mirror of
https://github.com/apple/swift.git
synced 2025-12-21 12:14:44 +01:00
7bc7b1e22e
Now that we have removed overriding protocol requirements from witness tables, they no longer have any effect on the ABI. Replace the FIXME (ABI) comments with normal FIXMEs: there is no more ABI work to do here.
371 lines
15 KiB
Swift
371 lines
15 KiB
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
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// A collection that supports efficient random-access index traversal.
|
|
///
|
|
/// Random-access collections can move indices any distance and
|
|
/// measure the distance between indices in O(1) time. Therefore, the
|
|
/// fundamental difference between random-access and bidirectional collections
|
|
/// is that operations that depend on index movement or distance measurement
|
|
/// offer significantly improved efficiency. For example, a random-access
|
|
/// collection's `count` property is calculated in O(1) instead of requiring
|
|
/// iteration of an entire collection.
|
|
///
|
|
/// Conforming to the RandomAccessCollection Protocol
|
|
/// =================================================
|
|
///
|
|
/// The `RandomAccessCollection` protocol adds further constraints on the
|
|
/// associated `Indices` and `SubSequence` types, but otherwise imposes no
|
|
/// additional requirements over the `BidirectionalCollection` protocol.
|
|
/// However, in order to meet the complexity guarantees of a random-access
|
|
/// collection, either the index for your custom type must conform to the
|
|
/// `Strideable` protocol or you must implement the `index(_:offsetBy:)` and
|
|
/// `distance(from:to:)` methods with O(1) efficiency.
|
|
public protocol RandomAccessCollection: BidirectionalCollection
|
|
where SubSequence: RandomAccessCollection, Indices: RandomAccessCollection
|
|
{
|
|
// FIXME: Associated type inference requires these.
|
|
override associatedtype Element
|
|
override associatedtype Index
|
|
override associatedtype SubSequence
|
|
override associatedtype Indices
|
|
|
|
/// The indices that are valid for subscripting the collection, in ascending
|
|
/// order.
|
|
///
|
|
/// A collection's `indices` property can hold a strong reference to the
|
|
/// collection itself, causing the collection to be nonuniquely referenced.
|
|
/// If you mutate the collection while iterating over its indices, a strong
|
|
/// reference can result in an unexpected copy of the collection. To avoid
|
|
/// the unexpected copy, use the `index(after:)` method starting with
|
|
/// `startIndex` to produce indices instead.
|
|
///
|
|
/// var c = MyFancyCollection([10, 20, 30, 40, 50])
|
|
/// var i = c.startIndex
|
|
/// while i != c.endIndex {
|
|
/// c[i] /= 5
|
|
/// i = c.index(after: i)
|
|
/// }
|
|
/// // c == MyFancyCollection([2, 4, 6, 8, 10])
|
|
override var indices: Indices { get }
|
|
|
|
/// Accesses a contiguous subrange of the collection's elements.
|
|
///
|
|
/// The accessed slice uses the same indices for the same elements as the
|
|
/// original collection uses. Always use the slice's `startIndex` property
|
|
/// instead of assuming that its indices start at a particular value.
|
|
///
|
|
/// This example demonstrates getting a slice of an array of strings, finding
|
|
/// the index of one of the strings in the slice, and then using that index
|
|
/// in the original array.
|
|
///
|
|
/// let streets = ["Adams", "Bryant", "Channing", "Douglas", "Evarts"]
|
|
/// let streetsSlice = streets[2 ..< streets.endIndex]
|
|
/// print(streetsSlice)
|
|
/// // Prints "["Channing", "Douglas", "Evarts"]"
|
|
///
|
|
/// let index = streetsSlice.firstIndex(of: "Evarts") // 4
|
|
/// print(streets[index!])
|
|
/// // Prints "Evarts"
|
|
///
|
|
/// - Parameter bounds: A range of the collection's indices. The bounds of
|
|
/// the range must be valid indices of the collection.
|
|
///
|
|
/// - Complexity: O(1)
|
|
override subscript(bounds: Range<Index>) -> SubSequence { get }
|
|
|
|
// FIXME: Associated type inference requires these.
|
|
override subscript(position: Index) -> Element { get }
|
|
override var startIndex: Index { get }
|
|
override var endIndex: Index { get }
|
|
|
|
/// Returns the position immediately before the given index.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be greater than
|
|
/// `startIndex`.
|
|
/// - Returns: The index value immediately before `i`.
|
|
override func index(before i: Index) -> Index
|
|
|
|
/// Replaces the given index with its predecessor.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be greater than
|
|
/// `startIndex`.
|
|
override func formIndex(before i: inout Index)
|
|
|
|
/// Returns the position immediately after the given index.
|
|
///
|
|
/// The successor of an index must be well defined. For an index `i` into a
|
|
/// collection `c`, calling `c.index(after: i)` returns the same index every
|
|
/// time.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be less than
|
|
/// `endIndex`.
|
|
/// - Returns: The index value immediately after `i`.
|
|
override func index(after i: Index) -> Index
|
|
|
|
/// Replaces the given index with its successor.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be less than
|
|
/// `endIndex`.
|
|
override func formIndex(after i: inout Index)
|
|
|
|
/// Returns an index that is the specified distance from the given index.
|
|
///
|
|
/// The following example obtains an index advanced four positions from a
|
|
/// string's starting index and then prints the character at that position.
|
|
///
|
|
/// let s = "Swift"
|
|
/// let i = s.index(s.startIndex, offsetBy: 4)
|
|
/// print(s[i])
|
|
/// // Prints "t"
|
|
///
|
|
/// The value passed as `distance` must not offset `i` beyond the bounds of
|
|
/// the collection.
|
|
///
|
|
/// - Parameters:
|
|
/// - i: A valid index of the collection.
|
|
/// - distance: The distance to offset `i`. `distance` must not be negative
|
|
/// unless the collection conforms to the `BidirectionalCollection`
|
|
/// protocol.
|
|
/// - Returns: An index offset by `distance` from the index `i`. If
|
|
/// `distance` is positive, this is the same value as the result of
|
|
/// `distance` calls to `index(after:)`. If `distance` is negative, this
|
|
/// is the same value as the result of `abs(distance)` calls to
|
|
/// `index(before:)`.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@_nonoverride func index(_ i: Index, offsetBy distance: Int) -> Index
|
|
|
|
/// Returns an index that is the specified distance from the given index,
|
|
/// unless that distance is beyond a given limiting index.
|
|
///
|
|
/// The following example obtains an index advanced four positions from a
|
|
/// string's starting index and then prints the character at that position.
|
|
/// The operation doesn't require going beyond the limiting `s.endIndex`
|
|
/// value, so it succeeds.
|
|
///
|
|
/// let s = "Swift"
|
|
/// if let i = s.index(s.startIndex, offsetBy: 4, limitedBy: s.endIndex) {
|
|
/// print(s[i])
|
|
/// }
|
|
/// // Prints "t"
|
|
///
|
|
/// The next example attempts to retrieve an index six positions from
|
|
/// `s.startIndex` but fails, because that distance is beyond the index
|
|
/// passed as `limit`.
|
|
///
|
|
/// let j = s.index(s.startIndex, offsetBy: 6, limitedBy: s.endIndex)
|
|
/// print(j)
|
|
/// // Prints "nil"
|
|
///
|
|
/// The value passed as `distance` must not offset `i` beyond the bounds of
|
|
/// the collection, unless the index passed as `limit` prevents offsetting
|
|
/// beyond those bounds.
|
|
///
|
|
/// - Parameters:
|
|
/// - i: A valid index of the collection.
|
|
/// - distance: The distance to offset `i`. `distance` must not be negative
|
|
/// unless the collection conforms to the `BidirectionalCollection`
|
|
/// protocol.
|
|
/// - limit: A valid index of the collection to use as a limit. If
|
|
/// `distance > 0`, a limit that is less than `i` has no effect.
|
|
/// Likewise, if `distance < 0`, a limit that is greater than `i` has no
|
|
/// effect.
|
|
/// - Returns: An index offset by `distance` from the index `i`, unless that
|
|
/// index would be beyond `limit` in the direction of movement. In that
|
|
/// case, the method returns `nil`.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@_nonoverride func index(
|
|
_ i: Index, offsetBy distance: Int, limitedBy limit: Index
|
|
) -> Index?
|
|
|
|
/// Returns the distance between two indices.
|
|
///
|
|
/// Unless the collection conforms to the `BidirectionalCollection` protocol,
|
|
/// `start` must be less than or equal to `end`.
|
|
///
|
|
/// - Parameters:
|
|
/// - start: A valid index of the collection.
|
|
/// - end: Another valid index of the collection. If `end` is equal to
|
|
/// `start`, the result is zero.
|
|
/// - Returns: The distance between `start` and `end`. The result can be
|
|
/// negative only if the collection conforms to the
|
|
/// `BidirectionalCollection` protocol.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@_nonoverride func distance(from start: Index, to end: Index) -> Int
|
|
}
|
|
|
|
// TODO: swift-3-indexing-model - (By creating an ambiguity?), try to
|
|
// make sure RandomAccessCollection models implement
|
|
// index(_:offsetBy:) and distance(from:to:), or they will get the
|
|
// wrong complexity.
|
|
|
|
/// Default implementation for random access collections.
|
|
extension RandomAccessCollection {
|
|
/// Returns an index that is the specified distance from the given index,
|
|
/// unless that distance is beyond a given limiting index.
|
|
///
|
|
/// The following example obtains an index advanced four positions from an
|
|
/// array's starting index and then prints the element at that position. The
|
|
/// operation doesn't require going beyond the limiting `numbers.endIndex`
|
|
/// value, so it succeeds.
|
|
///
|
|
/// let numbers = [10, 20, 30, 40, 50]
|
|
/// let i = numbers.index(numbers.startIndex, offsetBy: 4)
|
|
/// print(numbers[i])
|
|
/// // Prints "50"
|
|
///
|
|
/// The next example attempts to retrieve an index ten positions from
|
|
/// `numbers.startIndex`, but fails, because that distance is beyond the
|
|
/// index passed as `limit`.
|
|
///
|
|
/// let j = numbers.index(numbers.startIndex,
|
|
/// offsetBy: 10,
|
|
/// limitedBy: numbers.endIndex)
|
|
/// print(j)
|
|
/// // Prints "nil"
|
|
///
|
|
/// The value passed as `distance` must not offset `i` beyond the bounds of
|
|
/// the collection, unless the index passed as `limit` prevents offsetting
|
|
/// beyond those bounds.
|
|
///
|
|
/// - Parameters:
|
|
/// - i: A valid index of the array.
|
|
/// - distance: The distance to offset `i`.
|
|
/// - limit: A valid index of the collection to use as a limit. If
|
|
/// `distance > 0`, `limit` should be greater than `i` to have any
|
|
/// effect. Likewise, if `distance < 0`, `limit` should be less than `i`
|
|
/// to have any effect.
|
|
/// - Returns: An index offset by `distance` from the index `i`, unless that
|
|
/// index would be beyond `limit` in the direction of movement. In that
|
|
/// case, the method returns `nil`.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@inlinable
|
|
public func index(
|
|
_ i: Index, offsetBy distance: Int, limitedBy limit: Index
|
|
) -> Index? {
|
|
// FIXME: swift-3-indexing-model: tests.
|
|
let l = self.distance(from: i, to: limit)
|
|
if distance > 0 ? l >= 0 && l < distance : l <= 0 && distance < l {
|
|
return nil
|
|
}
|
|
return index(i, offsetBy: distance)
|
|
}
|
|
}
|
|
|
|
// Provides an alternative default associated type witness for Indices
|
|
// for random access collections with strideable indices.
|
|
extension RandomAccessCollection where Index : Strideable, Index.Stride == Int {
|
|
@_implements(Collection, Indices)
|
|
public typealias _Default_Indices = Range<Index>
|
|
}
|
|
|
|
extension RandomAccessCollection
|
|
where Index : Strideable,
|
|
Index.Stride == Int,
|
|
Indices == Range<Index> {
|
|
|
|
/// The indices that are valid for subscripting the collection, in ascending
|
|
/// order.
|
|
@inlinable
|
|
public var indices: Range<Index> {
|
|
return startIndex..<endIndex
|
|
}
|
|
|
|
/// Returns the position immediately after the given index.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be less than
|
|
/// `endIndex`.
|
|
/// - Returns: The index value immediately after `i`.
|
|
@inlinable
|
|
public func index(after i: Index) -> Index {
|
|
// FIXME: swift-3-indexing-model: tests for the trap.
|
|
_failEarlyRangeCheck(
|
|
i, bounds: Range(uncheckedBounds: (startIndex, endIndex)))
|
|
return i.advanced(by: 1)
|
|
}
|
|
|
|
/// Returns the position immediately after the given index.
|
|
///
|
|
/// - Parameter i: A valid index of the collection. `i` must be greater than
|
|
/// `startIndex`.
|
|
/// - Returns: The index value immediately before `i`.
|
|
@inlinable // protocol-only
|
|
public func index(before i: Index) -> Index {
|
|
let result = i.advanced(by: -1)
|
|
// FIXME: swift-3-indexing-model: tests for the trap.
|
|
_failEarlyRangeCheck(
|
|
result, bounds: Range(uncheckedBounds: (startIndex, endIndex)))
|
|
return result
|
|
}
|
|
|
|
/// Returns an index that is the specified distance from the given index.
|
|
///
|
|
/// The following example obtains an index advanced four positions from an
|
|
/// array's starting index and then prints the element at that position.
|
|
///
|
|
/// let numbers = [10, 20, 30, 40, 50]
|
|
/// let i = numbers.index(numbers.startIndex, offsetBy: 4)
|
|
/// print(numbers[i])
|
|
/// // Prints "50"
|
|
///
|
|
/// The value passed as `distance` must not offset `i` beyond the bounds of
|
|
/// the collection.
|
|
///
|
|
/// - Parameters:
|
|
/// - i: A valid index of the collection.
|
|
/// - distance: The distance to offset `i`.
|
|
/// - Returns: An index offset by `distance` from the index `i`. If
|
|
/// `distance` is positive, this is the same value as the result of
|
|
/// `distance` calls to `index(after:)`. If `distance` is negative, this
|
|
/// is the same value as the result of `abs(distance)` calls to
|
|
/// `index(before:)`.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@inlinable
|
|
public func index(_ i: Index, offsetBy distance: Index.Stride) -> Index {
|
|
let result = i.advanced(by: distance)
|
|
// This range check is not precise, tighter bounds exist based on `n`.
|
|
// Unfortunately, we would need to perform index manipulation to
|
|
// compute those bounds, which is probably too slow in the general
|
|
// case.
|
|
// FIXME: swift-3-indexing-model: tests for the trap.
|
|
_failEarlyRangeCheck(
|
|
result, bounds: ClosedRange(uncheckedBounds: (startIndex, endIndex)))
|
|
return result
|
|
}
|
|
|
|
/// Returns the distance between two indices.
|
|
///
|
|
/// - Parameters:
|
|
/// - start: A valid index of the collection.
|
|
/// - end: Another valid index of the collection. If `end` is equal to
|
|
/// `start`, the result is zero.
|
|
/// - Returns: The distance between `start` and `end`.
|
|
///
|
|
/// - Complexity: O(1)
|
|
@inlinable
|
|
public func distance(from start: Index, to end: Index) -> Index.Stride {
|
|
// FIXME: swift-3-indexing-model: tests for traps.
|
|
_failEarlyRangeCheck(
|
|
start, bounds: ClosedRange(uncheckedBounds: (startIndex, endIndex)))
|
|
_failEarlyRangeCheck(
|
|
end, bounds: ClosedRange(uncheckedBounds: (startIndex, endIndex)))
|
|
return start.distance(to: end)
|
|
}
|
|
}
|
|
|
|
|