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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
/// Creates a sequence of pairs built out of two underlying sequences.
///
/// In the `Zip2Sequence` instance returned by this function, the elements of
/// the *i*th pair are the *i*th elements of each underlying sequence. The
/// following example uses the `zip(_:_:)` function to iterate over an array
/// of strings and a countable range at the same time:
///
/// let words = ["one", "two", "three", "four"]
/// let numbers = 1...4
///
/// for (word, number) in zip(words, numbers) {
/// print("\(word): \(number)")
/// }
/// // Prints "one: 1"
/// // Prints "two: 2
/// // Prints "three: 3"
/// // Prints "four: 4"
///
/// If the two sequences passed to `zip(_:_:)` are different lengths, the
/// resulting sequence is the same length as the shorter sequence. In this
/// example, the resulting array is the same length as `words`:
///
/// let naturalNumbers = 1...Int.max
/// let zipped = Array(zip(words, naturalNumbers))
/// // zipped == [("one", 1), ("two", 2), ("three", 3), ("four", 4)]
///
/// - Parameters:
/// - sequence1: The first sequence or collection to zip.
/// - sequence2: The second sequence or collection to zip.
/// - Returns: A sequence of tuple pairs, where the elements of each pair are
/// corresponding elements of `sequence1` and `sequence2`.
@inlinable // FIXME(sil-serialize-all)
public func zip<Sequence1, Sequence2>(
_ sequence1: Sequence1, _ sequence2: Sequence2
) -> Zip2Sequence<Sequence1, Sequence2> {
return Zip2Sequence(_sequence1: sequence1, _sequence2: sequence2)
}
/// A sequence of pairs built out of two underlying sequences.
///
/// In a `Zip2Sequence` instance, the elements of the *i*th pair are the *i*th
/// elements of each underlying sequence. To create a `Zip2Sequence` instance,
/// use the `zip(_:_:)` function.
///
/// The following example uses the `zip(_:_:)` function to iterate over an
/// array of strings and a countable range at the same time:
///
/// let words = ["one", "two", "three", "four"]
/// let numbers = 1...4
///
/// for (word, number) in zip(words, numbers) {
/// print("\(word): \(number)")
/// }
/// // Prints "one: 1"
/// // Prints "two: 2
/// // Prints "three: 3"
/// // Prints "four: 4"
@_fixed_layout // FIXME(sil-serialize-all)
public struct Zip2Sequence<Sequence1 : Sequence, Sequence2 : Sequence> {
@usableFromInline // FIXME(sil-serialize-all)
internal let _sequence1: Sequence1
@usableFromInline // FIXME(sil-serialize-all)
internal let _sequence2: Sequence2
/// Creates an instance that makes pairs of elements from `sequence1` and
/// `sequence2`.
@inlinable // FIXME(sil-serialize-all)
public // @testable
init(_sequence1 sequence1: Sequence1, _sequence2 sequence2: Sequence2) {
(_sequence1, _sequence2) = (sequence1, sequence2)
}
}
extension Zip2Sequence {
/// An iterator for `Zip2Sequence`.
@_fixed_layout // FIXME(sil-serialize-all)
public struct Iterator {
@usableFromInline // FIXME(sil-serialize-all)
internal var _baseStream1: Sequence1.Iterator
@usableFromInline // FIXME(sil-serialize-all)
internal var _baseStream2: Sequence2.Iterator
@usableFromInline // FIXME(sil-serialize-all)
internal var _reachedEnd: Bool = false
/// Creates an instance around a pair of underlying iterators.
@inlinable // FIXME(sil-serialize-all)
internal init(
_ iterator1: Sequence1.Iterator,
_ iterator2: Sequence2.Iterator
) {
(_baseStream1, _baseStream2) = (iterator1, iterator2)
}
}
}
extension Zip2Sequence.Iterator: IteratorProtocol {
/// The type of element returned by `next()`.
public typealias Element = (Sequence1.Element, Sequence2.Element)
/// Advances to the next element and returns it, or `nil` if no next element
/// exists.
///
/// Once `nil` has been returned, all subsequent calls return `nil`.
@inlinable // FIXME(sil-serialize-all)
public mutating func next() -> Element? {
// The next() function needs to track if it has reached the end. If we
// didn't, and the first sequence is longer than the second, then when we
// have already exhausted the second sequence, on every subsequent call to
// next() we would consume and discard one additional element from the
// first sequence, even though next() had already returned nil.
if _reachedEnd {
return nil
}
guard let element1 = _baseStream1.next(),
let element2 = _baseStream2.next() else {
_reachedEnd = true
return nil
}
return (element1, element2)
}
}
extension Zip2Sequence: Sequence {
public typealias Element = (Sequence1.Element, Sequence2.Element)
/// Returns an iterator over the elements of this sequence.
@inlinable // FIXME(sil-serialize-all)
public func makeIterator() -> Iterator {
return Iterator(
_sequence1.makeIterator(),
_sequence2.makeIterator())
}
}