# RandomAccessCollection Implementations ## Topics ### Instance Properties [`var endIndex: Int`](/documentation/CoreMedia/CMReadOnlyDataBlockBuffer/endIndex) The position one greater than the last valid subscript argument. [`var indices: Range`](/documentation/CoreMedia/CMReadOnlyDataBlockBuffer/indices) The indices that are valid for subscripting the collection, in ascending order. [`var startIndex: Int`](/documentation/CoreMedia/CMReadOnlyDataBlockBuffer/startIndex) The position of the first element. ### Subscripts [`subscript(Range) -> CMReadOnlyDataBlockBuffer`](/documentation/CoreMedia/CMReadOnlyDataBlockBuffer/subscript(_:)-759gz) Creates a new block buffer that references a subrange of this block buffer. [`subscript(CMReadOnlyDataBlockBuffer.Index) -> UInt8`](/documentation/CoreMedia/CMReadOnlyDataBlockBuffer/subscript(_:)-8htjr) Accesses the data byte at the specified position. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)