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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 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
//
//===----------------------------------------------------------------------===//
/// An iterator that persistently remembers the most recent element returned by `next()`.
struct RememberingIterator<Base: IteratorProtocol>: IteratorProtocol {
/// The wrapped iterator.
private var base: Base
/// The element most recently returned by the `next()` method.
///
/// This value will always remain equal to the last non-nil element returned by `next()`, even if
/// multiple calls to `next()` are made that return nil after the iterator has been exhausted.
/// Therefore, this property only evaluates to `nil` if the iterator had no elements in the first
/// place.
private(set) var latestElement: Base.Element?
/// Creates a new remembering iterator that wraps the specified iterator.
init(_ base: Base) {
self.base = base
self.latestElement = nil
}
mutating func next() -> Base.Element? {
let element = base.next()
if element != nil {
latestElement = element
}
return element
}
}
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