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Alex Kuo
7,889 PointsCode Question About Convenience Init in the Course
Hi, buddies,
I am curious about the following code from this course :
class Car: Vehicle { let numberOfDoors: Int
init(name: String, numberOfDoors: Int) self.numberOfDoors = numberOfDoors super.init(name:name)
convenience override init(name:String){ self.init(name:name,numberOfDoors:4)
convenience init(){ self.init(name:"Unnamed") }
}
}
In the last convenience init, why we do not have to specify the parameter "numberOfDoors" ? What is the "self.init" in the last convenience init ? The designated one or the convenience one preceeding the last one ?
1 Answer
Charles Kenney
15,604 PointsGood question. Convenience initializers, by design do not take all the base initializer's parameters. This is exactly why they are called convenience initializers. Their purpose is to support a specific pattern / use case of initialization with a given object, and therefore come with certain predefined properties.
With this example, our car class has the stored property 'numberOfDoors'. Because most cars have 4 doors, we can write a convenient supporting initializer, to call the designated initializer (self.init) and automatically pass 4 for the numberOfDoors parameter. Now when we want to create a car object resembling a common 4-door car, all we have to do is pass the parameter for the name. And just like that, we're writing more efficient code.
I recommend reading the initialization section of the Swift 3.1 docs.
Hope this answers your question, -Charles