Why can I implement square in NewtonCalculator?

Question

class Calculator {

    class func squareRoot(value: Double) -> Double {
        return sqrt(value)
    }

    final class func square(value: Double) -> Double {
        return value * value
    }

}

class NewtonCalculator : Calculator {

    override class func squareRoot(value: Double) -> Double {
        var guess = 1.0
        var newGuess: Double

        while true{
            newGuess = (value/guess + guess)/2
            if(guess == newGuess){
                return guess
            }

            guess = newGuess
        }
    }
    //Why does this function work here when its marked as "final" up above?
    class func square()->Double{
        return 5+5
    }
}

As commented in code above, why does this work? In the video he says that I shouldn't be able to implement another square method.

Answer 1 · 2016-07-15T03:30:08Z

July 15, 2016 3:30am

It works because you're not overriding the same method that's on Calculator. The names of the methods are different, and they take different types in their arguments, so they're fundamentally different. Here's an example:

//For the sake of brevity, I'm using Swift's special header syntax
class Calculator{
    final class func square(value: Double) -> Double
}

class NewtonCalculator: Calculator{
    class func square() -> Double //This is legal, because it takes no parameters, but the superclass's takes a Double
    class func square(value: Int) -> Double //This is legal, because it takes an Int, but the superclass's takes a Double
    class func square(root: Double) -> Double //This is legal, because its name is square(root:), and the superclass's is square(value:)
    class func square(value: Double) -> Int //This is legal, because it returns an Int, but the superclass's returns a Double
    override class func square(value: Double) -> Double //This is illegal, because it's named the same, takes the same types of parameters, and returns the same type as the superclass, and it attempts to override the superclass's implementation, but the superclass's implementation is marked final
}

Answer 2 · 2016-07-16T16:48:41Z

July 16, 2016 4:48pm

Thank you for the response. I probably should have known that based of what I've learned so far. Anyhow, I now know why. Thanks

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David Lallone

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Why can I implement square in NewtonCalculator?

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