A collection that supports efficient random-access index traversal.
- Xcode 8.0+
- Swift Standard Library
Random-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
Random protocol adds further constraints on the associated
Sub types, but otherwise imposes no additional requirements over the
Bidirectional 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
distance(from: methods with O(1) efficiency.