Wouldn't this demonstration be far more useful and effective if you returned an optional Int? in the function?

Question

It seems that a far more practical and understandable way of presenting optionals here is to return an optional Int (Int?)

A bool is naturally true or false. However, returning, for example, the number of times that it can be divided would be both clearer and more useful.

For example:

func isDivisible(dividend:Int, #divisor Int) -> Int? {
  if dividend % divisor == 0 { return dividend / divisor }
  else return nil
}

if let result = isDivisible(10, divisor:2){
  println("Divisible \(result) times")
} 
else {
  println("Does not divide evenly")
}

Note: I may not name the function isDivisible in this case, mind you.

Although you example is correct, an optional int on a function named isDivisible makes less sense than just returning true or false on a standard Bool.

Great course, btw. Nice pace, easy to understand and good intro to the language.

Also, isn't apple recommending that named parameters usually start with the second parameter, unless the purpose is not clear?

Answer 1 · 2014-10-17T20:34:40Z

October 17, 2014 8:34pm

I completely agree. A function isDivisible() should only return true or false:

func isDivisible(dividend: Int, dividedBy divisor: Int) -> Bool {
    return dividend % divisor == 0
}

isDivisible(21, dividedBy: 7)    // => true 
isDivisible(22, dividedBy: 7)    // => false

Why would one ever want to return nil instead of false? And since we don't have to deal with nil here in the first place the use case for an Optional does not exist anymore.

As you proposed, an Optional would be much more useful when you want to return the quotient if the dividend is evenly divisible by the divisor or nil otherwise:

func quotient(dividend: Int, dividedBy devisor: Int) -> Int? {
    return dividend % devisor == 0 ? dividend / devisor : nil
}

quotient(21, dividedBy: 7)    // => {Some 3}
quotient(22, dividedBy: 7)    // => nil

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Matthew Stroh

Matthew Stroh

Wouldn't this demonstration be far more useful and effective if you returned an optional Int? in the function?

1 Answer

Sebastian Röder

Sebastian Röder