protocol SomeProtocol {
    mutating func update()
}
struct ObjectWrapper<T: AnyObject> {
    let base: T
}

struct Example: SomeProtocol { func update() { } }

let x = ObjectWrapper(base: Example())
x.base.update()

extension ObjectWrapper where T: SomeProtocol {
    func update() {
        self.base.update()
    }
}

func update
    <S: Sequence where S.Iterator.Element: SomeProtocol, S.Iterator.Element: AnyObject>
    (sequence: S)
{
    for element in sequence {
        let wrapper = ObjectWrapper(base: element)
        wrapper.base.update()
    }
}