CODEWITHSUNDEEP
arraysswiftloopsswitch-statement
Vadim Nikolaev
Vadim Nikolaev

Reputation: 2132

Error in switch convert in swift

I have array of arrays - var days: [[Int]] = [[1], [1,2,3], [7]] and I'd like to convert Int into name by String and add it at new array arrayOfStringDays. My code:

var days: [[Int]] = [[1], [1,2,3], [7]]    
var arrayOfStringDays = [[String]]() 

            for i in 0..<days.count {

                switch days[i] {
                    case [1]:
                        arrayOfStringDays.append(["one"])
                    case [1,2,3]:
                        arrayOfStringDays.append(["one, two, three"])
                    case [7]:
                        arrayOfStringDays.append(["seven"])
                    default:
                        break
                } 
            }

but I see error near every case:

Expression pattern of type '[Int]' cannot match values of type '[Int]'

in what is my mistake? thanks!

Upvotes: 1

Views: 158

Answers (2)

Martin R
Martin R

Reputation: 539705

Update: Conditional conformance has been implemented Swift 4.1, and in particular arrays (and some other collection types) conform to Equatable if their elements do.

Your code now compiles without problems in Xcode 9.3.

The switch statement uses the "pattern-match" operator

public func ~=<T : Equatable>(a: T, b: T) -> Bool

to compare the given value against the various cases. The problem is that Array does not conform to Equatable, even if the array elements are Equatable. (This is going to change with Swift 4, see SE-0143 Conditional conformances.)

May I suggest a different solution? A nested map to convert the nested array, and a number formatter with "spell-out" style to convert numbers to words:

let days: [[Int]] = [[1], [1,2,3], [7]]

let formatter = NumberFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.numberStyle = .spellOut

let arrayOfStringDays = days.map {
    $0.map { formatter.string(from: $0 as NSNumber) ?? String($0) }
}

print(arrayOfStringDays)
// [["one"], ["one", "two", "three"], ["seven"]]

You can also set the formatter locale to a different language, or use the default value to get the result in the user's default language. Example:

formatter.locale = Locale(identifier: "ru")
// ...
print(arrayOfStringDays)
// [["один"], ["один", "два", "три"], ["семь"]]

Upvotes: 4

ERbittuu
ERbittuu

Reputation: 978

I don't know about exact error, but you can do conversion of [[Int]] something like this.

var days: [[Int]] = [[1], [1,2,3], [7]]

let numberStr = ["Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"]

let daysInString = days.map { (intList) -> [String] in
    return intList.map({ (intValue) -> String in
        return numberStr[intValue]
    })
}
print(daysInString)

// Output : [["One"], ["One", "Two", "Three"], ["Seven"]]

Upvotes: 1

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