Class conforming to protocol as function parameter in Swift

Question

In Objective-C, it's possible to specify a class conforming to a protocol as a method parameter. For example, I could have a method that only allows a UIViewController that conforms to UITableViewDataSource:

- (void)foo:(UIViewController<UITableViewDataSource> *)vc; 

I can't find a way to do this in Swift (perhaps it's not possible yet). You can specify multiple protocols using func foo(obj: protocol<P1, P2>), but how do you require that the object is of a particular class as well?

Answer 1

You can define foo as a generic function and use type constraints to require both a class and a protocol.

Swift 4

func foo<T: UIViewController & UITableViewDataSource>(vc: T) {     ..... } 

Swift 3 (works for Swift 4 also)

func foo<T: UIViewController>(vc:T) where T:UITableViewDataSource {      .... } 

Swift 2

func foo<T: UIViewController where T: UITableViewDataSource>(vc: T) {     // access UIViewController property     let view = vc.view     // call UITableViewDataSource method     let sections = vc.numberOfSectionsInTableView?(tableView) } 

Answer 2

In Swift 4 you can achieve this with the new & sign:

let vc: UIViewController & UITableViewDataSource