Swift modifiable in properties

Question

protocol Deck {
var cards: [String] {get set} // {get mutable set}
}

struct MyDeck: Deck {   
 var cards: [String] =  (1...7).map {_ in return String(rand())}
}

Do I just need to specify {get mutable set} in the protocol? It is not possible to find any documents on why not using the mutable keyword in the setter declaration if my setter mutates my structure

Answer 1

First of all, note that the discussion keyword is , not . mutatingmutable

---

The default state setismutating

• To quickly answer your question: mutating- this is the default state for setters, and therefore you do not need to explicitly use the keyword mutatingto indicate this.

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More details

The following default behavior is performed for getter and seters:

• get nonmutating default
• set mutating default

, , ... { get set } , ( ), , nonmutating get mutating set struct,

protocol Deck {
    var cards: [String] {get set}
}

// implicitly, OK
struct MyDeckA: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        get { return ["foo"] }
        set { mutateMe += 1 }
    }
}

// explicitly, OK
struct MyDeckB: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        nonmutating get { return ["foo"] }
        mutating set { mutateMe += 1 }
    }
}

/* error, MyDeckC does not conform to Deck 
  (mutating getter, wheres a nonmutating one is blueprinted!) */
struct MyDeckC: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        mutating get { return ["foo"] }
        mutating set { mutateMe += 1 }
    }
}

, , ( , , ).

protocol Deck {
    var cards: [String] {mutating get nonmutating set}
}

/* when conforming to this non-default get/set setup blueprinted in 
   protocol Deck, we need to explicitly specify our non-default 
   (w.r.t. mutating) getter and setter */
struct MyDeckD: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        mutating get { mutateMe += 1; return ["foo"] }
        nonmutating set { print("I can't mutate self ...") }
    }
}

, , ( ) (... {get set}), , , mutating set, nonmutating

protocol Deck {
    var cards: [String] {get set}
}

struct MyDeckE: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        get { return ["foo"] }
        nonmutating set { print("I can't mutate self ...") }
            /* setter cannot mutate self */
    }
}

, , , , , , , , self. , , get mutating getter: - nonmutating one.

protocol Deck {
    var cards: [String] {mutating get set}
}

struct MyDeckF: Deck {
    var mutateMe: Int = 0
    var cards: [String] {
        nonmutating get { print("I can't mutate self ..."); return ["foo"] }
            /* getter cannot mutate self */
        set { mutateMe += 1 }
    }
}