Can I declare a function inside a class without body in Swift?

So I was referring to the UIKit.UITableView file and I noticed that all the functions inside UITableView class are written without their body. I tried to do the same in my project but Xcode wouldn't let me do so. Can someone explain how was that possible in the source file?

Below is a sample snippet from there.

open func insertRows(at indexPaths: [IndexPath], with animation: UITableView.RowAnimation)

open func deleteRows(at indexPaths: [IndexPath], with animation: UITableView.RowAnimation)

@available(iOS 5.0, *)
open func moveRow(at indexPath: IndexPath, to newIndexPath: IndexPath)

@available(iOS 3.0, *)
open func reloadRows(at indexPaths: [IndexPath], with animation: UITableView.RowAnimation)