BLEMingleiOS-master/BLEMingleiOS/BLEMingle.swift:259:106:
Expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions
the line is
let finalString = rev[0..<7] + "-" + rev[8..<11] + "-" + rev[12..<15] + "-" + rev[16..<19] + "-" + rev[20..<31]