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Gene Bogdanovich
14,618 PointsInitializing a Subclass
In the Object Oriented Swift 3 course in the lesson called Overriding Properties instructor said that when we're initializing a subclass we first need to provide values for properties of the subclass, but in the Build a Simple iPhone App with Swift 3 course in the quiz called Recap of Object Oriented Swift one of the quiz's questions says "When we initialize a subclass, we first need to initialize the properties in our base class, then call the super class' initializer". So what do we need to do first? Provide values for properties of the base class or the subclass?
Thanks for any help!
1 Answer
Chris Stromberg
Courses Plus Student 13,389 PointsThere is a good explanation of what you are asking here regarding two-phase initialization.
From the apple docs:
Swift’s compiler performs four helpful safety-checks to make sure that two-phase initialization is completed without error:
A designated initializer must ensure that all of the properties introduced by its class are initialized before it delegates >up to a superclass initializer.
As mentioned above, the memory for an object is only considered fully initialized once the initial state of all of its stored properties is known. In order for this rule to be satisfied, a designated initializer must make sure that all of its own properties are initialized before it hands off up the chain. "