
| /// - Note: Since `cycle` is a newly defined property without any overloads we only check the type and value for the | |
| /// base `Sequence`. | |
| class CycleTests: XCTestCase { | |
| let baseSequence = sequence(first: 0, next: { | |
| if $0 < 2 { | |
| return $0 + 1 | |
| } | |
| return nil | |
| }) | |
| typealias BaseSequence = UnfoldSequence<Int, (Int?, Bool)> | |
| func testShouldReturnCorrectType () { | |
| XCTAssertTrue(type(of: self.baseSequence.cycle) == LazyCycleSequence<BaseSequence>.self) | |
| } | |
| func testShouldReturnCorrectValue () { | |
| XCTAssertEqual(Array(self.baseSequence.cycle.prefix(0)), []) | |
| XCTAssertEqual(Array(self.baseSequence.cycle.prefix(1)), [0]) | |
| XCTAssertEqual(Array(self.baseSequence.cycle.prefix(4)), [0, 1, 2, 0]) | |
| } | |
| } |
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