Annotating Swift function declarations that support conformance to a protocol? - swift

Question

Is there a standard mechanism for annotating function declarations in Swift to indicate that they are present because a class conforms to some protocol?
For instance, this declaration might be present because a class conforms to NSCoding. (Marking it with override would result in a syntax error, so it's not the kind of annotation I am looking for.) Ideally I am looking for a code-level annotation (e.g. override instead of /*! ... */).
// ... annotation such as "conform to NSCoding", if possible
func encodeWithCoder(encoder: NSCoder) {
// ...
}

Answer 1

You can use extension. for example:
protocol SomeProtocol {
func doIt() -> Int
}
class ConcreteClass {
....
}
extension ConcreteClass: SomeProtocol {
func doIt() -> Int {
// ...
return 1
}
}
But you cannot define required initializer in extension, for example:
// THIS DOES NOT WORK!!!
class Foo: NSObject {
}
extension Foo: NSCoding {
required convenience init(coder aDecoder: NSCoder) {
self.init()
}
func encodeWithCoder(aCoder: NSCoder) {
// ...
}
}
emits an error:
error: 'required' initializer must be declared directly in class 'Foo' (not in an extension)
required convenience init(coder aDecoder: NSCoder) {
~~~~~~~~ ^
In this case, you should use // MARK: comments:
class Foo: NSObject {
// ...
// MARK: NSCoding
required init(coder aDecoder: NSCoder) {
super.init()
}
func encodeWithCoder(aCoder: NSCoder) {
// ...
}
}