“required” Swift Initializers and Decodable
Jordan Rose (via Jesse Squires):
The initializer is
required, right? So all subclasses need to have access to it. But the implementation we provided here might not make sense for all subclasses—what ifVerySpecialSubclassOfPointdoesn’t have aninit(x:y:)initializer? Normally, the compiler checks for this situation and makes the subclass reimplement therequiredinitializer…but that only works if therequiredinitializers are all known up front. So it can’t allow this newrequiredinitializer to go by, because someone might try to call it dynamically on a subclass.[…]
requiredinitializers are like methods: they may require dynamic dispatch. That means that they get an entry in the class’s dynamic dispatch table, commonly known as its vtable. Unlike Objective-C method tables, vtables aren’t set up to have entries arbitrarily added at run time[…]
In most cases you don’t care about hypothetical subclasses or invoking
init(from:)on some dynamicPointtype. If there was a way to markinit(from:)as something that was always available on subclasses, but dynamically checked to see if it was okay, we’d be good.[…]
For more information on this I suggest checking out my write-up of some of our initialization model problems.
