Swift 3的更新：

let formatter = DateFormatter()
formatter.dateFormat = "dd/MM/yyyy"
formatter.calendar = Calendar(identifier: .gregorian)
let date = Date()
let dateInGrogrian = formatter.string(from: date)

print(dateInGrogrian)

formatter.calendar = Calendar(identifier: .persian)
formatter.dateFormat = "dd/MM/yyyy"
print("Converted date to Hijri = \(formatter.string(from: date))")