Convert Array of UnicodeScalar into String in Swift

Question

I have an array of unicode scalars (Type is [UnicodeScalar])

like:

let array = [UnicodeScalar("f")!, UnicodeScalar("o")!, UnicodeScalar("o")!]

or

let array2 = "bar".unicodeScalars

how can I convert efficiently these arrays into a strings again?

Expect:

let string1 = ?? // "foo"
let string2 = ?? // "bar"

Answer 1

The second case is simpler because array2 is a UnicodeScalarView and not an array:

let array2 = "bar".unicodeScalars

let str2 = String(array2)
print(str2) // bar

If you have an array (or any sequence) of Unicode scalars then you can start with an empty string and append the elements to its unicodeScalars view:

let array = [UnicodeScalar("f")!, UnicodeScalar("o")!, UnicodeScalar("o")!]
// Or: let array: [UnicodeScalar] = ["f", "o", "o"]

var str1 = ""
str1.unicodeScalars.append(contentsOf: array)
print(str1) // foo

Of course you can define a custom extension for that purpose:

extension String {
    init<S: Sequence>(unicodeScalars ucs: S)
        where S.Iterator.Element == UnicodeScalar
    {
        var s = ""
        s.unicodeScalars.append(contentsOf: ucs)
        self = s
    }
}

let str1 = String(unicodeScalars: array)

Answer 2

You can use this extension from @dfri to initialize a string from a UnicodeScalar sequence as follow:

extension Sequence where Element == UnicodeScalar { 
    var string: String { .init(String.UnicodeScalarView(self)) } 
}

---

let array: [UnicodeScalar] = ["f", "o", "o"]
print(array.string) //  "foo\n"

Answer 3

Another way to convert [UnicodeScalar] to String:

let array = [UnicodeScalar("f")!, UnicodeScalar("o")!, UnicodeScalar("o")!]
let string1 = String(array.map{Character($0)})
print(string1 == "foo") //->true

Answer 4

With Swift 5, you can use one of the following ways in order to get a string from a collection of Unicode scalars.

---

#1. Using String's init(_:) initializer

String has an init(_:) initializer with the following declaration:

init(_ unicodeScalars: String.UnicodeScalarView)

Creates a string corresponding to the given collection of Unicode scalars.

The Playground sample code below shows how to use init(_:) in order to get a String instance from a String.UnicodeScalarView instance:

let string = "foo"
let unicodeScalarView = string.unicodeScalars

let newString = String(unicodeScalarView)
print(newString) // prints: foo

If you initially have an array of Unicode scalars, you can convert it first to a String.UnicodeScalarView instance using String.UnicodeScalarView's init(_:) initializer:

let scalarsArray = [Unicode.Scalar("f"), Unicode.Scalar("o"), Unicode.Scalar("o")]

let unicodeScalarView = String.UnicodeScalarView(scalarsArray)
let newString = String(unicodeScalarView)
print(newString) // prints: foo

---

#2. Using String's init(_:) initializer

String has an init(_:) initializer with the following declaration:

init(_ scalar: Unicode.Scalar)

The following Playground sample codes show how to iterate over an array of Unicode scalars using String's init(_:) in order to create a new string:

let scalarsArray = [Unicode.Scalar("f"), Unicode.Scalar("o"), Unicode.Scalar("o")]

let string = scalarsArray.reduce("", { partialResult, scalar in
    return partialResult + String(scalar)
})
print(string) // prints: foo

let scalarsArray = [Unicode.Scalar("f"), Unicode.Scalar("o"), Unicode.Scalar("o")]

let newString = scalarsArray.map(String.init).joined()
print(newString) // prints: foo

---

#3. Using String.UnicodeScalarView's append(contentsOf:) method

If you have an existing string and want to append the elements of a Unicode scalars array into it, you can use append(contentsOf:):

let scalarsArray = [Unicode.Scalar("f"), Unicode.Scalar("o"), Unicode.Scalar("o")]

var newString = ""
newString.unicodeScalars.append(contentsOf: scalarsArray)
print(newString) // prints: foo

---

#4. Using Character's init(_:) initializer

Another approach would consist of iterating over a collection of Unicode scalars, convert them into characters (using Character's init(_:) initializer) then create a new string from those characters:

let scalarsArray = [Unicode.Scalar("f"), Unicode.Scalar("o"), Unicode.Scalar("o")]

let charactersArray = scalarsArray.map(Character.init)
let newString = String(charactersArray)
print(newString) // prints: foo