Swiftier version of https://stackoverflow.com/a/42079976/3939277

SO-Answer-42079976.swift

import Foundation



public extension Array where Element == UInt8 {
    
    // MARK: - Constants
    
    /// This is used by the `toHexString()` method
    private static let uppercaseHexCharacters : [Character] =
        [ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F" ]
    
    
    
    // MARK: - Public methods
    
    /// Converts a byte array into a string containing uppercase hex characters, without any additional formatting.
    func toHexString() -> String {
        var stringToReturn = ""
        
        for byte in self {
            let intValue = Int(byte)
            stringToReturn.append(Self.uppercaseHexCharacters[intValue >> 4])
            stringToReturn.append(Self.uppercaseHexCharacters[intValue & 0x0f])
        }
        return stringToReturn
    }
}