Can I have an init func in a protocol?

Question

When I try to implement my protocol this way:

protocol Serialization {
    func init(key keyValue: String, jsonValue: String)
}

I get an error saying: Expected identifier in function declaration.

Why am I getting this error?

Why do you want this in a protocol? Why does it care how the type is created? — mmmmmm, Sep 05 '14 at 22:52
An object can have multiple init functions. Why not have one prescribed by a protocol as one that could get called? — Aaron Bratcher, Sep 06 '14 at 00:29
That's because the `func` keyword right before `init`. Remove it and try it again. — Windor C, Sep 06 '14 at 00:44

score 132 · Accepted Answer · answered Sep 06 '14 at 01:58

132

Yes you can. But you never put func in front of init:

protocol Serialization {
    init(key keyValue: String, jsonValue: String)
}

answered Sep 06 '14 at 01:58

newacct

1

Can you explain the reason for not putting func in front of init? Thanks. – LiweiZ Jan 26 '15 at 21:34
6

@LiweiZ: because initializers and methods are separate – newacct Jan 26 '15 at 21:36
1

Thank you. I guess I need to go through the developer docs one more time:) – LiweiZ Jan 27 '15 at 01:36
3

OK, Swift is known for its style consistencies, and this is very inconsistent and confusing to newbs. Thanks for the answer. – Jay Imerman Jul 21 '15 at 21:31

score 44 · Answer 2 · answered Jun 20 '15 at 19:58

Key points here:

The protocol and the class that implements it, never have the keyword func in front of the init method.
In your class, since the init method was called out in your protocol, you now need to prefix the init method with the keyword required. This indicates that a protocol you conform to required you to have this init method (even though you may have independently thought that it was a great idea).

As covered by others, your protocol would look like this:

protocol Serialization {
    init(key keyValue: String, jsonValue: String)
}

And as an example, a class that conforms to this protocol might look like so:

class Person: Serialization {
    required init(key keyValue: String, jsonValue: String) {
       // your logic here
    }
}

Notice the required keyword in front of the init method.

2 Answers2