CODEWITHSUNDEEP
swifttry-catch
Matthew Folbigg
Matthew Folbigg

Reputation: 192

Using variable/constant outside of do{}catch{} - swift2

So on a button press I'm creating splitLat: [Double] from a throwing function called splitLatitude that takes currentLocation: CLLocationCoordinate2D?. I then want to use splitLat as a Label (its going to be used for other things as well but this serves the example) 

@IBAction func ButtonPress() {
      let splitLat = try self.splitLatitude(self.currentLocation)
      LatSplitLabel.text = "\(splitLat)"
}

this gets a error "Errors thrown from here are not handled"

I resolve this by putting it in a do catch block 

    do{
        let splitLat = try self.splitLatitude(self.currentLocation)
    } catch {
        print("error") //Example - Fix
    }

but the when i try to set the label later on splitLat is an "unresolved identifier"

New to swift and programming in general, am i missing something basic/ do i have a mis understanding? is there a way i can use the constant from the do {} statement outside of the do statement. Tried return but that is reserved for functions.

Really appreciate any help

Thanks

Upvotes: 6

Views: 3601

Answers (3)

Rich Waters
Rich Waters

Reputation: 1587

A 3rd option is to use a closure:

 let splitLat:String = { 
     do {
         return try self.splitLatitude(self.currentLocation)
     }
     catch {
         print("error") //Example - Fix
         return ""
     }
 }()
 LatSplitLabel.text = "\(splitLat)"

Upvotes: 3

Christopher Harris
Christopher Harris

Reputation: 682

This is a scoping error if you want to succeed execution after the do/catch block. You must declare the variable outside of this do/catch scope in order to utilize it after the do/catch execution.

Try this:

var splitLat: <initialType> = <initialValue>
do {
    let splitLat = try self.splitLatitude(self.currentLocation)
} catch {
    print("error")
}

print(splitLat)

Here is a concocted example that runs in a Swift 2.2 playground:

enum Errors: ErrorType {
    case SomeBadError
}

func getResult(param: String) throws -> Bool {
    if param == "" {
        throw Errors.SomeBadError
    }
    return true
}

var result = false
do {
   result = try getResult("it")
} catch {
   print("Some error")
}

print(result)

Upvotes: 1

Daniel Krom
Daniel Krom

Reputation: 10058

You have two options (I'll assume that splitLat is String type)

do{
    let splitLat = try self.splitLatitude(self.currentLocation)
    //do rest of the code here
} catch {
    print("error") //Example - Fix
}

second option, predeclare the variable

let splitLat : String? //you can late init let vars from swift 1.2
do{
    splitLat = try self.splitLatitude(self.currentLocation)
} catch {
    print("error") //Example - Fix
}
//Here splitLat is recognized

Now, some explanation of your problem. in Swift (and many other languages) variables are only defined inside the scope they are defined

scope is defined between these brackets {/* scope code */ }

{
    var x : Int

    {
        //Here x is defined, it is inside the parent scope
        var y : Int
    }
    //Here Y is not defined, it is outside it's scope
}
//here X is outside the scope, undefined

Upvotes: 10

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