This is a Swift implementation of Kamil Harasimowicz's any-base npm package.
let dec2hex = try! AnyBase(AnyBase.DEC, AnyBase.HEX)
let shortId = try! AnyBase(AnyBase.DEC, "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-+!@#$^")
let longId = try! AnyBase("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-+!@#$^", AnyBase.DEC)
print(try! dec2hex.convert("123456")) // return: '1e240'
print(try! shortId.convert("1234567890")) // return: 'PtmIa'
print(try! longId.convert("PtmIa")) // return: '1234567890'