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iOS Swift Functions and Optionals Optionals Exercise: isDivisible function

HaeJu Lee
HaeJu Lee
3,811 Points

Question about [Case of NOT USING "if let" syntax]

Amit used below.

if let result = isDivisible(dividend: 15, divisor: 3) { ... }

I tried to use the following,

if isDivisible(dividend:15, divisor:3) { ... }

which triggers this error message.

"optional type 'Bool?' cannot be used as a boolean; test for '!=nil' instead."

Well, I don't see the difference between

"if isDivisible(dividend:15, divisor:3)" and

"if let result = isDivisible(dividend: 15, divisor: 3)" ,

Because isDivisible(dividend:15, divisor:3) itself also returns true or nil.

Why should I introduce a new constant "result" to make my code run?

2 Answers

Jhoan Arango
Jhoan Arango
14,575 Points

Hello HaeJu Lee:

β€œYou can use if and let together to work with values that might be missing. These values are represented as optionals. An optional value either contains a value or contains nil to indicate that a value is missing. Write a question mark (?) after the type of a value to mark the value as optional.”

Excerpt From: Apple Inc. β€œThe Swift Programming Language (Swift 2 Prerelease).” iBooks. https://itun.es/us/k5SW7.l

Andrew Wertheim
Andrew Wertheim
1,649 Points

Hi Jhoan (and HaeJu Lee, and Amit)

I had a similar question. I set my code up the same way as HaeJu Lee and noticed the same error. I modified my code to test for != nil instead and my code gives the same results as Amit's example. My code is below. My question is, is there a reason that I should use if let and create a new variable as Amit does just to unwrap the optional? Or is there danger in doing it my way, bypassing creating the new variable with if let..?

My code:

if divTest(numOne: 100, numTwo: 25) != nil { println("Divisible")

} else { println("Not Divisible") }

Thanks for the help guys. This has been a great course so far!