| //===----------------------------------------------------------------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| |
| /// A type that iterates over a collection using its indices. |
| /// |
| /// The `IndexingIterator` type is the default iterator for any collection that |
| /// doesn't declare its own. It acts as an iterator by using a collection's |
| /// indices to step over each value in the collection. Most collections in the |
| /// standard library use `IndexingIterator` as their iterator. |
| /// |
| /// By default, any custom collection type you create will inherit a |
| /// `makeIterator()` method that returns an `IndexingIterator` instance, |
| /// making it unnecessary to declare your own. When creating a custom |
| /// collection type, add the minimal requirements of the `Collection` |
| /// protocol: starting and ending indices and a subscript for accessing |
| /// elements. With those elements defined, the inherited `makeIterator()` |
| /// method satisfies the requirements of the `Sequence` protocol. |
| /// |
| /// Here's an example of a type that declares the minimal requirements for a |
| /// collection. The `CollectionOfTwo` structure is a fixed-size collection |
| /// that always holds two elements of a specific type. |
| /// |
| /// struct CollectionOfTwo<Element>: Collection { |
| /// let elements: (Element, Element) |
| /// |
| /// init(_ first: Element, _ second: Element) { |
| /// self.elements = (first, second) |
| /// } |
| /// |
| /// var startIndex: Int { return 0 } |
| /// var endIndex: Int { return 2 } |
| /// |
| /// subscript(index: Int) -> Element { |
| /// switch index { |
| /// case 0: return elements.0 |
| /// case 1: return elements.1 |
| /// default: fatalError("Index out of bounds.") |
| /// } |
| /// } |
| /// |
| /// func index(after i: Int) -> Int { |
| /// precondition(i < endIndex, "Can't advance beyond endIndex") |
| /// return i + 1 |
| /// } |
| /// } |
| /// |
| /// Because `CollectionOfTwo` doesn't define its own `makeIterator()` |
| /// method or `Iterator` associated type, it uses the default iterator type, |
| /// `IndexingIterator`. This example shows how a `CollectionOfTwo` instance |
| /// can be created holding the values of a point, and then iterated over |
| /// using a `for`-`in` loop. |
| /// |
| /// let point = CollectionOfTwo(15.0, 20.0) |
| /// for element in point { |
| /// print(element) |
| /// } |
| /// // Prints "15.0" |
| /// // Prints "20.0" |
| @_fixed_layout |
| public struct IndexingIterator<Elements : Collection> { |
| @usableFromInline |
| internal let _elements: Elements |
| @usableFromInline |
| internal var _position: Elements.Index |
| |
| @inlinable |
| @inline(__always) |
| /// Creates an iterator over the given collection. |
| public /// @testable |
| init(_elements: Elements) { |
| self._elements = _elements |
| self._position = _elements.startIndex |
| } |
| |
| @inlinable |
| @inline(__always) |
| /// Creates an iterator over the given collection. |
| public /// @testable |
| init(_elements: Elements, _position: Elements.Index) { |
| self._elements = _elements |
| self._position = _position |
| } |
| } |
| |
| extension IndexingIterator: IteratorProtocol, Sequence { |
| public typealias Element = Elements.Element |
| public typealias Iterator = IndexingIterator<Elements> |
| public typealias SubSequence = AnySequence<Element> |
| |
| /// Advances to the next element and returns it, or `nil` if no next element |
| /// exists. |
| /// |
| /// Repeatedly calling this method returns all the elements of the underlying |
| /// sequence in order. As soon as the sequence has run out of elements, all |
| /// subsequent calls return `nil`. |
| /// |
| /// This example shows how an iterator can be used explicitly to emulate a |
| /// `for`-`in` loop. First, retrieve a sequence's iterator, and then call |
| /// the iterator's `next()` method until it returns `nil`. |
| /// |
| /// let numbers = [2, 3, 5, 7] |
| /// var numbersIterator = numbers.makeIterator() |
| /// |
| /// while let num = numbersIterator.next() { |
| /// print(num) |
| /// } |
| /// // Prints "2" |
| /// // Prints "3" |
| /// // Prints "5" |
| /// // Prints "7" |
| /// |
| /// - Returns: The next element in the underlying sequence if a next element |
| /// exists; otherwise, `nil`. |
| @inlinable |
| @inline(__always) |
| public mutating func next() -> Elements.Element? { |
| if _position == _elements.endIndex { return nil } |
| let element = _elements[_position] |
| _elements.formIndex(after: &_position) |
| return element |
| } |
| } |
| |
| /// A sequence whose elements can be traversed multiple times, |
| /// nondestructively, and accessed by an indexed subscript. |
| /// |
| /// Collections are used extensively throughout the standard library. When you |
| /// use arrays, dictionaries, and other collections, you benefit from the |
| /// operations that the `Collection` protocol declares and implements. In |
| /// addition to the operations that collections inherit from the `Sequence` |
| /// protocol, you gain access to methods that depend on accessing an element |
| /// at a specific position in a collection. |
| /// |
| /// For example, if you want to print only the first word in a string, you can |
| /// search for the index of the first space, and then create a substring up to |
| /// that position. |
| /// |
| /// let text = "Buffalo buffalo buffalo buffalo." |
| /// if let firstSpace = text.firstIndex(of: " ") { |
| /// print(text[..<firstSpace]) |
| /// } |
| /// // Prints "Buffalo" |
| /// |
| /// The `firstSpace` constant is an index into the `text` string---the position |
| /// of the first space in the string. You can store indices in variables, and |
| /// pass them to collection algorithms or use them later to access the |
| /// corresponding element. In the example above, `firstSpace` is used to |
| /// extract the prefix that contains elements up to that index. |
| /// |
| /// Accessing Individual Elements |
| /// ============================= |
| /// |
| /// You can access an element of a collection through its subscript by using |
| /// any valid index except the collection's `endIndex` property. This property |
| /// is a "past the end" index that does not correspond with any element of the |
| /// collection. |
| /// |
| /// Here's an example of accessing the first character in a string through its |
| /// subscript: |
| /// |
| /// let firstChar = text[text.startIndex] |
| /// print(firstChar) |
| /// // Prints "B" |
| /// |
| /// The `Collection` protocol declares and provides default implementations for |
| /// many operations that depend on elements being accessible by their |
| /// subscript. For example, you can also access the first character of `text` |
| /// using the `first` property, which has the value of the first element of |
| /// the collection, or `nil` if the collection is empty. |
| /// |
| /// print(text.first) |
| /// // Prints "Optional("B")" |
| /// |
| /// You can pass only valid indices to collection operations. You can find a |
| /// complete set of a collection's valid indices by starting with the |
| /// collection's `startIndex` property and finding every successor up to, and |
| /// including, the `endIndex` property. All other values of the `Index` type, |
| /// such as the `startIndex` property of a different collection, are invalid |
| /// indices for this collection. |
| /// |
| /// Saved indices may become invalid as a result of mutating operations. For |
| /// more information about index invalidation in mutable collections, see the |
| /// reference for the `MutableCollection` and `RangeReplaceableCollection` |
| /// protocols, as well as for the specific type you're using. |
| /// |
| /// Accessing Slices of a Collection |
| /// ================================ |
| /// |
| /// You can access a slice of a collection through its ranged subscript or by |
| /// calling methods like `prefix(while:)` or `suffix(_:)`. A slice of a |
| /// collection can contain zero or more of the original collection's elements |
| /// and shares the original collection's semantics. |
| /// |
| /// The following example creates a `firstWord` constant by using the |
| /// `prefix(while:)` method to get a slice of the `text` string. |
| /// |
| /// let firstWord = text.prefix(while: { $0 != " " }) |
| /// print(firstWord) |
| /// // Prints "Buffalo" |
| /// |
| /// You can retrieve the same slice using the string's ranged subscript, which |
| /// takes a range expression. |
| /// |
| /// if let firstSpace = text.firstIndex(of: " ") { |
| /// print(text[..<firstSpace] |
| /// // Prints "Buffalo" |
| /// } |
| /// |
| /// The retrieved slice of `text` is equivalent in each of these cases. |
| /// |
| /// Slices Share Indices |
| /// -------------------- |
| /// |
| /// A collection and its slices share the same indices. An element of a |
| /// collection is located under the same index in a slice as in the base |
| /// collection, as long as neither the collection nor the slice has been |
| /// mutated since the slice was created. |
| /// |
| /// For example, suppose you have an array holding the number of absences from |
| /// each class during a session. |
| /// |
| /// var absences = [0, 2, 0, 4, 0, 3, 1, 0] |
| /// |
| /// You're tasked with finding the day with the most absences in the second |
| /// half of the session. To find the index of the day in question, follow |
| /// these steps: |
| /// |
| /// 1) Create a slice of the `absences` array that holds the second half of the |
| /// days. |
| /// 2) Use the `max(by:)` method to determine the index of the day with the |
| /// most absences. |
| /// 3) Print the result using the index found in step 2 on the original |
| /// `absences` array. |
| /// |
| /// Here's an implementation of those steps: |
| /// |
| /// let secondHalf = absences.suffix(absences.count / 2) |
| /// if let i = secondHalf.indices.max(by: { secondHalf[$0] < secondHalf[$1] }) { |
| /// print("Highest second-half absences: \(absences[i])") |
| /// } |
| /// // Prints "Highest second-half absences: 3" |
| /// |
| /// Slices Inherit Collection Semantics |
| /// ----------------------------------- |
| /// |
| /// A slice inherits the value or reference semantics of its base collection. |
| /// That is, when working with a slice of a mutable collection that has value |
| /// semantics, such as an array, mutating the original collection triggers a |
| /// copy of that collection and does not affect the contents of the slice. |
| /// |
| /// For example, if you update the last element of the `absences` array from |
| /// `0` to `2`, the `secondHalf` slice is unchanged. |
| /// |
| /// absences[7] = 2 |
| /// print(absences) |
| /// // Prints "[0, 2, 0, 4, 0, 3, 1, 2]" |
| /// print(secondHalf) |
| /// // Prints "[0, 3, 1, 0]" |
| /// |
| /// Traversing a Collection |
| /// ======================= |
| /// |
| /// Although a sequence can be consumed as it is traversed, a collection is |
| /// guaranteed to be *multipass*: Any element can be repeatedly accessed by |
| /// saving its index. Moreover, a collection's indices form a finite range of |
| /// the positions of the collection's elements. The fact that all collections |
| /// are finite guarantees the safety of many sequence operations, such as |
| /// using the `contains(_:)` method to test whether a collection includes an |
| /// element. |
| /// |
| /// Iterating over the elements of a collection by their positions yields the |
| /// same elements in the same order as iterating over that collection using |
| /// its iterator. This example demonstrates that the `characters` view of a |
| /// string returns the same characters in the same order whether the view's |
| /// indices or the view itself is being iterated. |
| /// |
| /// let word = "Swift" |
| /// for character in word { |
| /// print(character) |
| /// } |
| /// // Prints "S" |
| /// // Prints "w" |
| /// // Prints "i" |
| /// // Prints "f" |
| /// // Prints "t" |
| /// |
| /// for i in word.indices { |
| /// print(word[i]) |
| /// } |
| /// // Prints "S" |
| /// // Prints "w" |
| /// // Prints "i" |
| /// // Prints "f" |
| /// // Prints "t" |
| /// |
| /// Conforming to the Collection Protocol |
| /// ===================================== |
| /// |
| /// If you create a custom sequence that can provide repeated access to its |
| /// elements, make sure that its type conforms to the `Collection` protocol in |
| /// order to give a more useful and more efficient interface for sequence and |
| /// collection operations. To add `Collection` conformance to your type, you |
| /// must declare at least the following requirements: |
| /// |
| /// - The `startIndex` and `endIndex` properties |
| /// - A subscript that provides at least read-only access to your type's |
| /// elements |
| /// - The `index(after:)` method for advancing an index into your collection |
| /// |
| /// Expected Performance |
| /// ==================== |
| /// |
| /// Types that conform to `Collection` are expected to provide the `startIndex` |
| /// and `endIndex` properties and subscript access to elements as O(1) |
| /// operations. Types that are not able to guarantee this performance must |
| /// document the departure, because many collection operations depend on O(1) |
| /// subscripting performance for their own performance guarantees. |
| /// |
| /// The performance of some collection operations depends on the type of index |
| /// that the collection provides. For example, a random-access collection, |
| /// which can measure the distance between two indices in O(1) time, can |
| /// calculate its `count` property in O(1) time. Conversely, because a forward |
| /// or bidirectional collection must traverse the entire collection to count |
| /// the number of contained elements, accessing its `count` property is an |
| /// O(*n*) operation. |
| public protocol Collection: Sequence { |
| // FIXME: ideally this would be in MigrationSupport.swift, but it needs |
| // to be on the protocol instead of as an extension |
| @available(*, deprecated/*, obsoleted: 5.0*/, message: "all index distances are now of type Int") |
| typealias IndexDistance = Int |
| |
| // FIXME: Associated type inference requires this. |
| override associatedtype Element |
| |
| /// A type that represents a position in the collection. |
| /// |
| /// Valid indices consist of the position of every element and a |
| /// "past the end" position that's not valid for use as a subscript |
| /// argument. |
| associatedtype Index : Comparable |
| |
| /// The position of the first element in a nonempty collection. |
| /// |
| /// If the collection is empty, `startIndex` is equal to `endIndex`. |
| var startIndex: Index { get } |
| |
| /// The collection's "past the end" position---that is, the position one |
| /// greater than the last valid subscript argument. |
| /// |
| /// When you need a range that includes the last element of a collection, use |
| /// the half-open range operator (`..<`) with `endIndex`. The `..<` operator |
| /// creates a range that doesn't include the upper bound, so it's always |
| /// safe to use with `endIndex`. For example: |
| /// |
| /// let numbers = [10, 20, 30, 40, 50] |
| /// if let index = numbers.firstIndex(of: 30) { |
| /// print(numbers[index ..< numbers.endIndex]) |
| /// } |
| /// // Prints "[30, 40, 50]" |
| /// |
| /// If the collection is empty, `endIndex` is equal to `startIndex`. |
| var endIndex: Index { get } |
| |
| /// A type that provides the collection's iteration interface and |
| /// encapsulates its iteration state. |
| /// |
| /// By default, a collection conforms to the `Sequence` protocol by |
| /// supplying `IndexingIterator` as its associated `Iterator` |
| /// type. |
| associatedtype Iterator = IndexingIterator<Self> |
| |
| // FIXME: Only needed for associated type inference. Otherwise, |
| // we get an `IndexingIterator` rather than properly deducing the |
| // Iterator type from makeIterator(). <rdar://problem/21539115> |
| /// Returns an iterator over the elements of the collection. |
| override func makeIterator() -> Iterator |
| |
| /// A sequence that represents a contiguous subrange of the collection's |
| /// elements. |
| /// |
| /// This associated type appears as a requirement in the `Sequence` |
| /// protocol, but it is restated here with stricter constraints. In a |
| /// collection, the subsequence should also conform to `Collection`. |
| associatedtype SubSequence: Collection = Slice<Self> |
| where SubSequence.Index == Index, |
| Element == SubSequence.Element, |
| SubSequence.SubSequence == SubSequence |
| |
| /// Accesses the element at the specified position. |
| /// |
| /// The following example accesses an element of an array through its |
| /// subscript to print its value: |
| /// |
| /// var streets = ["Adams", "Bryant", "Channing", "Douglas", "Evarts"] |
| /// print(streets[1]) |
| /// // Prints "Bryant" |
| /// |
| /// You can subscript a collection with any valid index other than the |
| /// collection's end index. The end index refers to the position one past |
| /// the last element of a collection, so it doesn't correspond with an |
| /// element. |
| /// |
| /// - Parameter position: The position of the element to access. `position` |
| /// must be a valid index of the collection that is not equal to the |
| /// `endIndex` property. |
| /// |
| /// - Complexity: O(1) |
| @_borrowed |
| subscript(position: Index) -> Element { get } |
| |
| /// Accesses a contiguous subrange of the collection's elements. |
| /// |
| /// For example, using a `PartialRangeFrom` range expression with an array |
| /// accesses the subrange from the start of the range expression until the |
| /// end of the array. |
| /// |
| /// let streets = ["Adams", "Bryant", "Channing", "Douglas", "Evarts"] |
| /// let streetsSlice = streets[2..<5] |
| /// print(streetsSlice) |
| /// // ["Channing", "Douglas", "Evarts"] |
| /// |
| /// The accessed slice uses the same indices for the same elements as the |
| /// original collection. This example searches `streetsSlice` for one of the |
| /// strings in the slice, and then uses that index in the original array. |
| /// |
| /// let index = streetsSlice.firstIndex(of: "Evarts")! // 4 |
| /// print(streets[index]) |
| /// // "Evarts" |
| /// |
| /// Always use the slice's `startIndex` property instead of assuming that its |
| /// indices start at a particular value. Attempting to access an element by |
| /// using an index outside the bounds of the slice may result in a runtime |
| /// error, even if that index is valid for the original collection. |
| /// |
| /// print(streetsSlice.startIndex) |
| /// // 2 |
| /// print(streetsSlice[2]) |
| /// // "Channing" |
| /// |
| /// print(streetsSlice[0]) |
| /// // error: Index out of bounds |
| /// |
| /// - Parameter bounds: A range of the collection's indices. The bounds of |
| /// the range must be valid indices of the collection. |
| /// |
| /// - Complexity: O(1) |
| subscript(bounds: Range<Index>) -> SubSequence { get } |
| |
| /// A type that represents the indices that are valid for subscripting the |
| /// collection, in ascending order. |
| associatedtype Indices : Collection = DefaultIndices<Self> |
| where Indices.Element == Index, |
| Indices.Index == Index, |
| Indices.SubSequence == Indices |
| |
| /// The indices that are valid for subscripting the collection, in ascending |
| /// order. |
| /// |
| /// A collection's `indices` property can hold a strong reference to the |
| /// collection itself, causing the collection to be nonuniquely referenced. |
| /// If you mutate the collection while iterating over its indices, a strong |
| /// reference can result in an unexpected copy of the collection. To avoid |
| /// the unexpected copy, use the `index(after:)` method starting with |
| /// `startIndex` to produce indices instead. |
| /// |
| /// var c = MyFancyCollection([10, 20, 30, 40, 50]) |
| /// var i = c.startIndex |
| /// while i != c.endIndex { |
| /// c[i] /= 5 |
| /// i = c.index(after: i) |
| /// } |
| /// // c == MyFancyCollection([2, 4, 6, 8, 10]) |
| var indices: Indices { get } |
| |
| /// A Boolean value indicating whether the collection is empty. |
| /// |
| /// When you need to check whether your collection is empty, use the |
| /// `isEmpty` property instead of checking that the `count` property is |
| /// equal to zero. For collections that don't conform to |
| /// `RandomAccessCollection`, accessing the `count` property iterates |
| /// through the elements of the collection. |
| /// |
| /// let horseName = "Silver" |
| /// if horseName.isEmpty { |
| /// print("I've been through the desert on a horse with no name.") |
| /// } else { |
| /// print("Hi ho, \(horseName)!") |
| /// } |
| /// // Prints "Hi ho, Silver!" |
| /// |
| /// - Complexity: O(1) |
| var isEmpty: Bool { get } |
| |
| /// The number of elements in the collection. |
| /// |
| /// To check whether a collection is empty, use its `isEmpty` property |
| /// instead of comparing `count` to zero. Unless the collection guarantees |
| /// random-access performance, calculating `count` can be an O(*n*) |
| /// operation. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length |
| /// of the collection. |
| var count: Int { get } |
| |
| // The following requirements enable dispatching for firstIndex(of:) and |
| // lastIndex(of:) when the element type is Equatable. |
| |
| /// Returns `Optional(Optional(index))` if an element was found |
| /// or `Optional(nil)` if an element was determined to be missing; |
| /// otherwise, `nil`. |
| /// |
| /// - Complexity: O(*n*), where *n* is the length of the collection. |
| func _customIndexOfEquatableElement(_ element: Element) -> Index?? |
| |
| /// Customization point for `Collection.lastIndex(of:)`. |
| /// |
| /// Define this method if the collection can find an element in less than |
| /// O(*n*) by exploiting collection-specific knowledge. |
| /// |
| /// - Returns: `nil` if a linear search should be attempted instead, |
| /// `Optional(nil)` if the element was not found, or |
| /// `Optional(Optional(index))` if an element was found. |
| /// |
| /// - Complexity: Hopefully less than O(`count`). |
| func _customLastIndexOfEquatableElement(_ element: Element) -> Index?? |
| |
| /// Returns an index that is the specified distance from the given index. |
| /// |
| /// The following example obtains an index advanced four positions from a |
| /// string's starting index and then prints the character at that position. |
| /// |
| /// let s = "Swift" |
| /// let i = s.index(s.startIndex, offsetBy: 4) |
| /// print(s[i]) |
| /// // Prints "t" |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// - Returns: An index offset by `distance` from the index `i`. If |
| /// `distance` is positive, this is the same value as the result of |
| /// `distance` calls to `index(after:)`. If `distance` is negative, this |
| /// is the same value as the result of `abs(distance)` calls to |
| /// `index(before:)`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| func index(_ i: Index, offsetBy distance: Int) -> Index |
| |
| /// Returns an index that is the specified distance from the given index, |
| /// unless that distance is beyond a given limiting index. |
| /// |
| /// The following example obtains an index advanced four positions from a |
| /// string's starting index and then prints the character at that position. |
| /// The operation doesn't require going beyond the limiting `s.endIndex` |
| /// value, so it succeeds. |
| /// |
| /// let s = "Swift" |
| /// if let i = s.index(s.startIndex, offsetBy: 4, limitedBy: s.endIndex) { |
| /// print(s[i]) |
| /// } |
| /// // Prints "t" |
| /// |
| /// The next example attempts to retrieve an index six positions from |
| /// `s.startIndex` but fails, because that distance is beyond the index |
| /// passed as `limit`. |
| /// |
| /// let j = s.index(s.startIndex, offsetBy: 6, limitedBy: s.endIndex) |
| /// print(j) |
| /// // Prints "nil" |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection, unless the index passed as `limit` prevents offsetting |
| /// beyond those bounds. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// - limit: A valid index of the collection to use as a limit. If |
| /// `distance > 0`, a limit that is less than `i` has no effect. |
| /// Likewise, if `distance < 0`, a limit that is greater than `i` has no |
| /// effect. |
| /// - Returns: An index offset by `distance` from the index `i`, unless that |
| /// index would be beyond `limit` in the direction of movement. In that |
| /// case, the method returns `nil`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| func index( |
| _ i: Index, offsetBy distance: Int, limitedBy limit: Index |
| ) -> Index? |
| |
| /// Returns the distance between two indices. |
| /// |
| /// Unless the collection conforms to the `BidirectionalCollection` protocol, |
| /// `start` must be less than or equal to `end`. |
| /// |
| /// - Parameters: |
| /// - start: A valid index of the collection. |
| /// - end: Another valid index of the collection. If `end` is equal to |
| /// `start`, the result is zero. |
| /// - Returns: The distance between `start` and `end`. The result can be |
| /// negative only if the collection conforms to the |
| /// `BidirectionalCollection` protocol. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the |
| /// resulting distance. |
| func distance(from start: Index, to end: Index) -> Int |
| |
| /// Performs a range check in O(1), or a no-op when a range check is not |
| /// implementable in O(1). |
| /// |
| /// The range check, if performed, is equivalent to: |
| /// |
| /// precondition(bounds.contains(index)) |
| /// |
| /// Use this function to perform a cheap range check for QoI purposes when |
| /// memory safety is not a concern. Do not rely on this range check for |
| /// memory safety. |
| /// |
| /// The default implementation for forward and bidirectional indices is a |
| /// no-op. The default implementation for random access indices performs a |
| /// range check. |
| /// |
| /// - Complexity: O(1). |
| func _failEarlyRangeCheck(_ index: Index, bounds: Range<Index>) |
| |
| func _failEarlyRangeCheck(_ index: Index, bounds: ClosedRange<Index>) |
| |
| /// Performs a range check in O(1), or a no-op when a range check is not |
| /// implementable in O(1). |
| /// |
| /// The range check, if performed, is equivalent to: |
| /// |
| /// precondition( |
| /// bounds.contains(range.lowerBound) || |
| /// range.lowerBound == bounds.upperBound) |
| /// precondition( |
| /// bounds.contains(range.upperBound) || |
| /// range.upperBound == bounds.upperBound) |
| /// |
| /// Use this function to perform a cheap range check for QoI purposes when |
| /// memory safety is not a concern. Do not rely on this range check for |
| /// memory safety. |
| /// |
| /// The default implementation for forward and bidirectional indices is a |
| /// no-op. The default implementation for random access indices performs a |
| /// range check. |
| /// |
| /// - Complexity: O(1). |
| func _failEarlyRangeCheck(_ range: Range<Index>, bounds: Range<Index>) |
| |
| /// Returns the position immediately after the given index. |
| /// |
| /// The successor of an index must be well defined. For an index `i` into a |
| /// collection `c`, calling `c.index(after: i)` returns the same index every |
| /// time. |
| /// |
| /// - Parameter i: A valid index of the collection. `i` must be less than |
| /// `endIndex`. |
| /// - Returns: The index value immediately after `i`. |
| func index(after i: Index) -> Index |
| |
| /// Replaces the given index with its successor. |
| /// |
| /// - Parameter i: A valid index of the collection. `i` must be less than |
| /// `endIndex`. |
| func formIndex(after i: inout Index) |
| } |
| |
| /// Default implementation for forward collections. |
| extension Collection { |
| /// Replaces the given index with its successor. |
| /// |
| /// - Parameter i: A valid index of the collection. `i` must be less than |
| /// `endIndex`. |
| @inlinable // protocol-only |
| @inline(__always) |
| public func formIndex(after i: inout Index) { |
| i = index(after: i) |
| } |
| |
| @inlinable |
| public func _failEarlyRangeCheck(_ index: Index, bounds: Range<Index>) { |
| // FIXME: swift-3-indexing-model: tests. |
| _precondition( |
| bounds.lowerBound <= index, |
| "Out of bounds: index < startIndex") |
| _precondition( |
| index < bounds.upperBound, |
| "Out of bounds: index >= endIndex") |
| } |
| |
| @inlinable |
| public func _failEarlyRangeCheck(_ index: Index, bounds: ClosedRange<Index>) { |
| // FIXME: swift-3-indexing-model: tests. |
| _precondition( |
| bounds.lowerBound <= index, |
| "Out of bounds: index < startIndex") |
| _precondition( |
| index <= bounds.upperBound, |
| "Out of bounds: index > endIndex") |
| } |
| |
| @inlinable |
| public func _failEarlyRangeCheck(_ range: Range<Index>, bounds: Range<Index>) { |
| // FIXME: swift-3-indexing-model: tests. |
| _precondition( |
| bounds.lowerBound <= range.lowerBound, |
| "Out of bounds: range begins before startIndex") |
| _precondition( |
| range.lowerBound <= bounds.upperBound, |
| "Out of bounds: range ends after endIndex") |
| _precondition( |
| bounds.lowerBound <= range.upperBound, |
| "Out of bounds: range ends before bounds.lowerBound") |
| _precondition( |
| range.upperBound <= bounds.upperBound, |
| "Out of bounds: range begins after bounds.upperBound") |
| } |
| |
| /// Returns an index that is the specified distance from the given index. |
| /// |
| /// The following example obtains an index advanced four positions from a |
| /// string's starting index and then prints the character at that position. |
| /// |
| /// let s = "Swift" |
| /// let i = s.index(s.startIndex, offsetBy: 4) |
| /// print(s[i]) |
| /// // Prints "t" |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// - Returns: An index offset by `distance` from the index `i`. If |
| /// `distance` is positive, this is the same value as the result of |
| /// `distance` calls to `index(after:)`. If `distance` is negative, this |
| /// is the same value as the result of `abs(distance)` calls to |
| /// `index(before:)`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| @inlinable |
| public func index(_ i: Index, offsetBy distance: Int) -> Index { |
| return self._advanceForward(i, by: distance) |
| } |
| |
| /// Returns an index that is the specified distance from the given index, |
| /// unless that distance is beyond a given limiting index. |
| /// |
| /// The following example obtains an index advanced four positions from a |
| /// string's starting index and then prints the character at that position. |
| /// The operation doesn't require going beyond the limiting `s.endIndex` |
| /// value, so it succeeds. |
| /// |
| /// let s = "Swift" |
| /// if let i = s.index(s.startIndex, offsetBy: 4, limitedBy: s.endIndex) { |
| /// print(s[i]) |
| /// } |
| /// // Prints "t" |
| /// |
| /// The next example attempts to retrieve an index six positions from |
| /// `s.startIndex` but fails, because that distance is beyond the index |
| /// passed as `limit`. |
| /// |
| /// let j = s.index(s.startIndex, offsetBy: 6, limitedBy: s.endIndex) |
| /// print(j) |
| /// // Prints "nil" |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection, unless the index passed as `limit` prevents offsetting |
| /// beyond those bounds. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// - limit: A valid index of the collection to use as a limit. If |
| /// `distance > 0`, a limit that is less than `i` has no effect. |
| /// Likewise, if `distance < 0`, a limit that is greater than `i` has no |
| /// effect. |
| /// - Returns: An index offset by `distance` from the index `i`, unless that |
| /// index would be beyond `limit` in the direction of movement. In that |
| /// case, the method returns `nil`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| @inlinable |
| public func index( |
| _ i: Index, offsetBy distance: Int, limitedBy limit: Index |
| ) -> Index? { |
| return self._advanceForward(i, by: distance, limitedBy: limit) |
| } |
| |
| /// Offsets the given index by the specified distance. |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| @inlinable |
| public func formIndex(_ i: inout Index, offsetBy distance: Int) { |
| i = index(i, offsetBy: distance) |
| } |
| |
| /// Offsets the given index by the specified distance, or so that it equals |
| /// the given limiting index. |
| /// |
| /// The value passed as `distance` must not offset `i` beyond the bounds of |
| /// the collection, unless the index passed as `limit` prevents offsetting |
| /// beyond those bounds. |
| /// |
| /// - Parameters: |
| /// - i: A valid index of the collection. |
| /// - distance: The distance to offset `i`. `distance` must not be negative |
| /// unless the collection conforms to the `BidirectionalCollection` |
| /// protocol. |
| /// - limit: A valid index of the collection to use as a limit. If |
| /// `distance > 0`, a limit that is less than `i` has no effect. |
| /// Likewise, if `distance < 0`, a limit that is greater than `i` has no |
| /// effect. |
| /// - Returns: `true` if `i` has been offset by exactly `distance` steps |
| /// without going beyond `limit`; otherwise, `false`. When the return |
| /// value is `false`, the value of `i` is equal to `limit`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the absolute |
| /// value of `distance`. |
| @inlinable |
| public func formIndex( |
| _ i: inout Index, offsetBy distance: Int, limitedBy limit: Index |
| ) -> Bool { |
| if let advancedIndex = index(i, offsetBy: distance, limitedBy: limit) { |
| i = advancedIndex |
| return true |
| } |
| i = limit |
| return false |
| } |
| |
| /// Returns the distance between two indices. |
| /// |
| /// Unless the collection conforms to the `BidirectionalCollection` protocol, |
| /// `start` must be less than or equal to `end`. |
| /// |
| /// - Parameters: |
| /// - start: A valid index of the collection. |
| /// - end: Another valid index of the collection. If `end` is equal to |
| /// `start`, the result is zero. |
| /// - Returns: The distance between `start` and `end`. The result can be |
| /// negative only if the collection conforms to the |
| /// `BidirectionalCollection` protocol. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the |
| /// resulting distance. |
| @inlinable |
| public func distance(from start: Index, to end: Index) -> Int { |
| _precondition(start <= end, |
| "Only BidirectionalCollections can have end come before start") |
| |
| var start = start |
| var count = 0 |
| while start != end { |
| count = count + 1 |
| formIndex(after: &start) |
| } |
| return count |
| } |
| |
| /// Returns a random element of the collection, using the given generator as |
| /// a source for randomness. |
| /// |
| /// Call `randomElement(using:)` to select a random element from an array or |
| /// another collection when you are using a custom random number generator. |
| /// This example picks a name at random from an array: |
| /// |
| /// let names = ["Zoey", "Chloe", "Amani", "Amaia"] |
| /// let randomName = names.randomElement(using: &myGenerator)! |
| /// // randomName == "Amani" |
| /// |
| /// - Parameter generator: The random number generator to use when choosing a |
| /// random element. |
| /// - Returns: A random element from the collection. If the collection is |
| /// empty, the method returns `nil`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length |
| /// of the collection. |
| /// - Note: The algorithm used to select a random element may change in a |
| /// future version of Swift. If you're passing a generator that results in |
| /// the same sequence of elements each time you run your program, that |
| /// sequence may change when your program is compiled using a different |
| /// version of Swift. |
| @inlinable |
| public func randomElement<T: RandomNumberGenerator>( |
| using generator: inout T |
| ) -> Element? { |
| guard !isEmpty else { return nil } |
| let random = Int.random(in: 0 ..< count, using: &generator) |
| let idx = index(startIndex, offsetBy: random) |
| return self[idx] |
| } |
| |
| /// Returns a random element of the collection. |
| /// |
| /// Call `randomElement()` to select a random element from an array or |
| /// another collection. This example picks a name at random from an array: |
| /// |
| /// let names = ["Zoey", "Chloe", "Amani", "Amaia"] |
| /// let randomName = names.randomElement()! |
| /// // randomName == "Amani" |
| /// |
| /// This method is equivalent to calling `randomElement(using:)`, passing in |
| /// the system's default random generator. |
| /// |
| /// - Returns: A random element from the collection. If the collection is |
| /// empty, the method returns `nil`. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length |
| /// of the collection. |
| @inlinable |
| public func randomElement() -> Element? { |
| var g = SystemRandomNumberGenerator() |
| return randomElement(using: &g) |
| } |
| |
| /// Do not use this method directly; call advanced(by: n) instead. |
| @inlinable |
| @inline(__always) |
| internal func _advanceForward(_ i: Index, by n: Int) -> Index { |
| _precondition(n >= 0, |
| "Only BidirectionalCollections can be advanced by a negative amount") |
| |
| var i = i |
| for _ in stride(from: 0, to: n, by: 1) { |
| formIndex(after: &i) |
| } |
| return i |
| } |
| |
| /// Do not use this method directly; call advanced(by: n, limit) instead. |
| @inlinable |
| @inline(__always) |
| internal func _advanceForward( |
| _ i: Index, by n: Int, limitedBy limit: Index |
| ) -> Index? { |
| _precondition(n >= 0, |
| "Only BidirectionalCollections can be advanced by a negative amount") |
| |
| var i = i |
| for _ in stride(from: 0, to: n, by: 1) { |
| if i == limit { |
| return nil |
| } |
| formIndex(after: &i) |
| } |
| return i |
| } |
| } |
| |
| /// Supply the default `makeIterator()` method for `Collection` models |
| /// that accept the default associated `Iterator`, |
| /// `IndexingIterator<Self>`. |
| extension Collection where Iterator == IndexingIterator<Self> { |
| /// Returns an iterator over the elements of the collection. |
| @inlinable // trivial-implementation |
| @inline(__always) |
| public __consuming func makeIterator() -> IndexingIterator<Self> { |
| return IndexingIterator(_elements: self) |
| } |
| } |
| |
| /// Supply the default "slicing" `subscript` for `Collection` models |
| /// that accept the default associated `SubSequence`, `Slice<Self>`. |
| extension Collection where SubSequence == Slice<Self> { |
| /// Accesses a contiguous subrange of the collection's elements. |
| /// |
| /// The accessed slice uses the same indices for the same elements as the |
| /// original collection. Always use the slice's `startIndex` property |
| /// instead of assuming that its indices start at a particular value. |
| /// |
| /// This example demonstrates getting a slice of an array of strings, finding |
| /// the index of one of the strings in the slice, and then using that index |
| /// in the original array. |
| /// |
| /// let streets = ["Adams", "Bryant", "Channing", "Douglas", "Evarts"] |
| /// let streetsSlice = streets[2 ..< streets.endIndex] |
| /// print(streetsSlice) |
| /// // Prints "["Channing", "Douglas", "Evarts"]" |
| /// |
| /// let index = streetsSlice.firstIndex(of: "Evarts") // 4 |
| /// print(streets[index!]) |
| /// // Prints "Evarts" |
| /// |
| /// - Parameter bounds: A range of the collection's indices. The bounds of |
| /// the range must be valid indices of the collection. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public subscript(bounds: Range<Index>) -> Slice<Self> { |
| _failEarlyRangeCheck(bounds, bounds: startIndex..<endIndex) |
| return Slice(base: self, bounds: bounds) |
| } |
| } |
| |
| extension Collection where SubSequence == Self { |
| /// Removes and returns the first element of the collection. |
| /// |
| /// - Returns: The first element of the collection if the collection is |
| /// not empty; otherwise, `nil`. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public mutating func popFirst() -> Element? { |
| // TODO: swift-3-indexing-model - review the following |
| guard !isEmpty else { return nil } |
| let element = first! |
| self = self[index(after: startIndex)..<endIndex] |
| return element |
| } |
| } |
| |
| /// Default implementations of core requirements |
| extension Collection { |
| /// A Boolean value indicating whether the collection is empty. |
| /// |
| /// When you need to check whether your collection is empty, use the |
| /// `isEmpty` property instead of checking that the `count` property is |
| /// equal to zero. For collections that don't conform to |
| /// `RandomAccessCollection`, accessing the `count` property iterates |
| /// through the elements of the collection. |
| /// |
| /// let horseName = "Silver" |
| /// if horseName.isEmpty { |
| /// print("I've been through the desert on a horse with no name.") |
| /// } else { |
| /// print("Hi ho, \(horseName)!") |
| /// } |
| /// // Prints "Hi ho, Silver!") |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public var isEmpty: Bool { |
| return startIndex == endIndex |
| } |
| |
| /// The first element of the collection. |
| /// |
| /// If the collection is empty, the value of this property is `nil`. |
| /// |
| /// let numbers = [10, 20, 30, 40, 50] |
| /// if let firstNumber = numbers.first { |
| /// print(firstNumber) |
| /// } |
| /// // Prints "10" |
| @inlinable |
| public var first: Element? { |
| let start = startIndex |
| if start != endIndex { return self[start] } |
| else { return nil } |
| } |
| |
| /// A value less than or equal to the number of elements in the collection. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length |
| /// of the collection. |
| @inlinable |
| public var underestimatedCount: Int { |
| // TODO: swift-3-indexing-model - review the following |
| return count |
| } |
| |
| /// The number of elements in the collection. |
| /// |
| /// To check whether a collection is empty, use its `isEmpty` property |
| /// instead of comparing `count` to zero. Unless the collection guarantees |
| /// random-access performance, calculating `count` can be an O(*n*) |
| /// operation. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length |
| /// of the collection. |
| @inlinable |
| public var count: Int { |
| return distance(from: startIndex, to: endIndex) |
| } |
| |
| // TODO: swift-3-indexing-model - rename the following to _customIndexOfEquatable(element)? |
| /// Customization point for `Collection.firstIndex(of:)`. |
| /// |
| /// Define this method if the collection can find an element in less than |
| /// O(*n*) by exploiting collection-specific knowledge. |
| /// |
| /// - Returns: `nil` if a linear search should be attempted instead, |
| /// `Optional(nil)` if the element was not found, or |
| /// `Optional(Optional(index))` if an element was found. |
| /// |
| /// - Complexity: Hopefully less than O(`count`). |
| @inlinable |
| @inline(__always) |
| public // dispatching |
| func _customIndexOfEquatableElement(_: Element) -> Index?? { |
| return nil |
| } |
| |
| /// Customization point for `Collection.lastIndex(of:)`. |
| /// |
| /// Define this method if the collection can find an element in less than |
| /// O(*n*) by exploiting collection-specific knowledge. |
| /// |
| /// - Returns: `nil` if a linear search should be attempted instead, |
| /// `Optional(nil)` if the element was not found, or |
| /// `Optional(Optional(index))` if an element was found. |
| /// |
| /// - Complexity: Hopefully less than O(`count`). |
| @inlinable |
| @inline(__always) |
| public // dispatching |
| func _customLastIndexOfEquatableElement(_ element: Element) -> Index?? { |
| return nil |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Default implementations for Collection |
| //===----------------------------------------------------------------------===// |
| |
| extension Collection { |
| /// Returns an array containing the results of mapping the given closure |
| /// over the sequence's elements. |
| /// |
| /// In this example, `map` is used first to convert the names in the array |
| /// to lowercase strings and then to count their characters. |
| /// |
| /// let cast = ["Vivien", "Marlon", "Kim", "Karl"] |
| /// let lowercaseNames = cast.map { $0.lowercased() } |
| /// // 'lowercaseNames' == ["vivien", "marlon", "kim", "karl"] |
| /// let letterCounts = cast.map { $0.count } |
| /// // 'letterCounts' == [6, 6, 3, 4] |
| /// |
| /// - Parameter transform: A mapping closure. `transform` accepts an |
| /// element of this sequence as its parameter and returns a transformed |
| /// value of the same or of a different type. |
| /// - Returns: An array containing the transformed elements of this |
| /// sequence. |
| @inlinable |
| public func map<T>( |
| _ transform: (Element) throws -> T |
| ) rethrows -> [T] { |
| // TODO: swift-3-indexing-model - review the following |
| let n = self.count |
| if n == 0 { |
| return [] |
| } |
| |
| var result = ContiguousArray<T>() |
| result.reserveCapacity(n) |
| |
| var i = self.startIndex |
| |
| for _ in 0..<n { |
| result.append(try transform(self[i])) |
| formIndex(after: &i) |
| } |
| |
| _expectEnd(of: self, is: i) |
| return Array(result) |
| } |
| |
| /// Returns a subsequence containing all but the given number of initial |
| /// elements. |
| /// |
| /// If the number of elements to drop exceeds the number of elements in |
| /// the collection, the result is an empty subsequence. |
| /// |
| /// let numbers = [1, 2, 3, 4, 5] |
| /// print(numbers.dropFirst(2)) |
| /// // Prints "[3, 4, 5]" |
| /// print(numbers.dropFirst(10)) |
| /// // Prints "[]" |
| /// |
| /// - Parameter k: The number of elements to drop from the beginning of |
| /// the collection. `k` must be greater than or equal to zero. |
| /// - Returns: A subsequence starting after the specified number of |
| /// elements. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the number of |
| /// elements to drop from the beginning of the collection. |
| @inlinable |
| public __consuming func dropFirst(_ k: Int = 1) -> SubSequence { |
| _precondition(k >= 0, "Can't drop a negative number of elements from a collection") |
| let start = index(startIndex, offsetBy: k, limitedBy: endIndex) ?? endIndex |
| return self[start..<endIndex] |
| } |
| |
| /// Returns a subsequence containing all but the specified number of final |
| /// elements. |
| /// |
| /// If the number of elements to drop exceeds the number of elements in the |
| /// collection, the result is an empty subsequence. |
| /// |
| /// let numbers = [1, 2, 3, 4, 5] |
| /// print(numbers.dropLast(2)) |
| /// // Prints "[1, 2, 3]" |
| /// print(numbers.dropLast(10)) |
| /// // Prints "[]" |
| /// |
| /// - Parameter k: The number of elements to drop off the end of the |
| /// collection. `k` must be greater than or equal to zero. |
| /// - Returns: A subsequence that leaves off the specified number of elements |
| /// at the end. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length of |
| /// the collection. |
| @inlinable |
| public __consuming func dropLast(_ k: Int = 1) -> SubSequence { |
| _precondition( |
| k >= 0, "Can't drop a negative number of elements from a collection") |
| let amount = Swift.max(0, count - k) |
| let end = index(startIndex, |
| offsetBy: amount, limitedBy: endIndex) ?? endIndex |
| return self[startIndex..<end] |
| } |
| |
| /// Returns a subsequence by skipping elements while `predicate` returns |
| /// `true` and returning the remaining elements. |
| /// |
| /// - Parameter predicate: A closure that takes an element of the |
| /// sequence as its argument and returns `true` if the element should |
| /// be skipped or `false` if it should be included. Once the predicate |
| /// returns `false` it will not be called again. |
| /// |
| /// - Complexity: O(*n*), where *n* is the length of the collection. |
| @inlinable |
| public __consuming func drop( |
| while predicate: (Element) throws -> Bool |
| ) rethrows -> SubSequence { |
| var start = startIndex |
| while try start != endIndex && predicate(self[start]) { |
| formIndex(after: &start) |
| } |
| return self[start..<endIndex] |
| } |
| |
| /// Returns a subsequence, up to the specified maximum length, containing |
| /// the initial elements of the collection. |
| /// |
| /// If the maximum length exceeds the number of elements in the collection, |
| /// the result contains all the elements in the collection. |
| /// |
| /// let numbers = [1, 2, 3, 4, 5] |
| /// print(numbers.prefix(2)) |
| /// // Prints "[1, 2]" |
| /// print(numbers.prefix(10)) |
| /// // Prints "[1, 2, 3, 4, 5]" |
| /// |
| /// - Parameter maxLength: The maximum number of elements to return. |
| /// `maxLength` must be greater than or equal to zero. |
| /// - Returns: A subsequence starting at the beginning of this collection |
| /// with at most `maxLength` elements. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the number of |
| /// elements to select from the beginning of the collection. |
| @inlinable |
| public __consuming func prefix(_ maxLength: Int) -> SubSequence { |
| _precondition( |
| maxLength >= 0, |
| "Can't take a prefix of negative length from a collection") |
| let end = index(startIndex, |
| offsetBy: maxLength, limitedBy: endIndex) ?? endIndex |
| return self[startIndex..<end] |
| } |
| |
| /// Returns a subsequence containing the initial elements until `predicate` |
| /// returns `false` and skipping the remaining elements. |
| /// |
| /// - Parameter predicate: A closure that takes an element of the |
| /// sequence as its argument and returns `true` if the element should |
| /// be included or `false` if it should be excluded. Once the predicate |
| /// returns `false` it will not be called again. |
| /// |
| /// - Complexity: O(*n*), where *n* is the length of the collection. |
| @inlinable |
| public __consuming func prefix( |
| while predicate: (Element) throws -> Bool |
| ) rethrows -> SubSequence { |
| var end = startIndex |
| while try end != endIndex && predicate(self[end]) { |
| formIndex(after: &end) |
| } |
| return self[startIndex..<end] |
| } |
| |
| /// Returns a subsequence, up to the given maximum length, containing the |
| /// final elements of the collection. |
| /// |
| /// If the maximum length exceeds the number of elements in the collection, |
| /// the result contains all the elements in the collection. |
| /// |
| /// let numbers = [1, 2, 3, 4, 5] |
| /// print(numbers.suffix(2)) |
| /// // Prints "[4, 5]" |
| /// print(numbers.suffix(10)) |
| /// // Prints "[1, 2, 3, 4, 5]" |
| /// |
| /// - Parameter maxLength: The maximum number of elements to return. The |
| /// value of `maxLength` must be greater than or equal to zero. |
| /// - Returns: A subsequence terminating at the end of the collection with at |
| /// most `maxLength` elements. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*n*), where *n* is the length of |
| /// the collection. |
| @inlinable |
| public __consuming func suffix(_ maxLength: Int) -> SubSequence { |
| _precondition( |
| maxLength >= 0, |
| "Can't take a suffix of negative length from a collection") |
| let amount = Swift.max(0, count - maxLength) |
| let start = index(startIndex, |
| offsetBy: amount, limitedBy: endIndex) ?? endIndex |
| return self[start..<endIndex] |
| } |
| |
| /// Returns a subsequence from the start of the collection up to, but not |
| /// including, the specified position. |
| /// |
| /// The resulting subsequence *does not include* the element at the position |
| /// `end`. The following example searches for the index of the number `40` |
| /// in an array of integers, and then prints the prefix of the array up to, |
| /// but not including, that index: |
| /// |
| /// let numbers = [10, 20, 30, 40, 50, 60] |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers.prefix(upTo: i)) |
| /// } |
| /// // Prints "[10, 20, 30]" |
| /// |
| /// Passing the collection's starting index as the `end` parameter results in |
| /// an empty subsequence. |
| /// |
| /// print(numbers.prefix(upTo: numbers.startIndex)) |
| /// // Prints "[]" |
| /// |
| /// Using the `prefix(upTo:)` method is equivalent to using a partial |
| /// half-open range as the collection's subscript. The subscript notation is |
| /// preferred over `prefix(upTo:)`. |
| /// |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers[..<i]) |
| /// } |
| /// // Prints "[10, 20, 30]" |
| /// |
| /// - Parameter end: The "past the end" index of the resulting subsequence. |
| /// `end` must be a valid index of the collection. |
| /// - Returns: A subsequence up to, but not including, the `end` position. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public __consuming func prefix(upTo end: Index) -> SubSequence { |
| return self[startIndex..<end] |
| } |
| |
| /// Returns a subsequence from the specified position to the end of the |
| /// collection. |
| /// |
| /// The following example searches for the index of the number `40` in an |
| /// array of integers, and then prints the suffix of the array starting at |
| /// that index: |
| /// |
| /// let numbers = [10, 20, 30, 40, 50, 60] |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers.suffix(from: i)) |
| /// } |
| /// // Prints "[40, 50, 60]" |
| /// |
| /// Passing the collection's `endIndex` as the `start` parameter results in |
| /// an empty subsequence. |
| /// |
| /// print(numbers.suffix(from: numbers.endIndex)) |
| /// // Prints "[]" |
| /// |
| /// Using the `suffix(from:)` method is equivalent to using a partial range |
| /// from the index as the collection's subscript. The subscript notation is |
| /// preferred over `suffix(from:)`. |
| /// |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers[i...]) |
| /// } |
| /// // Prints "[40, 50, 60]" |
| /// |
| /// - Parameter start: The index at which to start the resulting subsequence. |
| /// `start` must be a valid index of the collection. |
| /// - Returns: A subsequence starting at the `start` position. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public __consuming func suffix(from start: Index) -> SubSequence { |
| return self[start..<endIndex] |
| } |
| |
| /// Returns a subsequence from the start of the collection through the |
| /// specified position. |
| /// |
| /// The resulting subsequence *includes* the element at the position `end`. |
| /// The following example searches for the index of the number `40` in an |
| /// array of integers, and then prints the prefix of the array up to, and |
| /// including, that index: |
| /// |
| /// let numbers = [10, 20, 30, 40, 50, 60] |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers.prefix(through: i)) |
| /// } |
| /// // Prints "[10, 20, 30, 40]" |
| /// |
| /// Using the `prefix(through:)` method is equivalent to using a partial |
| /// closed range as the collection's subscript. The subscript notation is |
| /// preferred over `prefix(through:)`. |
| /// |
| /// if let i = numbers.firstIndex(of: 40) { |
| /// print(numbers[...i]) |
| /// } |
| /// // Prints "[10, 20, 30, 40]" |
| /// |
| /// - Parameter end: The index of the last element to include in the |
| /// resulting subsequence. `end` must be a valid index of the collection |
| /// that is not equal to the `endIndex` property. |
| /// - Returns: A subsequence up to, and including, the `end` position. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| public __consuming func prefix(through position: Index) -> SubSequence { |
| return prefix(upTo: index(after: position)) |
| } |
| |
| /// Returns the longest possible subsequences of the collection, in order, |
| /// that don't contain elements satisfying the given predicate. |
| /// |
| /// The resulting array consists of at most `maxSplits + 1` subsequences. |
| /// Elements that are used to split the sequence are not returned as part of |
| /// any subsequence. |
| /// |
| /// The following examples show the effects of the `maxSplits` and |
| /// `omittingEmptySubsequences` parameters when splitting a string using a |
| /// closure that matches spaces. The first use of `split` returns each word |
| /// that was originally separated by one or more spaces. |
| /// |
| /// let line = "BLANCHE: I don't want realism. I want magic!" |
| /// print(line.split(whereSeparator: { $0 == " " })) |
| /// // Prints "["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]" |
| /// |
| /// The second example passes `1` for the `maxSplits` parameter, so the |
| /// original string is split just once, into two new strings. |
| /// |
| /// print(line.split(maxSplits: 1, whereSeparator: { $0 == " " })) |
| /// // Prints "["BLANCHE:", " I don\'t want realism. I want magic!"]" |
| /// |
| /// The final example passes `false` for the `omittingEmptySubsequences` |
| /// parameter, so the returned array contains empty strings where spaces |
| /// were repeated. |
| /// |
| /// print(line.split(omittingEmptySubsequences: false, whereSeparator: { $0 == " " })) |
| /// // Prints "["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]" |
| /// |
| /// - Parameters: |
| /// - maxSplits: The maximum number of times to split the collection, or |
| /// one less than the number of subsequences to return. If |
| /// `maxSplits + 1` subsequences are returned, the last one is a suffix |
| /// of the original collection containing the remaining elements. |
| /// `maxSplits` must be greater than or equal to zero. The default value |
| /// is `Int.max`. |
| /// - omittingEmptySubsequences: If `false`, an empty subsequence is |
| /// returned in the result for each pair of consecutive elements |
| /// satisfying the `isSeparator` predicate and for each element at the |
| /// start or end of the collection satisfying the `isSeparator` |
| /// predicate. The default value is `true`. |
| /// - isSeparator: A closure that takes an element as an argument and |
| /// returns a Boolean value indicating whether the collection should be |
| /// split at that element. |
| /// - Returns: An array of subsequences, split from this collection's |
| /// elements. |
| /// |
| /// - Complexity: O(*n*), where *n* is the length of the collection. |
| @inlinable |
| public __consuming func split( |
| maxSplits: Int = Int.max, |
| omittingEmptySubsequences: Bool = true, |
| whereSeparator isSeparator: (Element) throws -> Bool |
| ) rethrows -> [SubSequence] { |
| // TODO: swift-3-indexing-model - review the following |
| _precondition(maxSplits >= 0, "Must take zero or more splits") |
| |
| var result: [SubSequence] = [] |
| var subSequenceStart: Index = startIndex |
| |
| func appendSubsequence(end: Index) -> Bool { |
| if subSequenceStart == end && omittingEmptySubsequences { |
| return false |
| } |
| result.append(self[subSequenceStart..<end]) |
| return true |
| } |
| |
| if maxSplits == 0 || isEmpty { |
| _ = appendSubsequence(end: endIndex) |
| return result |
| } |
| |
| var subSequenceEnd = subSequenceStart |
| let cachedEndIndex = endIndex |
| while subSequenceEnd != cachedEndIndex { |
| if try isSeparator(self[subSequenceEnd]) { |
| let didAppend = appendSubsequence(end: subSequenceEnd) |
| formIndex(after: &subSequenceEnd) |
| subSequenceStart = subSequenceEnd |
| if didAppend && result.count == maxSplits { |
| break |
| } |
| continue |
| } |
| formIndex(after: &subSequenceEnd) |
| } |
| |
| if subSequenceStart != cachedEndIndex || !omittingEmptySubsequences { |
| result.append(self[subSequenceStart..<cachedEndIndex]) |
| } |
| |
| return result |
| } |
| } |
| |
| extension Collection where Element : Equatable { |
| /// Returns the longest possible subsequences of the collection, in order, |
| /// around elements equal to the given element. |
| /// |
| /// The resulting array consists of at most `maxSplits + 1` subsequences. |
| /// Elements that are used to split the collection are not returned as part |
| /// of any subsequence. |
| /// |
| /// The following examples show the effects of the `maxSplits` and |
| /// `omittingEmptySubsequences` parameters when splitting a string at each |
| /// space character (" "). The first use of `split` returns each word that |
| /// was originally separated by one or more spaces. |
| /// |
| /// let line = "BLANCHE: I don't want realism. I want magic!" |
| /// print(line.split(separator: " ")) |
| /// // Prints "["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]" |
| /// |
| /// The second example passes `1` for the `maxSplits` parameter, so the |
| /// original string is split just once, into two new strings. |
| /// |
| /// print(line.split(separator: " ", maxSplits: 1)) |
| /// // Prints "["BLANCHE:", " I don\'t want realism. I want magic!"]" |
| /// |
| /// The final example passes `false` for the `omittingEmptySubsequences` |
| /// parameter, so the returned array contains empty strings where spaces |
| /// were repeated. |
| /// |
| /// print(line.split(separator: " ", omittingEmptySubsequences: false)) |
| /// // Prints "["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]" |
| /// |
| /// - Parameters: |
| /// - separator: The element that should be split upon. |
| /// - maxSplits: The maximum number of times to split the collection, or |
| /// one less than the number of subsequences to return. If |
| /// `maxSplits + 1` subsequences are returned, the last one is a suffix |
| /// of the original collection containing the remaining elements. |
| /// `maxSplits` must be greater than or equal to zero. The default value |
| /// is `Int.max`. |
| /// - omittingEmptySubsequences: If `false`, an empty subsequence is |
| /// returned in the result for each consecutive pair of `separator` |
| /// elements in the collection and for each instance of `separator` at |
| /// the start or end of the collection. If `true`, only nonempty |
| /// subsequences are returned. The default value is `true`. |
| /// - Returns: An array of subsequences, split from this collection's |
| /// elements. |
| /// |
| /// - Complexity: O(*n*), where *n* is the length of the collection. |
| @inlinable |
| public __consuming func split( |
| separator: Element, |
| maxSplits: Int = Int.max, |
| omittingEmptySubsequences: Bool = true |
| ) -> [SubSequence] { |
| // TODO: swift-3-indexing-model - review the following |
| return split( |
| maxSplits: maxSplits, |
| omittingEmptySubsequences: omittingEmptySubsequences, |
| whereSeparator: { $0 == separator }) |
| } |
| } |
| |
| extension Collection where SubSequence == Self { |
| /// Removes and returns the first element of the collection. |
| /// |
| /// The collection must not be empty. |
| /// |
| /// - Returns: The first element of the collection. |
| /// |
| /// - Complexity: O(1) |
| @inlinable |
| @discardableResult |
| public mutating func removeFirst() -> Element { |
| // TODO: swift-3-indexing-model - review the following |
| _precondition(!isEmpty, "Can't remove items from an empty collection") |
| let element = first! |
| self = self[index(after: startIndex)..<endIndex] |
| return element |
| } |
| |
| /// Removes the specified number of elements from the beginning of the |
| /// collection. |
| /// |
| /// - Parameter k: The number of elements to remove. `k` must be greater than |
| /// or equal to zero, and must be less than or equal to the number of |
| /// elements in the collection. |
| /// |
| /// - Complexity: O(1) if the collection conforms to |
| /// `RandomAccessCollection`; otherwise, O(*k*), where *k* is the specified |
| /// number of elements. |
| @inlinable |
| public mutating func removeFirst(_ k: Int) { |
| if k == 0 { return } |
| _precondition(k >= 0, "Number of elements to remove should be non-negative") |
| _precondition(count >= k, |
| "Can't remove more items from a collection than it contains") |
| self = self[index(startIndex, offsetBy: k)..<endIndex] |
| } |
| } |