testGenerics.swift

import UIKit

protocol Printable {
    
    func printMe()
}

class PFObject:Printable {}

class PFDictionary:Printable {
    var data:[String:Any] = [:]
}

extension Printable where Self: PFObject {
    
    func printMe() {
        print(self)
    }
}

extension Printable where Self: PFDictionary {
    
    func printMe() {
        print(data["autore"])
    }
}

func myGenericFunc<T:Printable>(objs: [T]) {

    objs.forEach { (object) in
       object.printMe()
    }
}


let pfObject = PFObject()
let pfDictionary = PFDictionary()

pfDictionary.data["autore"] = "Pippo Baudo"

let objsA: [PFObject] = [pfObject]
let objsB: [PFDictionary] = [pfDictionary]



myGenericFunc(objs: objsA)
myGenericFunc(objs: objsB)