ProtocolSwift5.9.0
RandomAccessCollection
A collection that supports efficient random-access index traversal.
protocol RandomAccessCollection<Element> : BidirectionalCollection where Self.Indices : RandomAccessCollection, Self.SubSequence : RandomAccessCollectionRandom-access collections can move indices any distance and measure the distance between indices in O(1) time. Therefore, the fundamental difference between random-access and bidirectional collections is that operations that depend on index movement or distance measurement offer significantly improved efficiency. For example, a random-access collection’s count property is calculated in O(1) instead of requiring iteration of an entire collection.
Conforming to the RandomAccessCollection Protocol
The RandomAccessCollection protocol adds further constraints on the associated Indices and SubSequence types, but otherwise imposes no additional requirements over the BidirectionalCollection protocol. However, in order to meet the complexity guarantees of a random-access collection, either the index for your custom type must conform to the Strideable protocol or you must implement the index(_:offsetBy:) and distance(from:to:) methods with O(1) efficiency.
Supertypes
protocol BidirectionalCollectionA collection that supports backward as well as forward traversal.
protocol CollectionA sequence whose elements can be traversed multiple times, nondestructively, and accessed by an indexed subscript.
protocol SequenceA type that provides sequential, iterated access to its elements.
Requirements
associatedtype Elementassociatedtype Indexassociatedtype Indicesassociatedtype SubSequencevar endIndex: Self.Indexvar indices: Self.IndicesThe indices that are valid for subscripting the collection, in ascending order.
var startIndex: Self.Indexsubscript(Range<Self.Index>) -> Self.SubSequence Accesses a contiguous subrange of the collection’s elements.
subscript(Self.Index) -> Self.Element func distance(from: Self.Index, to: Self.Index) -> Int Returns the distance between two indices.
func formIndex(after: inout Self.Index) Replaces the given index with its successor.
func formIndex(before: inout Self.Index) Replaces the given index with its predecessor.
func index(Self.Index, offsetBy: Int) -> Self.Index Returns an index that is the specified distance from the given index.
func index(Self.Index, offsetBy: Int, limitedBy: Self.Index) -> Self.Index? Returns an index that is the specified distance from the given index, unless that distance is beyond a given limiting index.
func index(after: Self.Index) -> Self.Index Returns the position immediately after the given index.
func index(before: Self.Index) -> Self.Index Returns the position immediately before the given index.