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a51e32ad37
- Clarify StringProtocol conformance - Deprecate ExpressibleByStringInterpolation - String index conversions docs - Describe shared string indices
552 lines
19 KiB
Swift
552 lines
19 KiB
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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extension String {
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/// A view of a string's contents as a collection of Unicode scalar values.
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///
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/// You can access a string's view of Unicode scalar values by using its
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/// `unicodeScalars` property. Unicode scalar values are the 21-bit codes
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/// that are the basic unit of Unicode. Each scalar value is represented by
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/// a `Unicode.Scalar` instance and is equivalent to a UTF-32 code unit.
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///
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/// let flowers = "Flowers 💐"
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/// for v in flowers.unicodeScalars {
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/// print(v.value)
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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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/// // 128144
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///
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/// Some characters that are visible in a string are made up of more than one
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/// Unicode scalar value. In that case, a string's `unicodeScalars` view
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/// contains more elements than the string itself.
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///
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/// let flag = "🇵🇷"
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/// for c in flag {
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/// print(c)
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/// }
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/// // 🇵🇷
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///
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/// for v in flag.unicodeScalars {
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/// print(v.value)
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/// }
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/// // 127477
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/// // 127479
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///
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/// You can convert a `String.UnicodeScalarView` instance back into a string
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/// using the `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.unicodeScalars.index(where: { $0.value >= 128 }) {
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/// let asciiPrefix = String(favemoji.unicodeScalars[..<i])
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/// print(asciiPrefix)
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/// }
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/// // Prints "My favorite emoji is "
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public struct UnicodeScalarView :
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BidirectionalCollection,
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CustomStringConvertible,
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CustomDebugStringConvertible
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{
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internal init(_ _core: _StringCore, coreOffset: Int = 0) {
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self._core = _core
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self._coreOffset = coreOffset
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}
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internal struct _ScratchIterator : IteratorProtocol {
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var core: _StringCore
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var idx: Int
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@_versioned
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init(_ core: _StringCore, _ pos: Int) {
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self.idx = pos
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self.core = core
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}
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@inline(__always)
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mutating func next() -> UTF16.CodeUnit? {
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if idx == core.endIndex {
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return nil
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}
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defer { idx += 1 }
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return self.core[idx]
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}
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}
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public typealias Index = String.Index
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public typealias IndexDistance = Int
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/// Translates a `_core` index into a `UnicodeScalarIndex` using this view's
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/// `_coreOffset`.
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internal func _fromCoreIndex(_ i: Int) -> Index {
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return Index(encodedOffset: i + _coreOffset)
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}
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/// Translates a `UnicodeScalarIndex` into a `_core` index using this view's
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/// `_coreOffset`.
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internal func _toCoreIndex(_ i: Index) -> Int {
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return i.encodedOffset - _coreOffset
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}
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/// The position of the first Unicode scalar value if the string is
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/// nonempty.
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///
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/// If the string is empty, `startIndex` is equal to `endIndex`.
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public var startIndex: Index {
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return _fromCoreIndex(_core.startIndex)
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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 Unicode scalars view, `endIndex` is equal to `startIndex`.
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public var endIndex: Index {
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return _fromCoreIndex(_core.endIndex)
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}
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/// Returns the next consecutive location after `i`.
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///
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/// - Precondition: The next location exists.
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public func index(after i: Index) -> Index {
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let i = _toCoreIndex(i)
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var scratch = _ScratchIterator(_core, i)
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var decoder = UTF16()
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let (_, length) = decoder._decodeOne(&scratch)
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return _fromCoreIndex(i + length)
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}
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/// Returns the previous consecutive location before `i`.
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///
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/// - Precondition: The previous location exists.
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public func index(before i: Index) -> Index {
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var i = _toCoreIndex(i) - 1
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let codeUnit = _core[i]
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if _slowPath((codeUnit >> 10) == 0b1101_11) {
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if i != 0 && (_core[i - 1] >> 10) == 0b1101_10 {
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i -= 1
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}
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}
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return _fromCoreIndex(i)
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}
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/// Accesses the Unicode scalar value at the given position.
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///
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/// The following example searches a string's Unicode scalars view for a
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/// capital letter and then prints the character and Unicode scalar value
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/// at the found index:
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///
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/// let greeting = "Hello, friend!"
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/// if let i = greeting.unicodeScalars.index(where: { "A"..."Z" ~= $0 }) {
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/// print("First capital letter: \(greeting.unicodeScalars[i])")
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/// print("Unicode scalar value: \(greeting.unicodeScalars[i].value)")
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/// }
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/// // Prints "First capital letter: H"
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/// // Prints "Unicode scalar value: 72"
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///
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/// - Parameter position: A valid index of the character view. `position`
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/// must be less than the view's end index.
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public subscript(position: Index) -> Unicode.Scalar {
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var scratch = _ScratchIterator(_core, _toCoreIndex(position))
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var decoder = UTF16()
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switch decoder.decode(&scratch) {
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case .scalarValue(let us):
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return us
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case .emptyInput:
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_sanityCheckFailure("cannot subscript using an endIndex")
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case .error:
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return Unicode.Scalar(0xfffd)!
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}
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}
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/// An iterator over the Unicode scalars that make up a `UnicodeScalarView`
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/// collection.
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public struct Iterator : IteratorProtocol {
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init(_ _base: _StringCore) {
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self._iterator = _base.makeIterator()
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if _base.hasContiguousStorage {
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self._baseSet = true
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if _base.isASCII {
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self._ascii = true
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self._asciiBase = UnsafeBufferPointer(
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start: _base._baseAddress?.assumingMemoryBound(
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to: UTF8.CodeUnit.self),
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count: _base.count).makeIterator()
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} else {
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self._ascii = false
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self._base = UnsafeBufferPointer<UInt16>(
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start: _base._baseAddress?.assumingMemoryBound(
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to: UTF16.CodeUnit.self),
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count: _base.count).makeIterator()
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}
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} else {
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self._ascii = false
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self._baseSet = false
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}
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}
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/// Advances to the next element and returns it, or `nil` if no next
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/// element exists.
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///
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/// Once `nil` has been returned, all subsequent calls return `nil`.
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///
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/// - Precondition: `next()` has not been applied to a copy of `self`
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/// since the copy was made.
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public mutating func next() -> Unicode.Scalar? {
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var result: UnicodeDecodingResult
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if _baseSet {
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if _ascii {
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switch self._asciiBase.next() {
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case let x?:
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result = .scalarValue(Unicode.Scalar(x))
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case nil:
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result = .emptyInput
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}
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} else {
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result = _decoder.decode(&(self._base!))
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}
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} else {
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result = _decoder.decode(&(self._iterator))
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}
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switch result {
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case .scalarValue(let us):
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return us
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case .emptyInput:
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return nil
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case .error:
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return Unicode.Scalar(0xfffd)
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}
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}
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internal var _decoder: UTF16 = UTF16()
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internal let _baseSet: Bool
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internal let _ascii: Bool
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internal var _asciiBase: UnsafeBufferPointerIterator<UInt8>!
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internal var _base: UnsafeBufferPointerIterator<UInt16>!
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internal var _iterator: IndexingIterator<_StringCore>
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}
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/// Returns an iterator over the Unicode scalars that make up this view.
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///
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/// - Returns: An iterator over this collection's `Unicode.Scalar` elements.
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public func makeIterator() -> Iterator {
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return Iterator(_core)
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}
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public var description: String {
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return String(_core)
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}
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public var debugDescription: String {
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return "StringUnicodeScalarView(\(self.description.debugDescription))"
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}
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internal var _core: _StringCore
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/// The offset of this view's `_core` from an original core. This works
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/// around the fact that `_StringCore` is always zero-indexed.
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/// `_coreOffset` should be subtracted from `UnicodeScalarIndex.encodedOffset`
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/// before that value is used as a `_core` index.
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internal var _coreOffset: Int
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}
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/// Creates a string corresponding to the given collection of Unicode
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/// scalars.
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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 `unicodeScalars` view.
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///
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/// let picnicGuest = "Deserving porcupine"
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/// if let i = picnicGuest.unicodeScalars.index(of: " ") {
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/// let adjective = String(picnicGuest.unicodeScalars[..<i])
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/// print(adjective)
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/// }
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/// // Prints "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.unicodeScalars` view.
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///
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/// - Parameter unicodeScalars: A collection of Unicode scalar values.
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public init(_ unicodeScalars: UnicodeScalarView) {
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self.init(unicodeScalars._core)
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}
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/// The index type for a string's `unicodeScalars` view.
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public typealias UnicodeScalarIndex = UnicodeScalarView.Index
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}
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extension String.UnicodeScalarView : _SwiftStringView {
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var _persistentContent : String { return String(_core) }
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}
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extension String {
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/// The string's value represented as a collection of Unicode scalar values.
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public var unicodeScalars: UnicodeScalarView {
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get {
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return UnicodeScalarView(_core)
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}
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set {
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_core = newValue._core
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}
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}
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}
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extension String.UnicodeScalarView : RangeReplaceableCollection {
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/// Creates an empty view instance.
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public init() {
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self = String.UnicodeScalarView(_StringCore())
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}
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/// Reserves enough space in the view's underlying storage to store the
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/// specified number of ASCII characters.
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///
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/// Because a Unicode scalar value can require more than a single ASCII
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/// character's worth of storage, additional allocation may be necessary
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/// when adding to a Unicode scalar view after a call to
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/// `reserveCapacity(_:)`.
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///
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/// - Parameter n: The minimum number of ASCII character's worth of storage
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/// to allocate.
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///
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/// - Complexity: O(*n*), where *n* is the capacity being reserved.
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public mutating func reserveCapacity(_ n: Int) {
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_core.reserveCapacity(n)
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}
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/// Appends the given Unicode scalar to the view.
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///
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/// - Parameter c: The character to append to the string.
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public mutating func append(_ x: Unicode.Scalar) {
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_core.append(x)
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}
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/// Appends the Unicode scalar values in the given sequence to the view.
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///
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/// - Parameter newElements: A sequence of Unicode scalar values.
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///
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/// - Complexity: O(*n*), where *n* is the length of the resulting view.
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public mutating func append<S : Sequence>(contentsOf newElements: S)
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where S.Element == Unicode.Scalar {
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_core.append(contentsOf: newElements.lazy.flatMap { $0.utf16 })
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}
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/// Replaces the elements within the specified bounds with the given Unicode
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/// scalar values.
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///
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/// Calling this method invalidates any existing indices for use with this
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/// string.
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///
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/// - Parameters:
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/// - bounds: The range of elements to replace. The bounds of the range
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/// must be valid indices of the view.
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/// - newElements: The new Unicode scalar values to add to the string.
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///
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/// - Complexity: O(*m*), where *m* is the combined length of the view and
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/// `newElements`. If the call to `replaceSubrange(_:with:)` simply
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/// removes elements at the end of the string, the complexity is O(*n*),
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/// where *n* is equal to `bounds.count`.
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public mutating func replaceSubrange<C>(
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_ bounds: Range<Index>,
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with newElements: C
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) where C : Collection, C.Element == Unicode.Scalar {
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let rawSubRange: Range<Int> = _toCoreIndex(bounds.lowerBound) ..<
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_toCoreIndex(bounds.upperBound)
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let lazyUTF16 = newElements.lazy.flatMap { $0.utf16 }
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_core.replaceSubrange(rawSubRange, with: lazyUTF16)
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}
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}
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// Index conversions
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extension String.UnicodeScalarIndex {
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/// Creates an index in the given Unicode scalars view that corresponds
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/// exactly to the specified `UTF16View` position.
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///
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/// The following example finds the position of a space in a string's `utf16`
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/// view and then converts that position to an index in the string's
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/// `unicodeScalars` view:
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///
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/// let cafe = "Café 🍵"
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///
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/// let utf16Index = cafe.utf16.index(of: 32)!
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/// let scalarIndex = String.Index(utf16Index, within: cafe.unicodeScalars)!
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///
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/// print(String(cafe.unicodeScalars[..<scalarIndex]))
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/// // Prints "Café"
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///
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/// If the index passed as `sourcePosition` doesn't have an exact
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/// corresponding position in `unicodeScalars`, the result of the
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/// initializer is `nil`. For example, an attempt to convert the position of
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/// the trailing surrogate of a UTF-16 surrogate pair results in `nil`.
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///
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/// - Parameters:
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/// - sourcePosition: A position in the `utf16` view of a string. `utf16Index`
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/// must be an element of `String(unicodeScalars).utf16.indices`.
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/// - unicodeScalars: The `UnicodeScalarView` in which to find the new
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/// position.
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public init?(
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_ sourcePosition: String.UTF16Index,
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within unicodeScalars: String.UnicodeScalarView
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) {
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if !unicodeScalars._isOnUnicodeScalarBoundary(sourcePosition) { return nil }
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self = sourcePosition
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}
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/// Returns the position in the given string that corresponds exactly to this
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/// index.
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///
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/// This example first finds the position of a space (UTF-8 code point `32`)
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/// in a string's `utf8` view and then uses this method find the same position
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/// in the string.
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///
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/// let cafe = "Café 🍵"
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/// let i = cafe.unicodeScalars.index(of: "🍵")
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/// let j = i.samePosition(in: cafe)!
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/// print(cafe[j...])
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/// // Prints "🍵"
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///
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/// - Parameter characters: The string to use for the index conversion.
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/// This index must be a valid index of at least one view of `characters`.
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/// - Returns: The position in `characters` 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 `characters`, this method returns `nil`. For example,
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/// an attempt to convert the position of a UTF-8 continuation byte
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/// returns `nil`.
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public func samePosition(in characters: String) -> String.Index? {
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return String.Index(self, within: characters)
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}
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}
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extension String.UnicodeScalarView {
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internal func _isOnUnicodeScalarBoundary(_ i: Index) -> Bool {
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if _fastPath(_core.isASCII) { return true }
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if i == startIndex || i == endIndex {
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return true
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}
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if i._transcodedOffset != 0 { return false }
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let i2 = _toCoreIndex(i)
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if _fastPath(_core[i2] & 0xFC00 != 0xDC00) { return true }
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return _core[i2 &- 1] & 0xFC00 != 0xD800
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}
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// NOTE: Don't make this function inlineable. Grapheme cluster
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// segmentation uses a completely different algorithm in Unicode 9.0.
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internal func _isOnGraphemeClusterBoundary(_ i: Index) -> Bool {
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if i == startIndex || i == endIndex {
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return true
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}
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if !_isOnUnicodeScalarBoundary(i) { return false }
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let precedingScalar = self[index(before: i)]
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let graphemeClusterBreakProperty =
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_UnicodeGraphemeClusterBreakPropertyTrie()
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let segmenter = _UnicodeExtendedGraphemeClusterSegmenter()
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let gcb0 = graphemeClusterBreakProperty.getPropertyRawValue(
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precedingScalar.value)
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if segmenter.isBoundaryAfter(gcb0) {
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return true
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}
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let gcb1 = graphemeClusterBreakProperty.getPropertyRawValue(self[i].value)
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return segmenter.isBoundary(gcb0, gcb1)
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}
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}
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// Reflection
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extension String.UnicodeScalarView : CustomReflectable {
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/// Returns a mirror that reflects the Unicode scalars 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.UnicodeScalarView : 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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// backward compatibility for index interchange.
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extension String.UnicodeScalarView {
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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(_ 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 {
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return distance(from: i!, to: j!)
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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 subscript(i: Index?) -> Unicode.Scalar {
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return self[i!]
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}
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}
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//===--- Slicing Support --------------------------------------------------===//
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/// In Swift 3.2, in the absence of type context,
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///
|
|
/// someString.unicodeScalars[
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|
/// someString.unicodeScalars.startIndex
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|
/// ..< someString.unicodeScalars.endIndex]
|
|
///
|
|
/// was deduced to be of type `String.UnicodeScalarView`. Provide a
|
|
/// more-specific Swift-3-only `subscript` overload that continues to produce
|
|
/// `String.UnicodeScalarView`.
|
|
extension String.UnicodeScalarView {
|
|
public typealias SubSequence = Substring.UnicodeScalarView
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|
|
|
@available(swift, introduced: 4)
|
|
public subscript(r: Range<Index>) -> String.UnicodeScalarView.SubSequence {
|
|
return String.UnicodeScalarView.SubSequence(self, _bounds: r)
|
|
}
|
|
|
|
/// Accesses the Unicode scalar values in the given range.
|
|
///
|
|
/// The example below uses this subscript to access the scalar values up
|
|
/// to, but not including, the first comma (`","`) in the string.
|
|
///
|
|
/// let str = "All this happened, more or less."
|
|
/// let i = str.unicodeScalars.index(of: ",")!
|
|
/// let substring = str.unicodeScalars[str.unicodeScalars.startIndex ..< i]
|
|
/// print(String(substring))
|
|
/// // Prints "All this happened"
|
|
///
|
|
/// - Complexity: O(*n*) if the underlying string is bridged from
|
|
/// Objective-C, where *n* is the length of the string; otherwise, O(1).
|
|
@available(swift, obsoleted: 4)
|
|
public subscript(r: Range<Index>) -> String.UnicodeScalarView {
|
|
let rawSubRange = _toCoreIndex(r.lowerBound)..<_toCoreIndex(r.upperBound)
|
|
return String.UnicodeScalarView(
|
|
_core[rawSubRange], coreOffset: r.lowerBound.encodedOffset)
|
|
}
|
|
|
|
@available(swift, obsoleted: 4)
|
|
public subscript(bounds: ClosedRange<Index>) -> String.UnicodeScalarView {
|
|
return self[bounds.relative(to: self)]
|
|
}
|
|
}
|