public protocol QueryStringConvertible {
    
    var asQueryString: String { get }
    
}

extension Array: QueryStringConvertible where Element: QueryStringConvertible {
    
    public var asQueryString: String {
        return self.reduce("") { $0.isEmpty ? $1.asQueryString : "\($0)&\($1.asQueryString)"  }
    }
    
}

extension Dictionary: QueryStringConvertible where Key == String, Value: CustomStringConvertible {
    
    public var asQueryString: String {
        return self.reduce("") { ($0.isEmpty ? "" : "\($0)&") + "\($1.key)=\($1.value)" }
    }
    
}

struct Person: QueryStringConvertible {
    
    let firstName: String
    let lastName: String
    
    public var asQueryString: String {
        return "firstName=\(firstName)&lastName=\(lastName)"
    }
    
}

func bar<Q: QueryStringConvertible>(query: Q) -> String{
    return "QUERY: " + query.asQueryString
}

func baz(query: QueryStringConvertible) -> String {
    return "QUERY: " + query.asQueryString
}

let dictionary = [ "param1" : "value1", "param2" : "value2" ]
dictionary.asQueryString
let person = Person(firstName: "John", lastName: "Doe")
person.asQueryString
bar(query: dictionary)
bar(query: person)
bar(query: [dictionary])
bar(query: [person])

// THIS does not compile -> '<Q where Q : QueryStringConvertible> (query: Q) -> String' requires that 'Any' conform to 'QueryStringConvertible'
bar(query: [dictionary, person])

baz(query: dictionary)
baz(query: person)
baz(query: [dictionary])
baz(query: [person])

//  This does not compile -> Contextual type 'QueryStringConvertible' cannot be used with array literal
baz(query: [dictionary, person])