# Collection Implementations ## Topics ### Instance Properties [`var count: Int`](/documentation/Swift/Substring/count) The number of elements in the collection. [`var endIndex: Substring.Index`](/documentation/Swift/Substring/endIndex) The collection’s “past the end” position—that is, the position one greater than the last valid subscript argument. [`var first: Self.Element?`](/documentation/Swift/Substring/first) The first element of the collection. [`var indices: DefaultIndices`](/documentation/Swift/Substring/indices-swift.property) The indices that are valid for subscripting the collection, in ascending order. [`var isEmpty: Bool`](/documentation/Swift/Substring/isEmpty) A Boolean value indicating whether the collection is empty. [`var startIndex: Substring.Index`](/documentation/Swift/Substring/startIndex) The position of the first element in a nonempty collection. [`var underestimatedCount: Int`](/documentation/Swift/Substring/underestimatedCount) A value less than or equal to the number of elements in the collection. ### Instance Methods [`func drop(while: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence`](/documentation/Swift/Substring/drop(while:)) Returns a subsequence by skipping elements while `predicate` returns `true` and returning the remaining elements. [`func dropFirst(Int) -> Self.SubSequence`](/documentation/Swift/Substring/dropFirst(_:)) Returns a subsequence containing all but the given number of initial elements. [`func firstIndex(of: Self.Element) -> Self.Index?`](/documentation/Swift/Substring/firstIndex(of:)) Returns the first index where the specified value appears in the collection. [`func firstIndex(where: (Self.Element) throws -> Bool) rethrows -> Self.Index?`](/documentation/Swift/Substring/firstIndex(where:)) Returns the first index in which an element of the collection satisfies the given predicate. [`func formIndex(inout Self.Index, offsetBy: Int)`](/documentation/Swift/Substring/formIndex(_:offsetBy:)) Offsets the given index by the specified distance. [`func formIndex(inout Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Bool`](/documentation/Swift/Substring/formIndex(_:offsetBy:limitedBy:)) Offsets the given index by the specified distance, or so that it equals the given limiting index. [`func formIndex(after: inout Self.Index)`](/documentation/Swift/Substring/formIndex(after:)) Replaces the given index with its successor. [`func index(of: Self.Element) -> Self.Index?`](/documentation/Swift/Substring/index(of:)) Returns the first index where the specified value appears in the collection. [`func indices(of: Self.Element) -> RangeSet`](/documentation/Swift/Substring/indices(of:)) Returns the indices of all the elements that are equal to the given element. [`func indices(where: (Self.Element) throws -> Bool) rethrows -> RangeSet`](/documentation/Swift/Substring/indices(where:)) Returns the indices of all the elements that match the given predicate. [`func makeIterator() -> IndexingIterator`](/documentation/Swift/Substring/makeIterator()) Returns an iterator over the elements of the collection. [`func map((Self.Element) throws(E) -> T) throws(E) -> [T]`](/documentation/Swift/Substring/map(_:)-5p6oh) Returns an array containing the results of mapping the given closure over the sequence’s elements. [`func popFirst() -> Self.Element?`](/documentation/Swift/Substring/popFirst()) Removes and returns the first element of the collection. [`func prefix(Int) -> Self.SubSequence`](/documentation/Swift/Substring/prefix(_:)) Returns a subsequence, up to the specified maximum length, containing the initial elements of the collection. [`func prefix(through: Self.Index) -> Self.SubSequence`](/documentation/Swift/Substring/prefix(through:)) Returns a subsequence from the start of the collection through the specified position. [`func prefix(upTo: Self.Index) -> Self.SubSequence`](/documentation/Swift/Substring/prefix(upTo:)) Returns a subsequence from the start of the collection up to, but not including, the specified position. [`func prefix(while: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence`](/documentation/Swift/Substring/prefix(while:)) Returns a subsequence containing the initial elements until `predicate` returns `false` and skipping the remaining elements. [`func randomElement() -> Self.Element?`](/documentation/Swift/Substring/randomElement()) Returns a random element of the collection. [`func randomElement(using: inout T) -> Self.Element?`](/documentation/Swift/Substring/randomElement(using:)) Returns a random element of the collection, using the given generator as a source for randomness. [`func removeFirst() -> Self.Element`](/documentation/Swift/Substring/removeFirst()-5bf95) Removes and returns the first element of the collection. [`func removeFirst(Int)`](/documentation/Swift/Substring/removeFirst(_:)-5qb6j) Removes the specified number of elements from the beginning of the collection. [`func removingSubranges(RangeSet) -> DiscontiguousSlice`](/documentation/Swift/Substring/removingSubranges(_:)) Returns a collection of the elements in this collection that are not represented by the given range set. [`func split(maxSplits: Int, omittingEmptySubsequences: Bool, whereSeparator: (Self.Element) throws -> Bool) rethrows -> [Self.SubSequence]`](/documentation/Swift/Substring/split(maxSplits:omittingEmptySubsequences:whereSeparator:)) Returns the longest possible subsequences of the collection, in order, that don’t contain elements satisfying the given predicate. [`func split(separator: Self.Element, maxSplits: Int, omittingEmptySubsequences: Bool) -> [Self.SubSequence]`](/documentation/Swift/Substring/split(separator:maxSplits:omittingEmptySubsequences:)) Returns the longest possible subsequences of the collection, in order, around elements equal to the given element. [`func suffix(from: Self.Index) -> Self.SubSequence`](/documentation/Swift/Substring/suffix(from:)) Returns a subsequence from the specified position to the end of the collection. ### Subscripts [`subscript(Substring.Index) -> Character`](/documentation/Swift/Substring/subscript(_:)-2nr4p) Accesses the element at the specified position. [`subscript(RangeSet) -> DiscontiguousSlice`](/documentation/Swift/Substring/subscript(_:)-392pj) Accesses a view of this collection with the elements at the given indices. [`subscript(UnboundedRange) -> Self.SubSequence`](/documentation/Swift/Substring/subscript(_:)-4al8g) [`subscript(R) -> Self.SubSequence`](/documentation/Swift/Substring/subscript(_:)-4h7r7) Accesses the contiguous subrange of the collection’s elements specified by a range expression. ### Type Aliases [`typealias Index`](/documentation/Swift/Substring/Index) A type that represents a position in the collection. [`typealias Indices`](/documentation/Swift/Substring/Indices) A type that represents the indices that are valid for subscripting the collection, in ascending order. [`typealias Iterator`](/documentation/Swift/Substring/Iterator) A type that provides the collection’s iteration interface and encapsulates its iteration state. [`typealias SubSequence`](/documentation/Swift/Substring/SubSequence) A collection representing a contiguous subrange of this collection’s elements. The subsequence shares indices with the original collection. --- Copyright © 2026 Apple Inc. 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