SE-0068 expands Swift’s use of Self
so that it refers to the containing type when used inside classes, structs, and enums. This is particularly useful for dynamic types, where the exact type of something needs to be determined at runtime.
As an example, consider this code:
class NetworkManager {
class var maximumActiveRequests: Int {
return 4
}
func printDebugData() {
print("Maximum network requests: \(NetworkManager.maximumActiveRequests).")
}
}
That declares a static maximumActiveRequests
property for a network manager, and adds a printDebugData()
method to print the static property. That works fine right now, but when NetworkManager
is subclassed things become more complicated:
class ThrottledNetworkManager: NetworkManager {
override class var maximumActiveRequests: Int {
return 1
}
}
That subclass changes maximumActiveRequests
so that it allows only one request at a time, but if we call printDebugData()
it will print out the value from its parent class:
let manager = ThrottledNetworkManager()
manager.printDebugData()
That should print out 1 rather than 4, and that’s where SE-0068 comes in: we can now write Self
(with a capital S) to refer to the current type. So, we can rewrite printDebugData()
to this:
class ImprovedNetworkManager {
class var maximumActiveRequests: Int {
return 4
}
func printDebugData() {
print("Maximum network requests: \(Self.maximumActiveRequests).")
}
}
This means Self
works the same way as it did for protocols in earlier Swift versions.
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