stdlib/public/core/StringCharacterView.swift - third_party/swift - Git at Google

 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the Swift.org open source project
 //
 // Copyright (c) 2014 - 2018 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
 //
 //===----------------------------------------------------------------------===//

 // String is a bidirectional collection of `Character`s, aka graphemes
 extension String: BidirectionalCollection {
   /// A type that represents the number of steps between two `String.Index`
   /// values, where one value is reachable from the other.
   ///
   /// In Swift, *reachability* refers to the ability to produce one value from
   /// the other through zero or more applications of `index(after:)`.
   public typealias IndexDistance = Int

   public typealias SubSequence = Substring

   /// The position of the first character in a nonempty string.
   ///
   /// In an empty string, `startIndex` is equal to `endIndex`.
   @inlinable // FIXME(sil-serialize-all)
   public var startIndex: Index { return Index(encodedOffset: 0) }

   /// A string's "past the end" position---that is, the position one greater
   /// than the last valid subscript argument.
   ///
   /// In an empty string, `endIndex` is equal to `startIndex`.
   @inlinable // FIXME(sil-serialize-all)
   public var endIndex: Index { return Index(encodedOffset: _guts.count) }

   /// The number of characters in a string.
   public var count: Int {
     return distance(from: startIndex, to: 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`.
   public func index(after i: Index) -> Index {
     return _visitGuts(_guts, args: i,
       ascii: { ascii, i in ascii.characterIndex(after: i) },
       utf16: { utf16, i in utf16.characterIndex(after: i) },
       opaque: { opaque, i in opaque.characterIndex(after: i) })
   }

   /// 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`.
   public func index(before i: Index) -> Index {
     return _visitGuts(_guts, args: i,
       ascii: { ascii, i in ascii.characterIndex(before: i) },
       utf16: { utf16, i in utf16.characterIndex(before: i) },
       opaque: { opaque, i in opaque.characterIndex(before: i) })
   }

   /// 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`.
   /// - 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(*k*), where *k* is the absolute value of `distance`.
   public func index(_ i: Index, offsetBy distance: IndexDistance) -> Index {
     return _visitGuts(_guts, args: (i, distance),
       ascii: { ascii, args in let (i, n) = args
         return ascii.characterIndex(i, offsetBy: n) },
       utf16: { utf16, args in let (i, n) = args
         return utf16.characterIndex(i, offsetBy: n) },
       opaque: { opaque, args in let (i, n) = args
         return opaque.characterIndex(i, offsetBy: n) })
   }

   /// 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`.
   ///   - 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(*k*), where *k* is the absolute value of `distance`.
   public func index(
     _ i: Index, offsetBy distance: IndexDistance, limitedBy limit: Index
   ) -> Index? {
     return _visitGuts(_guts, args: (i, distance, limit),
       ascii: { ascii, args in let (i, n, limit) = args
         return ascii.characterIndex(i, offsetBy: n, limitedBy: limit) },
       utf16: { utf16, args in let (i, n, limit) = args
         return utf16.characterIndex(i, offsetBy: n, limitedBy: limit) },
       opaque: { opaque, args in let (i, n, limit) = args
         return opaque.characterIndex(i, offsetBy: n, limitedBy: limit) })
   }

   /// 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(*k*), where *k* is the resulting distance.
   public func distance(from start: Index, to end: Index) -> IndexDistance {
     return _visitGuts(_guts, args: (start, end),
       ascii: { ascii, args in let (start, end) = args
         return ascii.characterDistance(from: start, to: end) },
       utf16: { utf16, args in let (start, end) = args
         return utf16.characterDistance(from: start, to: end) },
       opaque: { opaque, args in let (start, end) = args
         return opaque.characterDistance(from: start, to: end) })
   }

   /// Accesses the character at the given position.
   ///
   /// You can use the same indices for subscripting a string and its substring.
   /// For example, this code finds the first letter after the first space:
   ///
   ///     let str = "Greetings, friend! How are you?"
   ///     let firstSpace = str.firstIndex(of: " ") ?? str.endIndex
   ///     let substr = str[firstSpace...]
   ///     if let nextCapital = substr.firstIndex(where: { $0 >= "A" && $0 <= "Z" }) {
   ///         print("Capital after a space: \(str[nextCapital])")
   ///     }
   ///     // Prints "Capital after a space: H"
   ///
   /// - Parameter i: A valid index of the string. `i` must be less than the
   ///   string's end index.
   public subscript(i: Index) -> Character {
     return _visitGuts(_guts, args: i,
       ascii: { ascii, i in return ascii.character(at: i) },
       utf16: { utf16, i in return utf16.character(at: i) },
       opaque: { opaque, i in return opaque.character(at: i) })
   }
 }
	//===----------------------------------------------------------------------===//
	//
	// This source file is part of the Swift.org open source project
	//
	// Copyright (c) 2014 - 2018 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
	//
	//===----------------------------------------------------------------------===//

	// String is a bidirectional collection of `Character`s, aka graphemes
	extension String: BidirectionalCollection {
	/// A type that represents the number of steps between two `String.Index`
	/// values, where one value is reachable from the other.
	///
	/// In Swift, reachability refers to the ability to produce one value from
	/// the other through zero or more applications of `index(after:)`.
	public typealias IndexDistance = Int

	public typealias SubSequence = Substring

	/// The position of the first character in a nonempty string.
	///
	/// In an empty string, `startIndex` is equal to `endIndex`.
	@inlinable // FIXME(sil-serialize-all)
	public var startIndex: Index { return Index(encodedOffset: 0) }

	/// A string's "past the end" position---that is, the position one greater
	/// than the last valid subscript argument.
	///
	/// In an empty string, `endIndex` is equal to `startIndex`.
	@inlinable // FIXME(sil-serialize-all)
	public var endIndex: Index { return Index(encodedOffset: _guts.count) }

	/// The number of characters in a string.
	public var count: Int {
	return distance(from: startIndex, to: 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`.
	public func index(after i: Index) -> Index {
	return _visitGuts(_guts, args: i,
	ascii: { ascii, i in ascii.characterIndex(after: i) },
	utf16: { utf16, i in utf16.characterIndex(after: i) },
	opaque: { opaque, i in opaque.characterIndex(after: i) })
	}

	/// 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`.
	public func index(before i: Index) -> Index {
	return _visitGuts(_guts, args: i,
	ascii: { ascii, i in ascii.characterIndex(before: i) },
	utf16: { utf16, i in utf16.characterIndex(before: i) },
	opaque: { opaque, i in opaque.characterIndex(before: i) })
	}

	/// 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`.
	/// - 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(k), where k is the absolute value of `distance`.
	public func index(_ i: Index, offsetBy distance: IndexDistance) -> Index {
	return _visitGuts(_guts, args: (i, distance),
	ascii: { ascii, args in let (i, n) = args
	return ascii.characterIndex(i, offsetBy: n) },
	utf16: { utf16, args in let (i, n) = args
	return utf16.characterIndex(i, offsetBy: n) },
	opaque: { opaque, args in let (i, n) = args
	return opaque.characterIndex(i, offsetBy: n) })
	}

	/// 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`.
	/// - 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(k), where k is the absolute value of `distance`.
	public func index(
	_ i: Index, offsetBy distance: IndexDistance, limitedBy limit: Index
	) -> Index? {
	return _visitGuts(_guts, args: (i, distance, limit),
	ascii: { ascii, args in let (i, n, limit) = args
	return ascii.characterIndex(i, offsetBy: n, limitedBy: limit) },
	utf16: { utf16, args in let (i, n, limit) = args
	return utf16.characterIndex(i, offsetBy: n, limitedBy: limit) },
	opaque: { opaque, args in let (i, n, limit) = args
	return opaque.characterIndex(i, offsetBy: n, limitedBy: limit) })
	}

	/// 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(k), where k is the resulting distance.
	public func distance(from start: Index, to end: Index) -> IndexDistance {
	return _visitGuts(_guts, args: (start, end),
	ascii: { ascii, args in let (start, end) = args
	return ascii.characterDistance(from: start, to: end) },
	utf16: { utf16, args in let (start, end) = args
	return utf16.characterDistance(from: start, to: end) },
	opaque: { opaque, args in let (start, end) = args
	return opaque.characterDistance(from: start, to: end) })
	}

	/// Accesses the character at the given position.
	///
	/// You can use the same indices for subscripting a string and its substring.
	/// For example, this code finds the first letter after the first space:
	///
	/// let str = "Greetings, friend! How are you?"
	/// let firstSpace = str.firstIndex(of: " ") ?? str.endIndex
	/// let substr = str[firstSpace...]
	/// if let nextCapital = substr.firstIndex(where: { $0 >= "A" && $0 <= "Z" }) {
	/// print("Capital after a space: \(str[nextCapital])")
	/// }
	/// // Prints "Capital after a space: H"
	///
	/// - Parameter i: A valid index of the string. `i` must be less than the
	/// string's end index.
	public subscript(i: Index) -> Character {
	return _visitGuts(_guts, args: i,
	ascii: { ascii, i in return ascii.character(at: i) },
	utf16: { utf16, i in return utf16.character(at: i) },
	opaque: { opaque, i in return opaque.character(at: i) })
	}
	}