Class conforming to protocol as function parameter in Swift

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)
}