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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2022 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
//
//===----------------------------------------------------------------------===//
/// Use this protocol to conform custom C++ sequence types to Swift's `Sequence`
/// protocol like this:
///
/// extension MyCxxSequenceType : CxxSequence {}
///
/// This requires the C++ sequence type to define const methods `begin()` and
/// `end()` which return input iterators into the C++ sequence. The iterator
/// types must conform to `UnsafeCxxInputIterator`.
public protocol CxxSequence<Element>: CxxConvertibleToCollection, Sequence {
override associatedtype Element
override associatedtype RawIterator: UnsafeCxxInputIterator
where RawIterator.Pointee == Element
override associatedtype Iterator = CxxIterator<Self>
// `begin()` and `end()` have to be mutating, otherwise calling
// `self.sequence.begin()` will copy `self.sequence` into a temporary value,
// and the result will be dangling. This does not mean that the implementing
// methods _have_ to be mutating.
/// Do not implement this function manually in Swift.
mutating func __beginUnsafe() -> RawIterator
/// Do not implement this function manually in Swift.
mutating func __endUnsafe() -> RawIterator
}
/// Prevents a C++ sequence from being copied or moved implicitly. Makes sure
/// that raw C++ iterators pointing into the sequence are not invalidated.
@usableFromInline
internal final class CxxSequenceBox<T> where T: CxxSequence {
@usableFromInline
internal var sequence: T
@usableFromInline
internal init(_ sequence: __shared T) {
self.sequence = sequence
}
}
@frozen
public struct CxxIterator<T>: IteratorProtocol where T: CxxSequence {
public typealias Element = T.RawIterator.Pointee
@usableFromInline
internal let sequence: CxxSequenceBox<T>
@usableFromInline
internal var rawIterator: T.RawIterator
@usableFromInline
internal let endIterator: T.RawIterator
@inlinable
public init(sequence: __shared T) {
self.sequence = CxxSequenceBox<T>(sequence)
self.rawIterator = self.sequence.sequence.__beginUnsafe()
self.endIterator = self.sequence.sequence.__endUnsafe()
}
@inlinable
public mutating func next() -> Element? {
if self.rawIterator == self.endIterator {
return nil
}
let object = self.rawIterator.pointee
self.rawIterator = self.rawIterator.successor()
return object
}
}
extension CxxSequence {
/// Returns an iterator over the elements of this C++ container.
///
/// - Complexity: O(*n*), where *n* is the number of elements in the C++
/// container when each element is copied in O(1). Note that this might not
/// be true for certain C++ types, e.g. those with a custom copy
/// constructor that performs additional logic.
@inlinable
public func makeIterator() -> CxxIterator<Self> {
return CxxIterator(sequence: self)
}
}
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