Return a boolean value from a function in Swift 3.0

Question

I cannot figure how the new first label proposal for Swift 3.0 applies to returnTypes with Bool:

var firstString = "string"
var secondString = "thing"

func areTheStringsAnagrams(first: String, second: String) -> Bool {
    return first.characters.sorted() == second.characters.sorted()
}

areTheStringsAnagrams(first: firstString, second: secondString)

Why is the call to the function unused?

The error is:

/swift-execution/Sources/main.swift:11:1: warning: result of call to 'areTheStringsAnagrams(first:second:)' is unused areTheStringsAnagrams(first: firstString, second: secondString) ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Although a previous questions focused on NSLayoutConstraints (i.e., Result of call to [myFunction] is unused) in a comparison to Objective-C, the present question is narrower in that it focuses exclusively on function calls with a returnType of Bool in Swift 3.0.

This code does compile and work properly. What is this question about? — Luca Angeletti, Nov 16 '16 at 01:14
I cannot figure out what the problem with this code is. I ran it both in a Playground as well as in IBM's Swift Playground but function call is unused. I am stumped. — Eric, Nov 16 '16 at 01:15
Possible duplicate of [Result of call to \[myFunction\] is unused](http://stackoverflow.com/questions/37939573/result-of-call-to-myfunction-is-unused) — rmaddy, Nov 16 '16 at 01:16

score 1 · Accepted Answer · answered Nov 16 '16 at 01:16

You aren't doing anything with the result.

You can assign the result:

let anagrams = areTheStringsAnagrams(first: firstString, second: secondString)

If you don't need the result, you have two options. You can either assign to _

_ = areTheStringsAnagrams(first: firstString, second: secondString)

or you could mark the function with @discardableResult

@discardableResult
func areTheStringsAnagrams(first: String, second: String) -> Bool {
    return first.characters.sorted() == second.characters.sorted()
}

In this case, I wouldn't do the last option since if you ignore the result, what was the point of calling it?

Thanks for the answer. Awesome! – Eric Nov 16 '16 at 01:17 — Eric, Nov 16 '16 at 01:17

score 0 · Answer 2 · answered Nov 16 '16 at 01:15

0

The compiler is telling you that you are invoking a function that returns a value but you are not using that value. This could be an error on the developer side so the compiler shows a warning message.

answered Nov 16 '16 at 01:15

Luca Angeletti

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Return a boolean value from a function in Swift 3.0

2 Answers2