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99 lines
3.4 KiB
Swift
99 lines
3.4 KiB
Swift
//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See http://swift.org/LICENSE.txt for license information
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// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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/// A sequence of pairs built out of two underlying sequences, where
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/// the elements of the `i`th pair are the `i`th elements of each
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/// underlying sequence.
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public func zip<Sequence1 : Sequence, Sequence2 : Sequence>(
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sequence1: Sequence1, _ sequence2: Sequence2
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) -> Zip2Sequence<Sequence1, Sequence2> {
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return Zip2Sequence(_sequence1: sequence1, _sequence2: sequence2)
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}
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/// An iterator for `Zip2Sequence`.
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public struct Zip2Iterator<
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Iterator1 : IteratorProtocol, Iterator2 : IteratorProtocol
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> : IteratorProtocol {
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/// The type of element returned by `next()`.
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public typealias Element = (Iterator1.Element, Iterator2.Element)
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/// Construct around a pair of underlying iterators.
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internal init(_ iterator1: Iterator1, _ iterator2: Iterator2) {
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(_baseStream1, _baseStream2) = (iterator1, iterator2)
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}
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/// Advance to the next element and return it, or `nil` if no next
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/// element exists.
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///
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/// - Precondition: `next()` has not been applied to a copy of `self`
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/// since the copy was made, and no preceding call to `self.next()`
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/// has returned `nil`.
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public mutating func next() -> Element? {
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// The next() function needs to track if it has reached the end. If we
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// didn't, and the first sequence is longer than the second, then when we
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// have already exhausted the second sequence, on every subsequent call to
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// next() we would consume and discard one additional element from the
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// first sequence, even though next() had already returned nil.
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if _reachedEnd {
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return nil
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}
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guard let element1 = _baseStream1.next(), element2 = _baseStream2.next() else {
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_reachedEnd = true
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return nil
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}
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return (element1, element2)
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}
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internal var _baseStream1: Iterator1
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internal var _baseStream2: Iterator2
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internal var _reachedEnd: Bool = false
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}
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/// A sequence of pairs built out of two underlying sequences, where
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/// the elements of the `i`th pair are the `i`th elements of each
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/// underlying sequence.
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public struct Zip2Sequence<Sequence1 : Sequence, Sequence2 : Sequence>
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: Sequence {
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public typealias Stream1 = Sequence1.Iterator
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public typealias Stream2 = Sequence2.Iterator
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/// A type whose instances can produce the elements of this
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/// sequence, in order.
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public typealias Iterator = Zip2Iterator<Stream1, Stream2>
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@available(*, unavailable, renamed="Iterator")
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public typealias Generator = Iterator
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/// Construct an instance that makes pairs of elements from `sequence1` and
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/// `sequence2`.
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public // @testable
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init(_sequence1 sequence1: Sequence1, _sequence2 sequence2: Sequence2) {
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(_sequence1, _sequence2) = (sequence1, sequence2)
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}
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/// Returns an iterator over the elements of this sequence.
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///
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/// - Complexity: O(1).
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public func makeIterator() -> Iterator {
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return Iterator(
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_sequence1.makeIterator(),
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_sequence2.makeIterator())
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}
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internal let _sequence1: Sequence1
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internal let _sequence2: Sequence2
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}
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