Nice question. Here is my humble point of view: Is there a point to declaring a static function on a protocol? Pretty much the same as having instance methods declared in a protocol. The client using the protocol has to call the function on a type conforming to the protocol anyway right? Yes, exactly like … Read more
That syntax is: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Protocols.html#//apple_ref/doc/uid/TP40014097-CH25-ID521 Consider: protocol Meh { func doSomething() } // Extend protocol Meh, where `Self` is of type `UIViewController` // func blah() will only exist for classes that inherit `UIViewController`. // In fact, this entire extension only exists for `UIViewController` subclasses. extension Meh where Self: UIViewController { func blah() { print(“Blah”) } func … Read more
There’s no real reason why this shouldn’t be possible, a read-only property requirement can be covariant, as returning a ConformsToB instance from a property typed as ProtocolB is perfectly legal. Swift just currently doesn’t support it. In order to do so, the compiler would have to generate a thunk between the protocol witness table and … Read more
The problem is that, in the protocol you mark the function as mutating, which you need to do if you want to use the protocol on a struct. However, the self that is passed to testFunc is immutable (it’s a reference to a instance of the class) and that is tripping up the compiler. This … Read more
Swift 4 version AnyObject added to a protocol definition like this protocol FilterViewControllerDelegate: AnyObject { func didSearch(parameters:[String: String]?) } means that only a class will be able to conform to that protocol. So given this protocol FilterViewControllerDelegate: AnyObject { func didSearch(parameters:[String: String]?) } You will be able to write this class Foo: FilterViewControllerDelegate { func … Read more
There is a way – sort of – to do what you want – kind of. There is a way, with protocols, to eliminate the type restriction and still get the result that you want, kind of, but it isn’t always pretty. Here is what I came up with as a protocol in your situation: … Read more
1. Using default implementations (preferred). protocol MyProtocol { func doSomething() } extension MyProtocol { func doSomething() { /* return a default value or just leave empty */ } } struct MyStruct: MyProtocol { /* no compile error */ } Advantages No Objective-C runtime is involved (well, no explicitly at least). This means you can conform … Read more
Yes you can. But you never put func in front of init: protocol Serialization { init(key keyValue: String, jsonValue: String) }
“A var in a protocol with only get isn’t just a let?” No. A let indicates a constant. But that is not the case here. Consider the following: protocol SomeProtocol { var someProperty: String { get } } class SomeClass : SomeProtocol { var someProperty: String = “” func cla () { someProperty = “asd” … Read more
The problem is that you’re making a promise that the compiler can’t prove you’ll keep. So you created this promise: Calling copy() will return its own type, fully initialized. But then you implemented copy() this way: func copy() -> Self { return C() } Now I’m a subclass that doesn’t override copy(). And I return … Read more