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512 lines
17 KiB
Swift
512 lines
17 KiB
Swift
//===--- StringUTF16.swift ------------------------------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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// FIXME(ABI)#71 : The UTF-16 string view should have a custom iterator type to
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// allow performance optimizations of linear traversals.
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extension String {
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/// A view of a string's contents as a collection of UTF-16 code units.
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///
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/// You can access a string's view of UTF-16 code units by using its `utf16`
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/// property. A string's UTF-16 view encodes the string's Unicode scalar
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/// values as 16-bit integers.
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///
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/// let flowers = "Flowers 💐"
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/// for v in flowers.utf16 {
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/// print(v)
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/// }
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/// // 70
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/// // 108
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/// // 111
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/// // 119
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/// // 101
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/// // 114
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/// // 115
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/// // 32
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/// // 55357
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/// // 56464
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///
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/// Unicode scalar values that make up a string's contents can be up to 21
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/// bits long. The longer scalar values may need two `UInt16` values for
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/// storage. Those "pairs" of code units are called *surrogate pairs*.
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///
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/// let flowermoji = "💐"
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/// for v in flowermoji.unicodeScalars {
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/// print(v, v.value)
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/// }
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/// // 💐 128144
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///
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/// for v in flowermoji.utf16 {
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/// print(v)
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/// }
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/// // 55357
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/// // 56464
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///
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/// To convert a `String.UTF16View` instance back into a string, use the
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/// `String` type's `init(_:)` initializer.
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///
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/// let favemoji = "My favorite emoji is 🎉"
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/// if let i = favemoji.utf16.index(where: { $0 >= 128 }) {
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/// let asciiPrefix = String(favemoji.utf16[..<i])
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/// print(asciiPrefix)
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/// }
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/// // Prints "My favorite emoji is "
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///
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/// UTF16View Elements Match NSString Characters
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/// ============================================
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///
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/// The UTF-16 code units of a string's `utf16` view match the elements
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/// accessed through indexed `NSString` APIs.
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///
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/// print(flowers.utf16.count)
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/// // Prints "10"
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///
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/// let nsflowers = flowers as NSString
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/// print(nsflowers.length)
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/// // Prints "10"
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///
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/// Unlike `NSString`, however, `String.UTF16View` does not use integer
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/// indices. If you need to access a specific position in a UTF-16 view, use
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/// Swift's index manipulation methods. The following example accesses the
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/// fourth code unit in both the `flowers` and `nsflowers` strings:
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///
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/// print(nsflowers.character(at: 3))
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/// // Prints "119"
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///
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/// let i = flowers.utf16.index(flowers.utf16.startIndex, offsetBy: 3)
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/// print(flowers.utf16[i])
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/// // Prints "119"
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///
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/// Although the Swift overlay updates many Objective-C methods to return
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/// native Swift indices and index ranges, some still return instances of
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/// `NSRange`. To convert an `NSRange` instance to a range of
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/// `String.UTF16View.Index`, follow these steps:
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///
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/// 1. Use the `NSRange` type's `toRange` method to convert the instance to
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/// an optional range of `Int` values.
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/// 2. Use your string's `utf16` view's index manipulation methods to convert
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/// the integer bounds to `String.UTF16View.Index` values.
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/// 3. Create a new `Range` instance from the new index values.
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///
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/// Here's an implementation of those steps, showing how to retrieve a
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/// substring described by an `NSRange` instance from the middle of a
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/// string.
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///
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/// let snowy = "❄️ Let it snow! ☃️"
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/// let nsrange = NSRange(location: 3, length: 12)
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/// if let r = nsrange.toRange() {
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/// let start = snowy.utf16.index(snowy.utf16.startIndex, offsetBy: r.lowerBound)
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/// let end = snowy.utf16.index(snowy.utf16.startIndex, offsetBy: r.upperBound)
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/// let substringRange = start..<end
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/// print(snowy.utf16[substringRange])
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/// }
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/// // Prints "Let it snow!"
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public struct UTF16View
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: BidirectionalCollection,
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CustomStringConvertible,
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CustomDebugStringConvertible {
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public typealias Index = String.Index
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public typealias IndexDistance = Int
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/// The position of the first code unit if the `String` is
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/// nonempty; identical to `endIndex` otherwise.
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public var startIndex: Index {
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return Index(encodedOffset: _offset)
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}
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/// The "past the end" position---that is, the position one greater than
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/// the last valid subscript argument.
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///
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/// In an empty UTF-16 view, `endIndex` is equal to `startIndex`.
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public var endIndex: Index {
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return Index(encodedOffset: _offset + _length)
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}
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public struct Indices {
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internal var _elements: String.UTF16View
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internal var _startIndex: Index
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internal var _endIndex: Index
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}
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public var indices: Indices {
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return Indices(
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_elements: self, startIndex: startIndex, endIndex: endIndex)
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}
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// TODO: swift-3-indexing-model - add docs
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public func index(after i: Index) -> Index {
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// FIXME: swift-3-indexing-model: range check i?
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return Index(encodedOffset: _unsafePlus(i.encodedOffset, 1))
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}
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// TODO: swift-3-indexing-model - add docs
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public func index(before i: Index) -> Index {
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// FIXME: swift-3-indexing-model: range check i?
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return Index(encodedOffset: _unsafeMinus(i.encodedOffset, 1))
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}
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// TODO: swift-3-indexing-model - add docs
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public func index(_ i: Index, offsetBy n: IndexDistance) -> Index {
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// FIXME: swift-3-indexing-model: range check i?
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return Index(encodedOffset: i.encodedOffset.advanced(by: n))
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}
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// TODO: swift-3-indexing-model - add docs
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public func index(
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_ i: Index, offsetBy n: IndexDistance, limitedBy limit: Index
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) -> Index? {
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// FIXME: swift-3-indexing-model: range check i?
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let d = i.encodedOffset.distance(to: limit.encodedOffset)
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if (d > 0) ? (d < n) : (d > n) {
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return nil
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}
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return Index(encodedOffset: i.encodedOffset.advanced(by: n))
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}
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// TODO: swift-3-indexing-model - add docs
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public func distance(from start: Index, to end: Index) -> IndexDistance {
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// FIXME: swift-3-indexing-model: range check start and end?
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return start.encodedOffset.distance(to: end.encodedOffset)
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}
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func _internalIndex(at i: Int) -> Int {
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return _core.startIndex + i
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}
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/// Accesses the code unit at the given position.
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///
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/// The following example uses the subscript to print the value of a
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/// string's first UTF-16 code unit.
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///
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/// let greeting = "Hello, friend!"
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/// let i = greeting.utf16.startIndex
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/// print("First character's UTF-16 code unit: \(greeting.utf16[i])")
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/// // Prints "First character's UTF-16 code unit: 72"
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///
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/// - Parameter position: A valid index of the view. `position` must be
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/// less than the view's end index.
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public subscript(i: Index) -> UTF16.CodeUnit {
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_precondition(i >= startIndex && i < endIndex,
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"out-of-range access on a UTF16View")
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let index = _internalIndex(at: i.encodedOffset)
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let u = _core[index]
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if _fastPath((u &>> 11) != 0b1101_1) {
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// Neither high-surrogate, nor low-surrogate -- well-formed sequence
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// of 1 code unit.
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return u
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}
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if (u &>> 10) == 0b1101_10 {
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// `u` is a high-surrogate. Sequence is well-formed if it
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// is followed by a low-surrogate.
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if _fastPath(
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index + 1 < _core.count &&
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(_core[index + 1] &>> 10) == 0b1101_11) {
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return u
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}
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return 0xfffd
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}
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// `u` is a low-surrogate. Sequence is well-formed if
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// previous code unit is a high-surrogate.
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if _fastPath(index != 0 && (_core[index - 1] &>> 10) == 0b1101_10) {
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return u
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}
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return 0xfffd
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}
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#if _runtime(_ObjC)
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// These may become less important once <rdar://problem/19255291> is addressed.
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@available(
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*, unavailable,
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message: "Indexing a String's UTF16View requires a String.UTF16View.Index, which can be constructed from Int when Foundation is imported")
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public subscript(i: Int) -> UTF16.CodeUnit {
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Builtin.unreachable()
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}
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@available(
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*, unavailable,
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message: "Slicing a String's UTF16View requires a Range<String.UTF16View.Index>, String.UTF16View.Index can be constructed from Int when Foundation is imported")
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public subscript(bounds: Range<Int>) -> UTF16View {
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Builtin.unreachable()
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}
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#endif
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/// Accesses the contiguous subrange of elements enclosed by the specified
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/// range.
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///
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/// - Complexity: O(*n*) if the underlying string is bridged from
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/// Objective-C, where *n* is the length of the string; otherwise, O(1).
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public subscript(bounds: Range<Index>) -> UTF16View {
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return UTF16View(
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_core,
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offset: _internalIndex(at: bounds.lowerBound.encodedOffset),
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length: bounds.upperBound.encodedOffset - bounds.lowerBound.encodedOffset)
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}
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internal init(_ _core: _StringCore) {
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self.init(_core, offset: 0, length: _core.count)
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}
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internal init(_ _core: _StringCore, offset: Int, length: Int) {
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self._offset = offset
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self._length = length
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self._core = _core
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}
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public var description: String {
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let start = _internalIndex(at: _offset)
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let end = _internalIndex(at: _offset + _length)
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return String(_core[start..<end])
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}
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public var debugDescription: String {
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return "StringUTF16(\(self.description.debugDescription))"
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}
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internal var _offset: Int
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internal var _length: Int
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internal let _core: _StringCore
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}
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/// A UTF-16 encoding of `self`.
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public var utf16: UTF16View {
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get {
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return UTF16View(_core)
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}
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set {
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self = String(describing: newValue)
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}
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}
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/// Creates a string corresponding to the given sequence of UTF-16 code units.
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///
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/// If `utf16` contains unpaired UTF-16 surrogates, the result is `nil`.
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///
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/// You can use this initializer to create a new string from a slice of
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/// another string's `utf16` view.
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///
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/// let picnicGuest = "Deserving porcupine"
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/// if let i = picnicGuest.utf16.index(of: 32) {
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/// let adjective = String(picnicGuest.utf16[..<i])
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/// print(adjective)
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/// }
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/// // Prints "Optional(Deserving)"
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///
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/// The `adjective` constant is created by calling this initializer with a
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/// slice of the `picnicGuest.utf16` view.
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///
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/// - Parameter utf16: A UTF-16 code sequence.
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public init?(_ utf16: UTF16View) {
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let wholeString = String(utf16._core)
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guard
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let start = UTF16Index(encodedOffset: utf16._offset)
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.samePosition(in: wholeString),
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let end = UTF16Index(encodedOffset: utf16._offset + utf16._length)
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.samePosition(in: wholeString)
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else
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{
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return nil
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}
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self = String(wholeString[start..<end])
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}
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/// The index type for subscripting a string's `utf16` view.
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public typealias UTF16Index = UTF16View.Index
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}
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extension String.UTF16View : _SwiftStringView {
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var _ephemeralContent : String { return _persistentContent }
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var _persistentContent : String { return String(self._core) }
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}
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// Index conversions
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extension String.UTF16View.Index {
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/// Creates an index in the given UTF-16 view that corresponds exactly to the
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/// specified string position.
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///
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/// The following example finds the position of a space in a string and then
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/// converts that position to an index in the string's `utf16` view.
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///
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/// let cafe = "Café 🍵"
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///
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/// let stringIndex = cafe.index(of: "é")!
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/// let utf16Index = String.UTF16View.Index(stringIndex, within: cafe.utf16)
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///
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/// print(cafe.utf16[...utf16Index])
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/// // Prints "Café"
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///
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/// - Parameters:
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/// - sourcePosition: A position in a string or one of its views
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/// - target: The `UTF16View` in which to find the new position.
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public init?(
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_ sourcePosition: String.Index, within target: String.UTF16View
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) {
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guard sourcePosition._transcodedOffset == 0 else { return nil }
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self.init(encodedOffset: sourcePosition.encodedOffset)
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}
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/// Returns the position in the given view of Unicode scalars that
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/// corresponds exactly to this index.
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///
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/// This index must be a valid index of `String(unicodeScalars).utf16`.
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///
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/// This example first finds the position of a space (UTF-16 code point `32`)
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/// in a string's `utf16` view and then uses this method to find the same
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/// position in the string's `unicodeScalars` view.
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///
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/// let cafe = "Café 🍵"
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/// let i = cafe.utf16.index(of: 32)!
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/// let j = i.samePosition(in: cafe.unicodeScalars)!
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/// print(cafe.unicodeScalars[..<j])
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/// // Prints "Café"
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///
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/// - Parameter unicodeScalars: The view to use for the index conversion.
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/// - Returns: The position in `unicodeScalars` that corresponds exactly to
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/// this index. If this index does not have an exact corresponding
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/// position in `unicodeScalars`, this method returns `nil`. For example,
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/// an attempt to convert the position of a UTF-16 trailing surrogate
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/// returns `nil`.
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public func samePosition(
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in unicodeScalars: String.UnicodeScalarView
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) -> String.UnicodeScalarIndex? {
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return String.UnicodeScalarIndex(self, within: unicodeScalars)
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}
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}
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// Reflection
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extension String.UTF16View : CustomReflectable {
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/// Returns a mirror that reflects the UTF-16 view of a string.
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public var customMirror: Mirror {
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return Mirror(self, unlabeledChildren: self)
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}
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}
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extension String.UTF16View : CustomPlaygroundQuickLookable {
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public var customPlaygroundQuickLook: PlaygroundQuickLook {
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return .text(description)
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}
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}
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extension String.UTF16View.Indices : BidirectionalCollection {
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public typealias Index = String.UTF16View.Index
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public typealias IndexDistance = String.UTF16View.IndexDistance
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public typealias Indices = String.UTF16View.Indices
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public typealias SubSequence = String.UTF16View.Indices
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internal init(
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_elements: String.UTF16View,
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startIndex: Index,
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endIndex: Index
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) {
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self._elements = _elements
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self._startIndex = startIndex
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self._endIndex = endIndex
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}
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public var startIndex: Index {
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return _startIndex
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}
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public var endIndex: Index {
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return _endIndex
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}
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public var indices: Indices {
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return self
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}
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public subscript(i: Index) -> Index {
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// FIXME: swift-3-indexing-model: range check.
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return i
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}
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public subscript(bounds: Range<Index>) -> String.UTF16View.Indices {
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// FIXME: swift-3-indexing-model: range check.
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return String.UTF16View.Indices(
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_elements: _elements,
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startIndex: bounds.lowerBound,
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endIndex: bounds.upperBound)
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}
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public func index(after i: Index) -> Index {
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// FIXME: swift-3-indexing-model: range check.
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return _elements.index(after: i)
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}
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public func formIndex(after i: inout Index) {
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// FIXME: swift-3-indexing-model: range check.
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_elements.formIndex(after: &i)
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}
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public func index(before i: Index) -> Index {
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// FIXME: swift-3-indexing-model: range check.
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return _elements.index(before: i)
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}
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public func formIndex(before i: inout Index) {
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// FIXME: swift-3-indexing-model: range check.
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_elements.formIndex(before: &i)
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}
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public func index(_ i: Index, offsetBy n: IndexDistance) -> Index {
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// FIXME: swift-3-indexing-model: range check i?
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return _elements.index(i, offsetBy: n)
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}
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public func index(
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_ i: Index, offsetBy n: IndexDistance, limitedBy limit: Index
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) -> Index? {
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// FIXME: swift-3-indexing-model: range check i?
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return _elements.index(i, offsetBy: n, limitedBy: limit)
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}
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// TODO: swift-3-indexing-model - add docs
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public func distance(from start: Index, to end: Index) -> IndexDistance {
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// FIXME: swift-3-indexing-model: range check start and end?
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return _elements.distance(from: start, to: end)
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}
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}
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// backward compatibility for index interchange.
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extension String.UTF16View {
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@available(
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swift, obsoleted: 4.0,
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message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
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public func index(after i: Index?) -> Index {
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return index(after: i)
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}
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@available(
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swift, obsoleted: 4.0,
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message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
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public func index(
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_ i: Index?, offsetBy n: IndexDistance) -> Index {
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return index(i!, offsetBy: n)
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}
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@available(
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swift, obsoleted: 4.0,
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message: "Any String view index conversion can fail in Swift 4; please unwrap the optional indices")
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public func distance(from i: Index?, to j: Index?) -> IndexDistance {
|
||
return distance(from: i!, to: j!)
|
||
}
|
||
@available(
|
||
swift, obsoleted: 4.0,
|
||
message: "Any String view index conversion can fail in Swift 4; please unwrap the optional index")
|
||
public subscript(i: Index?) -> Unicode.UTF16.CodeUnit {
|
||
return self[i!]
|
||
}
|
||
}
|