Converting Character and CodePoint in Swift

Question

Can I convert directly between a Swift Character and its Unicode numeric value? That is:

var i:Int = ...  // A plain integer index.
var myCodeUnit:UInt16 = myString.utf16[i]
// Would like to say myChar = myCodeUnit as Character, or equivalent.

or...

var j:String.Index = ... // NOT an integer!
var myChar:Character = myString[j]
// Would like to say myCodeUnit = myChar as UInt16

I can say:

myCodeUnit = String(myChar).utf16[0]

but this means creating a new String for each character. And I am doing this thousands of times (parsing text) so that is a lot of new Strings that are immediately being discarded.

Answer 1

The type Character represents a "Unicode grapheme cluster", which can be multiple Unicode codepoints. If you want one Unicode codepoint, you should use the type UnicodeScalar instead.

Answer 2

As per the swift book:

String to Code Unit

To get codeunit/ordinals for each character of the String, you can do the following:

var yourSwiftString = "甲乙丙丁"
for scalar in yourSwiftString.unicodeScalars {
    print("\(scalar.value) ")
}

Code Unit to String

Because swift current does not have a way to convert ordinals/code units back to UTF, the best way I found is to still NSString. i.e. if you have int ordinals (32bit but representing the 21bit codepoints) you can use the following to convert to Unicode:

var i = 22247
var unicode_str = NSString(bytes: &i, length: 4, encoding: NSUTF32LittleEndianStringEncoding)

Obviously if you want to convert a array of ints, you'll need to pack them into a array first.