A snippet for extending a UITableViewController subclass, allowing the selection feature for ONLY one row through the Checkmark accssory.

UITableViewOnlyOneRowSelection.swift

// A snippet for extending a UITableViewController class, 
// allowing the selection of only one row through the Checkmark accssory.
// If you using a stand alone UITableView, then implement these methods in your delegate object.

// For checking which row is selected, check the indexPathForSelectedRow property of the tableView.
// This code is implemented in the latest version of Swift, which is Swift 3, as of today...

extension <#Your UITableViewController class#> {

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {       
        if let sip = selectedIndex {
            tableView.deselectRow(at: sip, animated: false)
        }
        selectedIndex = indexPath
    }
    
    override func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
        if selectedIndex?.row == indexPath.row {
            selectedIndex = nil
        }
    }
}