Uppercase the first character of a Swift string

StringExtensions.swift

import Foundation

extension String {    
  
    func firstCharacterUpperCase() -> String {
        if let firstCharacter = characters.first, characters.count > 0 {
            return replacingCharacters(in: startIndex ..< index(after: startIndex), with: String(firstCharacter).uppercased())
        }
        return self
    }
}

// use
let myString = "hello world!"

print(myString.firstCharacterUpperCase()) // Hello world!