Should I set my Strings to Nil or Empty? - swift

Question

I have a Meeting class where I parse the user's calendar to determine the properties of that class. Most of these fields are Strings that can potentially have nothing in them. When I discover these fields are empty is it better to set them to empty "" or make them optional and set them to nil?
/**
Parses calendar entry to create a Meeting object.
- parameter calendarEvent: The calendar entry we want to parse
- returns: A Meeting Object with the relevant information extracted from the calendar entry.
*/
public static func parse(calendarEvent: EKEvent) -> Meeting {
let location = calendarEvent.location ?? ""
let description = calendarEvent.notes ?? ""
let allInput = "\(calendarEvent.title)\n\(location)\n\(description)"
let parsedHostCodes = parseHostCode(from: allInput)
let parsedPasscodes = parseParticipantCode(from: allInput, hostCodes: parsedHostCodes)
let parsedPhoneNumbers = parsePhoneNumber(from: allInput, codes: parsedPasscodes + parsedHostCodes)
return Meeting(
UUID: calendarEvent.eventIdentifier,
title: calendarEvent.title,
description: description,
location: location,
startTime: calendarEvent.startDate,
endTime: calendarEvent.endDate,
allday: calendarEvent.isAllDay,
participantCodes: parsedPasscodes,
hostcodes: parsedHostCodes,
phoneNumbers: parsedPhoneNumbers,
host: retrieveHost(from: calendarEvent.organizer),
attendees: parseParticipants(from: calendarEvent.attendees),
provider: allInput.contains(pattern: attRegex) ? .att : .unknown)
}

Answer 1

Optionals are designed to determine the absence of data. If that's what your program checks for, then you really should use the feature. It's well worth it in the long run in situations where you can take advantage of "Optional Chaining" and "Auto-unwrap":
struct Event {
let location: String?
}
struct Day {
let events: [Event]?
}
var events: [Event]?
let currentDay: Day?
events = [Event(location: "conf room A1")]
currentDay = Day(events: events)
if let events = currentDay?.events {
for event in events {
if let location = event.location {
print(location)
}
}
}
There's a lot more going on here than what you see. First of all, I made everything Optional since it's likely the case in your code.
The first line of the "if let" is using "Optional Chaining". If either currentDay or currentDay.events is nil, the "if" block won't get executed. If currentDay and currentDay.events is not nil, currentDay.events will be auto-unwrapped and get assigned to "events" and then code execution will drop into the "if" block. Next, depending if there are any events for that day (i.e. array count), the "if let location = event.location" also checks if location is nil or not, and if it's not nil, will auto-unwrap and assign to "location" and will print the value.
If any of those Optionals are nil, then nothing in your code needs to change. Here I removed the assignment of "events" and "currentDay" so that they're both nil:
var events: [Event]?
let currentDay: Day? = nil
if let events = currentDay?.events {
for event in events {
if let location = event.location {
print(location)
}
}
}
As you can see, taking advantage of Optionals will result and less maintenance and generally cleaner code in the long run.

Answer 2

In general, if you need to check if a variable has a valid value at some point in your code, it is better to set up the variable as an Optional rather than set it up as an initial value. This is exactly what Optionals were designed for, so that you can check at any point in your code whether that specific variable has been set up or not without giving it any meaningful value.
For strings, "" could easily work as well, since in most cases an empty String literal("") is not a meaningful value, so you can easily check for it, but it is better practice to use Optionals, since they provide more sophisticated methods to check if they have been set or not then to check if a String equals "" or not.

Answer 3

This question must have been asked a lot of times.
Well, nil or "" is depend on your property data, nil used when an object or value is may exist or not. and also assigning nil is very handy when you check it's value using guard and if let. nil raised the question of possibility.
You can also use "". it's work also well, but sometimes it's become headache while comparing default empty value from response.