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//===--- Join.swift - Protocol and Algorithm for concatenation ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// A sequence that presents the elements of a base sequence of sequences
/// concatenated using a given separator.
@frozen // lazy-performance
public struct JoinedSequence<Base: Sequence> where Base.Element: Sequence {
public typealias Element = Base.Element.Element
@usableFromInline // lazy-performance
internal var _base: Base
@usableFromInline // lazy-performance
internal var _separator: ContiguousArray<Element>
/// Creates an iterator that presents the elements of the sequences
/// traversed by `base`, concatenated using `separator`.
///
/// - Complexity: O(`separator.count`).
@inlinable // lazy-performance
public init<Separator: Sequence>(base: Base, separator: Separator)
where Separator.Element == Element {
self._base = base
self._separator = ContiguousArray(separator)
}
}
extension JoinedSequence: Sendable where Base: Sendable, Element: Sendable {}
extension JoinedSequence {
/// An iterator that presents the elements of the sequences traversed
/// by a base iterator, concatenated using a given separator.
@frozen // lazy-performance
public struct Iterator {
@frozen // lazy-performance
@usableFromInline // lazy-performance
internal enum _JoinIteratorState {
case start
case generatingElements
case generatingSeparator
case end
}
@usableFromInline // lazy-performance
internal var _base: Base.Iterator
@usableFromInline // lazy-performance
internal var _inner: Base.Element.Iterator?
@usableFromInline // lazy-performance
internal var _separatorData: ContiguousArray<Element>
@usableFromInline // lazy-performance
internal var _separator: ContiguousArray<Element>.Iterator?
@usableFromInline // lazy-performance
internal var _state: _JoinIteratorState = .start
/// Creates an iterator that presents the elements of `base` sequences
/// concatenated using `separator`.
///
/// - Complexity: O(`separator.count`).
@inlinable // lazy-performance
public init<Separator: Sequence>(base: Base.Iterator, separator: Separator)
where Separator.Element == Element {
self._base = base
self._separatorData = ContiguousArray(separator)
}
}
}
extension JoinedSequence.Iterator: Sendable
where Base.Iterator: Sendable,
Base.Element.Iterator: Sendable,
Element: Sendable {}
extension JoinedSequence.Iterator: IteratorProtocol {
public typealias Element = Base.Element.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 // lazy-performance
public mutating func next() -> Element? {
while true {
switch _state {
case .start:
if let nextSubSequence = _base.next() {
_inner = nextSubSequence.makeIterator()
_state = .generatingElements
} else {
_state = .end
return nil
}
case .generatingElements:
let result = _inner!.next()
if _fastPath(result != nil) {
return result
}
_inner = _base.next()?.makeIterator()
if _inner == nil {
_state = .end
return nil
}
if !_separatorData.isEmpty {
_separator = _separatorData.makeIterator()
_state = .generatingSeparator
}
case .generatingSeparator:
let result = _separator!.next()
if _fastPath(result != nil) {
return result
}
_state = .generatingElements
case .end:
return nil
}
}
}
}
extension JoinedSequence: Sequence {
/// Return an iterator over the elements of this sequence.
///
/// - Complexity: O(1).
@inlinable // lazy-performance
public __consuming func makeIterator() -> Iterator {
return Iterator(base: _base.makeIterator(), separator: _separator)
}
@inlinable // lazy-performance
public __consuming func _copyToContiguousArray() -> ContiguousArray<Element> {
var result = ContiguousArray<Element>()
let separatorSize = _separator.count
if separatorSize == 0 {
for x in _base {
result.append(contentsOf: x)
}
return result
}
var iter = _base.makeIterator()
if let first = iter.next() {
result.append(contentsOf: first)
while let next = iter.next() {
result.append(contentsOf: _separator)
result.append(contentsOf: next)
}
}
return result
}
}
extension Sequence where Element: Sequence {
/// Returns the concatenated elements of this sequence of sequences,
/// inserting the given separator between each element.
///
/// This example shows how an array of `[Int]` instances can be joined, using
/// another `[Int]` instance as the separator:
///
/// let nestedNumbers = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
/// let joined = nestedNumbers.joined(separator: [-1, -2])
/// print(Array(joined))
/// // Prints "[1, 2, 3, -1, -2, 4, 5, 6, -1, -2, 7, 8, 9]"
///
/// - Parameter separator: A sequence to insert between each of this
/// sequence's elements.
/// - Returns: The joined sequence of elements.
@inlinable // lazy-performance
public __consuming func joined<Separator: Sequence>(
separator: Separator
) -> JoinedSequence<Self>
where Separator.Element == Element.Element {
return JoinedSequence(base: self, separator: separator)
}
}
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