Cannot assign to property in protocol - Swift compiler error

Question

I\'m banging my head against the wall with the following code in Swift. I\'ve defined a simple protocol:

protocol Nameable {
    var name : String { get set          


        

Answer 1

It's because, Nameable being a protocol, Swift doesn't know what kind (flavor) of object your function's incoming Nameable is. It might be a class instance, sure - but it might be a struct instance. And you can't assign to a property of a constant struct, as the following example demonstrates:

struct NameableStruct : Nameable {
    var name : String = ""
}
let ns = NameableStruct(name:"one")
ns.name = "two" // can't assign

Well, by default, an incoming function parameter is a constant - it is exactly as if you had said let in your function declaration before you said nameable.

The solution is to make this parameter not be a constant:

func nameNameable(var nameable: Nameable, name: String ) {
                  ^^^

NOTE Later versions of Swift have abolished the var function parameter notation, so you'd accomplish the same thing by assigning the constant to a variable:

protocol Nameable {
    var name : String { get set }
}
func nameNameable(nameable: Nameable, name: String) {
    var nameable = nameable // can't compile without this line
    nameable.name = name
}