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//===--- LazyCollection.swift ---------------------------------*- swift -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
public protocol LazyCollectionProtocol: Collection, LazySequenceProtocol
where Elements: Collection {}
extension LazyCollectionProtocol {
// Lazy things are already lazy
@inlinable // protocol-only
public var lazy: LazyCollection<Elements> {
return elements.lazy
}
}
extension LazyCollectionProtocol where Elements: LazyCollectionProtocol {
// Lazy things are already lazy
@inlinable // protocol-only
public var lazy: Elements {
return elements
}
}
/// A collection containing the same elements as a `Base` collection,
/// but on which some operations such as `map` and `filter` are
/// implemented lazily.
///
/// - See also: `LazySequenceProtocol`, `LazyCollection`
public typealias LazyCollection<T: Collection> = LazySequence<T>
extension LazyCollection: Collection {
/// A type that represents a valid position in the collection.
///
/// Valid indices consist of the position of every element and a
/// "past the end" position that's not valid for use as a subscript.
public typealias Index = Base.Index
public typealias Indices = Base.Indices
public typealias SubSequence = Slice<LazySequence>
/// The position of the first element in a non-empty collection.
///
/// In an empty collection, `startIndex == endIndex`.
@inlinable
public var startIndex: Index { return _base.startIndex }
/// The collection's "past the end" position---that is, the position one
/// greater than the last valid subscript argument.
///
/// `endIndex` is always reachable from `startIndex` by zero or more
/// applications of `index(after:)`.
@inlinable
public var endIndex: Index { return _base.endIndex }
@inlinable
public var indices: Indices { return _base.indices }
// TODO: swift-3-indexing-model - add docs
@inlinable
public func index(after i: Index) -> Index {
return _base.index(after: i)
}
/// Accesses the element at `position`.
///
/// - Precondition: `position` is a valid position in `self` and
/// `position != endIndex`.
@inlinable
public subscript(position: Index) -> Element {
return _base[position]
}
/// A Boolean value indicating whether the collection is empty.
@inlinable
public var isEmpty: Bool {
return _base.isEmpty
}
/// Returns the number of elements.
///
/// To check whether a collection is empty, use its `isEmpty` property
/// instead of comparing `count` to zero. Unless the collection guarantees
/// random-access performance, calculating `count` can be an O(*n*)
/// operation.
///
/// - Complexity: O(1) if `Self` conforms to `RandomAccessCollection`;
/// O(*n*) otherwise.
@inlinable
public var count: Int {
return _base.count
}
// The following requirement enables dispatching for firstIndex(of:) and
// lastIndex(of:) when the element type is Equatable.
/// Returns `Optional(Optional(index))` if an element was found;
/// `Optional(nil)` if the element doesn't exist in the collection;
/// `nil` if a search was not performed.
///
/// - Complexity: Better than O(*n*)
@inlinable
public func _customIndexOfEquatableElement(
_ element: Element
) -> Index?? {
return _base._customIndexOfEquatableElement(element)
}
/// Returns `Optional(Optional(index))` if an element was found;
/// `Optional(nil)` if the element doesn't exist in the collection;
/// `nil` if a search was not performed.
///
/// - Complexity: Better than O(*n*)
@inlinable
public func _customLastIndexOfEquatableElement(
_ element: Element
) -> Index?? {
return _base._customLastIndexOfEquatableElement(element)
}
// TODO: swift-3-indexing-model - add docs
@inlinable
public func index(_ i: Index, offsetBy n: Int) -> Index {
return _base.index(i, offsetBy: n)
}
// TODO: swift-3-indexing-model - add docs
@inlinable
public func index(
_ i: Index, offsetBy n: Int, limitedBy limit: Index
) -> Index? {
return _base.index(i, offsetBy: n, limitedBy: limit)
}
// TODO: swift-3-indexing-model - add docs
@inlinable
public func distance(from start: Index, to end: Index) -> Int {
return _base.distance(from:start, to: end)
}
}
extension LazyCollection: LazyCollectionProtocol { }
extension LazyCollection: BidirectionalCollection
where Base: BidirectionalCollection {
@inlinable
public func index(before i: Index) -> Index {
return _base.index(before: i)
}
}
extension LazyCollection: RandomAccessCollection
where Base: RandomAccessCollection {}
extension Slice: LazySequenceProtocol where Base: LazySequenceProtocol { }
extension ReversedCollection: LazySequenceProtocol where Base: LazySequenceProtocol { }
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