IndexingIterator
A type that iterates over a collection using its indices.
@frozen struct IndexingIterator<Elements> where Elements : CollectionThe 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"Citizens in Swift
where Elements:CollectionConformances
protocol IteratorProtocolA type that supplies the values of a sequence one at a time.
protocol SequenceA type that provides sequential, iterated access to its elements.
Members
func next() -> Elements.Element? Advances to the next element and returns it, or
nilif no next element exists.typealias Elementtypealias Iteratortypealias SubSequence
Features
var lazy: LazySequence<Self>A sequence containing the same elements as this sequence, but on which some operations, such as
mapandfilter, are implemented lazily.func allSatisfy((Self.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether every element of a sequence satisfies a given predicate.
func compactMap<ElementOfResult>((Self.Element) throws -> ElementOfResult?) rethrows -> [ElementOfResult] Returns an array containing the non-
nilresults of calling the given transformation with each element of this sequence.func contains(Self.Element) -> Bool Returns a Boolean value indicating whether the sequence contains the given element.
func contains(where: (Self.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether the sequence contains an element that satisfies the given predicate.
func drop(while: (Self.Element) throws -> Bool) rethrows -> DropWhileSequence<Self> Returns a sequence by skipping the initial, consecutive elements that satisfy the given predicate.
func dropFirst(Int) -> DropFirstSequence<Self> Returns a sequence containing all but the given number of initial elements.
func dropLast(Int) -> [Self.Element] Returns a sequence containing all but the given number of final elements.
func elementsEqual<OtherSequence>(OtherSequence) -> Bool Returns a Boolean value indicating whether this sequence and another sequence contain the same elements in the same order.
func elementsEqual<OtherSequence>(OtherSequence, by: (Self.Element, OtherSequence.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether this sequence and another sequence contain equivalent elements in the same order, using the given predicate as the equivalence test.
func enumerated() -> EnumeratedSequence<Self> Returns a sequence of pairs (n, x), where n represents a consecutive integer starting at zero and x represents an element of the sequence.
func filter((Self.Element) throws -> Bool) rethrows -> [Self.Element] Returns an array containing, in order, the elements of the sequence that satisfy the given predicate.
func first(where: (Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the first element of the sequence that satisfies the given predicate.
func flatMap<SegmentOfResult>((Self.Element) throws -> SegmentOfResult) rethrows -> [SegmentOfResult.Element] Returns an array containing the concatenated results of calling the given transformation with each element of this sequence.
func forEach((Self.Element) throws -> Void) rethrows Calls the given closure on each element in the sequence in the same order as a
for-inloop.func joined() -> FlattenSequence<Self> Returns the elements of this sequence of sequences, concatenated.
func joined<Separator>(separator: Separator) -> JoinedSequence<Self> Returns the concatenated elements of this sequence of sequences, inserting the given separator between each element.
func joined(separator: String) -> String Returns a new string by concatenating the elements of the sequence, adding the given separator between each element.
func lexicographicallyPrecedes<OtherSequence>(OtherSequence) -> Bool Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the less-than operator (
<) to compare elements.func lexicographicallyPrecedes<OtherSequence>(OtherSequence, by: (Self.Element, Self.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the given predicate to compare elements.
func map<T>((Self.Element) throws -> T) rethrows -> [T] Returns an array containing the results of mapping the given closure over the sequence’s elements.
func max() -> Self.Element? Returns the maximum element in the sequence.
func max(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the maximum element in the sequence, using the given predicate as the comparison between elements.
func min() -> Self.Element? Returns the minimum element in the sequence.
func min(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> Self.Element? Returns the minimum element in the sequence, using the given predicate as the comparison between elements.
func prefix(Int) -> PrefixSequence<Self> Returns a sequence, up to the specified maximum length, containing the initial elements of the sequence.
func prefix(while: (Self.Element) throws -> Bool) rethrows -> [Self.Element] Returns a sequence containing the initial, consecutive elements that satisfy the given predicate.
func reduce<Result>(Result, (Result, Self.Element) throws -> Result) rethrows -> Result Returns the result of combining the elements of the sequence using the given closure.
func reduce<Result>(into: Result, (inout Result, Self.Element) throws -> ()) rethrows -> Result Returns the result of combining the elements of the sequence using the given closure.
func reversed() -> [Self.Element] Returns an array containing the elements of this sequence in reverse order.
func shuffled() -> [Self.Element] Returns the elements of the sequence, shuffled.
func shuffled<T>(using: inout T) -> [Self.Element] Returns the elements of the sequence, shuffled using the given generator as a source for randomness.
func sorted() -> [Self.Element] Returns the elements of the sequence, sorted.
func sorted(by: (Self.Element, Self.Element) throws -> Bool) rethrows -> [Self.Element] Returns the elements of the sequence, sorted using the given predicate as the comparison between elements.
func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (Self.Element) throws -> Bool) rethrows -> [ArraySlice<Self.Element>] Returns the longest possible subsequences of the sequence, in order, that don’t contain elements satisfying the given predicate. Elements that are used to split the sequence are not returned as part of any subsequence.
func split(separator: Self.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [ArraySlice<Self.Element>] Returns the longest possible subsequences of the sequence, in order, around elements equal to the given element.
func starts<PossiblePrefix>(with: PossiblePrefix) -> Bool Returns a Boolean value indicating whether the initial elements of the sequence are the same as the elements in another sequence.
func starts<PossiblePrefix>(with: PossiblePrefix, by: (Self.Element, PossiblePrefix.Element) throws -> Bool) rethrows -> Bool Returns a Boolean value indicating whether the initial elements of the sequence are equivalent to the elements in another sequence, using the given predicate as the equivalence test.
func suffix(Int) -> [Self.Element] Returns a subsequence, up to the given maximum length, containing the final elements of the sequence.
func flatMap<ElementOfResult>((Self.Element) throws -> ElementOfResult?) rethrows -> [ElementOfResult]
Citizens in Swift
where Elements:Collection, Elements:Sendable, Elements.Index:SendableConformances
protocol SendableA type whose values can safely be passed across concurrency domains by copying.