“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
I have found a solution. It is quite… unsatisfying, but it works. Where I set the array on the destination view controller I do: destinationViewController.options = options.map({$0 as Option})
This is my attempt: protocol ExampleProtocol { var simpleDescription: String { get } mutating func adjust() } enum ExampleEnum : ExampleProtocol { case Base, Adjusted var simpleDescription: String { return self.getDescription() } func getDescription() -> String { switch self { case .Base: return “A simple description of enum” case .Adjusted: return “Adjusted description of enum” … Read more
In Swift 4 it is now possible to declare a variable that is a subclass of a type and implements one or more protocols at the same time. var myVariable: MyClass & MyProtocol & MySecondProtocol To do an optional variable: var myVariable: (MyClass & MyProtocol & MySecondProtocol)? or as the parameter of a method: func … Read more
You have two options: 1. Use a Protocol Define the superclass as a Protocol instead of a Class Pro: Compile time check for if each “subclass” (not an actual subclass) implements the required method(s) Con: The “superclass” (protocol) cannot implement methods or properties 2. Assert in the super version of the method Example: class SuperClass … Read more
While I think I can answer your question, it’s not an answer you will like. TL;DR: @objc functions may not currently be in protocol extensions. You could create a base class instead, though that’s not an ideal solution. Protocol Extensions and Objective-C First, this question/answer (Can Swift Method Defined on Extensions on Protocols Accessed in … Read more
Protocol Observing inherits from protocol Hashable, which in turn inherits from protocol Equatable. Protocol Equatable has the following requirement: func ==(lhs: Self, rhs: Self) -> Bool And a protocol that contains Self somewhere inside it cannot be used anywhere except in a type constraint. Here is a similar question.
Why don’t protocols conform to themselves? Allowing protocols to conform to themselves in the general case is unsound. The problem lies with static protocol requirements. These include: static methods and properties Initialisers Associated types (although these currently prevent the use of a protocol as an actual type) We can access these requirements on a generic … Read more
You’ve hit a variant of a problem with protocols in Swift for which no good solution exists yet. See also Extending Array to check if it is sorted in Swift?, it contains suggestions on how to work around it that may be suitable for your specific problem (your question is very generic, maybe you can … Read more