Generic protocols to map out the properties of DataSource

DataSource.swift

public protocol Generative {
    typealias GeneratedType
    
    var elements: [GeneratedType] { get }
}

public extension Generative {
    func count() -> Int {
        return elements.count
    }

    subscript(index:Int) -> GeneratedType? {
        if index >= count() {
            return nil
        }
        return elements[index]
    }

}

public protocol Selectable {
    typealias SelectableType: Hashable
    
    var selectedElements: Set<SelectableType> { get set }
    
}

extension Selectable {
    public func isSelected(elem: SelectableType) -> Bool {
        return selectedElements.contains(elem)
    }
    
    public mutating func addSelection(elem: SelectableType) {
        selectedElements.insert(elem)
    }
    
    public mutating func removeSelection(elem: SelectableType) {
        selectedElements.remove(elem)
    }
    
    public mutating func clearSelections() {
        selectedElements.removeAll()
    }
}

func selectedIndices<S: Selectable where S: Generative, S.GeneratedType == S.SelectableType>(ds: S) -> [NSIndexPath] {
    return ds.selectedElements
        .flatMap { (p: S.GeneratedType) -> NSIndexPath? in
            if let idx = ds.elements.indexOf(p) { idx
                return NSIndexPath(forRow: idx, inSection: 0)
            }
            return nil
    }
}