You cannot implement a read-write property requirement of type BasePresenterProtocol? with a property of type DashboardPresenterProtocol?. Consider what would happen if this were possible, and you upcast an instance of DashboardPresenter to DashboardViewProtocol. You would be able to assign anything that conforms to BasePresenterProtocol to a property of type DashboardPresenterProtocol? – which would be illegal. … Read more
You have to define the protocol as a class protocol: protocol ValueProvider : class { var value: String {get set} } Then var value: String { get { return v.value } set { v.value = newValue } } compiles and works as expected (i.e. assigns the new value to the object referenced by v1 if … 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
The Error is correct. You have to make your class final, since no subclasses could conform your protocol Ownee. Consider this subclass: class FirstGradeStudent: Student { // Student contains following variable: // var owner: Owner<Student> { // return professor // } } As you can see, it would have to implement var owner: Owner<Student> because … 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
TL;DR The value of Self in a protocol extension is determined by a complex set of factors. It’s almost always preferable to use self at static level, or type(of: self) at instance level in place of Self. This ensures that you’re always working with the dynamic type that the method is called on, preventing weird … 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
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
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
(I realise that OP is asking less about the language implications and more about what the compiler does – but I feel it’s also worthwhile also to list the general differences between generic and protocol-typed function parameters) 1. A generic placeholder constrained by a protocol must be satisfied with a concrete type This is a … Read more