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Mobile Programming Video What I’m Up To

How to add Auth0 authentication to a SwiftUI app

Joey deVilla in his home office, holding an “Einstein” rubber duck up to the camera.
C’mon, how many programming tutorial videos have a scene like this?

If you’re making an iOS app, the odds are pretty good that sooner or later, you’re going to have to integrate authentication — login and logout — into it. I show you how to do that with Auth0 in both a video

…as well as a matching two-part article series that walks you through the process:

Both the video and article present how the final app will look and work:

Tap to view at full size.

And then they’ll get you started with a starter project:

Joey deVilla appears in the corner of the screen showing the starter project of Auth0’s iOS/SwiftUI authentication video.
Tap to view at full size.

I’ll walk you through the processes of getting Auth0 set up to recognize your app and creating a user with which to log in:

Joey deVilla appears in the corner of the screen showing the Auth0 dashboard in Auth0’s iOS/SwiftUI authentication video.
Tap to view at full size.

And then, I’ll show you how to add login and logout to the project’s app:

Joey deVilla appears in the corner of the screen, while adding login and logout to the starter project of Auth0’s iOS/SwiftUI authentication video.
Tap to view at full size.

And along the way, I’ll provide a brief intro to ID tokens, JWTs, and JWT.io:

Joey deVilla appears in the corner of the screen showing the JWT.io site in  Auth0’s iOS/SwiftUI authentication video.
Tap to view at full size.

Of course the video ends with an accordion number!

Joey deVilla plays accordion at the end of an Auth0 tutorial video.
Again, I ask: how many programming tutorial videos have a scene like this?

Once again, the here’s the video, How to Integrate Auth0 in a SwiftUI App, and here are the articles:

Whether you prefer to learn by watching video, reading, or a little bit of both, I hope you find these useful!

Categories
Programming Reading Material

My tutorial on iOS authentication using SwiftUI and Auth0

Banner: Get Started with iOS Authentication using SwiftUI

Hey, iOS developers! My latest tutorial article on the Auth0 blog shows you how to easily add authentication (that is, login and logout) to SwiftUI apps and display information from their user profile.

The article demonstrates the most basic use of the Auth0.swift SDK, the Auth0 SDK for all Apple platforms — not just iOS, but macOS, iPadOS, watchOS, and tvOS. It’s Auth0’s third most-used SDKs, accounting for more than one in ten API requests to Auth0 systems!

It’s a two-part tutorial. Part 1 of the tutorial starts with File → New Project…, adds some basic interactivity, adds the Auth0.swift package, walks you through setup on the Auth0 side, and finally enables login and logout:

iOS Simulator screen shot: Screen with title “SwiftUI Login Demo” and “Log in” button.
The app’s “logged out” screen.
iOS Simulator screen shot: Auth0 Universal Login screen.
Auth0’s Universal Login.
iOS Simulator screen shot: Screen with title “Logged in” and “Log out” button.
The app’s “logged in” screen.

Part 2 of the tutorial takes your basic login/logout app and gives it the ability to read user information from the user profile and display it onscreen:

iOS Simulator screen shot: Screen with title “Logged in”, photo of user, user]s name and email address, and “Log out” button.
The revised “logged in” screen.
Categories
Programming

Xcode 13 beta is available now!

Tap to view at full size.

The first day of WWDC ’21 has come and gone, which means that the beta for the upcoming version of Xcode is available now!

If you’ve been itching to try out the new Xcode (and especially the new SwiftUI), you can get it at Apple’s Developer site’s Downloads page. It’s currently installing on my machine as I write this.

Let’s do this.

Just a quick warning if this is your first time working with Xcode: the installation process can take a while. On my Auth0-issued 2019 MacBook Pro (2.6 GHz 6-core i7, 16 GB RAM), it took about a half hour or so to unzip itself into a functioning application.

Categories
Programming

Once more, in Swift (or: A solution to day one of Advent of Code 2019)

As I wrote in the previous post, the Advent of Code is happening soon — it start on Tuesday, December 1st and runs all the way to December 25th. If you want to give your programming skills a good workout or test, you’ll want to try out Advent of Code’s challenges!

The previous post featured Python solutions to the day one challenges from the 2019 edition of Advent of Code. In this post, I’ll present solutions written in Swift.

Day one challenge, part one

Here’s the first part of day one’s challenge:

The Elves quickly load you into a spacecraft and prepare to launch.

At the first Go / No Go poll, every Elf is Go until the Fuel Counter-Upper. They haven’t determined the amount of fuel required yet.

Fuel required to launch a given module is based on its mass. Specifically, to find the fuel required for a module, take its mass, divide by three, round down, and subtract 2.

For example:

  • For a mass of 12, divide by 3 and round down to get 4, then subtract 2 to get 2.
  • For a mass of 14, dividing by 3 and rounding down still yields 4, so the fuel required is also 2.
  • For a mass of 1969, the fuel required is 654.
  • For a mass of 100756, the fuel required is 33583.

The Fuel Counter-Upper needs to know the total fuel requirement. To find it, individually calculate the fuel needed for the mass of each module (your puzzle input), then add together all the fuel values.

What is the sum of the fuel requirements for all of the modules on your spacecraft?

While the problems in the Advent of Code are the same for every participant, the data for each participant is different (there’s a sign-up process, which gives you an account, your own progress tracker, and your own data). This prevents participants from simply sharing the solution.

Here are the module masses that were provided for my account:

134492
88713
84405
148193
95951
63545
137840
65558
124836
95431
77622
91864
108677
116871
119496
97172
86115
105704
68613
77114
114013
52766
57048
80814
73888
58253
135934
97409
112439
98262
116047
57456
124261
83006
101495
133449
111372
56146
87818
92209
149259
124559
141838
147988
65703
125566
59650
139564
92430
126307
120406
147383
84362
51529
146366
131840
53270
71886
118767
104311
126181
76964
129430
95489
91098
54133
110057
107276
118226
96104
135382
85152
61697
143417
148879
126846
130205
111170
86687
113729
123330
56976
148470
66028
129715
75686
74964
148258
72669
88809
78173
92699
124806
67217
139066
136002
135730
145708
142054
135772

I used the Python REPL for my Python-based solution. For my Swift-based solution, I used the closest analogue: an Xcode Playground.

Swift, like Python uses the three quotes to denote multiline strings. I used them to define a multiline string constant, rawInput, into which I pasted the data:

let rawInput = """
134492
88713
84405
148193
95951
63545
137840
65558
124836
95431
77622
91864
108677
116871
119496
97172
86115
105704
68613
77114
114013
52766
57048
80814
73888
58253
135934
97409
112439
98262
116047
57456
124261
83006
101495
133449
111372
56146
87818
92209
149259
124559
141838
147988
65703
125566
59650
139564
92430
126307
120406
147383
84362
51529
146366
131840
53270
71886
118767
104311
126181
76964
129430
95489
91098
54133
110057
107276
118226
96104
135382
85152
61697
143417
148879
126846
130205
111170
86687
113729
123330
56976
148470
66028
129715
75686
74964
148258
72669
88809
78173
92699
124806
67217
139066
136002
135730
145708
142054
135772
"""

With rawInput defined, it’s time to convert it from a multiline string into an array of strings, with each line getting turned into its own array element. The String class’ split method does this quite easily, and the result was the splitInput string array:

let splitInput = rawInput.split(separator: "\n")

The next step was to convert splitInput’s numbers-in-string-form into actual numbers. This process would involve applying the same function — the Int struct’s “init from string” method — to all the elements in an array, which is exactly what the map method is for:

let masses = splitInput.map {Int($0)!}

Swift’s map method takes a closure containing a function as its argument and applies that function to every item in the given array, creating a new array as its result.

In this case, the function in question is:

Int($0)!

Parameters passed into the closure begin with the $ character, which is then followed by a number specifying which parameter it is. The first parameter is $0, followed by the second parameter, $1, followed by the third parameter, $2, and so on.

Only one parameter is passed to the closure: $0, which represents the current element of the splitInput array. It’s fed into the init method of Int that takes a string and attempt to produce an integer. Since it’s possible that this method will be given a string that can’t be converted into an integer, the method’s return type is the optional type Int?.

Since I’m quite certain that all the strings in the splitInput array convert to integers, I used the ! operator to force unwrap the resulting Int? values.

The end result is masses, an array of integers. Each element in the array represents the mass of a component in the ship, and we need to calculate the fuel necessary to propel each component to the final destination.

This calculation involves applying a function to every element in masses, and that function is:

  • Divide the mass by 3, rounding down.
  • Subtracting 2 from the result above.

Once again, I used map:

let fuelRequirements = masses.map { mass in
    mass / 3 - 2
}

In the function above, mass and 3 are both integers, so mass / 3 is an integer division, which automatically rounds down.

The result of this mapping is fuelRequirements, an array of integers containing the fuel requirements for each module.

The result is the sum of all the values in fuelRequirements. Unfortunately, Swift doesn’t have a built in method for getting the sum of an array, so we’ll need to roll our own:

let totalFuel = fuelRequirements.reduce(0, +)

For my data, the result was 3454942. This turned out to be correct, so it was time to tackle part two.

Day one challenge, part two

Part two involved recalculating the fuel requirements when also taking into account the mass of the added fuel:

During the second Go / No Go poll, the Elf in charge of the Rocket Equation Double-Checker stops the launch sequence. Apparently, you forgot to include additional fuel for the fuel you just added.

Fuel itself requires fuel just like a module – take its mass, divide by three, round down, and subtract 2. However, that fuel also requires fuel, and that fuel requires fuel, and so on. Any mass that would require negative fuel should instead be treated as if it requires zero fuel; the remaining mass, if any, is instead handled by wishing really hard, which has no mass and is outside the scope of this calculation.

So, for each module mass, calculate its fuel and add it to the total. Then, treat the fuel amount you just calculated as the input mass and repeat the process, continuing until a fuel requirement is zero or negative. For example:

  • A module of mass 14 requires 2 fuel. This fuel requires no further fuel (2 divided by 3 and rounded down is 0, which would call for a negative fuel), so the total fuel required is still just 2.
  • At first, a module of mass 1969 requires 654 fuel. Then, this fuel requires 216 more fuel (654 / 3 - 2). 216 then requires 70 more fuel, which requires 21 fuel, which requires 5 fuel, which requires no further fuel. So, the total fuel required for a module of mass 1969 is 654 + 216 + 70 + 21 + 5 = 966.
  • The fuel required by a module of mass 100756 and its fuel is: 33583 + 11192 + 3728 + 1240 + 411 + 135 + 43 + 12 + 2 = 50346.

What is the sum of the fuel requirements for all of the modules on your spacecraft when also taking into account the mass of the added fuel? (Calculate the fuel requirements for each module separately, then add them all up at the end.)

This called for a recursive function, the Swift code for which is below:

func fuelRequired(mass: Int) -> Int {
    let result = mass / 3 - 2
    
    if result <= 0 {
        return 0
    } else {
        return result + fuelRequired(mass: result)
    }
}

I used this function to map the values in the masses array from part one onto a new array, updatedFuelRequirements

let updatedFuelRequirements = masses.map { fuelRequired(mass: $0) }

…and the sum of its the elements was the answer for part two:

let updatedTotalFuel = updatedFuelRequirements.reduce(0, +)

For my data, the answer was 5179544.

Categories
Programming

Converting a number from a numeric form into words in just four lines of Swift

Until I started working on a video tutorial for Apple’s Combine framework (coming soon to raywenderlich.com!), I had no idea that this existed.

Open a Swift playground in Xcode and enter the following code:

let formatter = NumberFormatter()
formatter.numberStyle = .spellOut
let number = 87654
let spelledOutNumber = formatter.string(for: NSNumber(integerLiteral: number))!
print("\(number) spelled out is \(spelledOutNumber).")

Run the playground code, and you’ll see this:

87654 spelled out is eighty-seven thousand six hundred fifty-four.

Having come from the world of C, where you format strings using printf() and formatting strings, and later from other languages where you use whatever formatting method its string class provides, I’ve ignored most of Swift’s classes that derive from Formatter — with one notable exception: DateFormatter, which is indispensable when working with dates and times.

I’m now looking for an excuse to use this capability.

As I typed “DateFormatter” a couple of paragraphs above, I remembered that DateFormatter had a locale property. It’s for ensuring that any dates you present are in the correct form for the locale:

I wondered:

  • Does NumberFormatter have a locale property?
  • What happens if I changed it to something other than my system’s default of US English?

So I changed the code in my playground to the following:

let formatter = NumberFormatter()
formatter.numberStyle = .spellOut
formatter.locale = Locale(identifier: "fil_PH")
let number = 87654
let spelledOutNumber = formatter.string(for: NSNumber(integerLiteral: number))!
print("\(number) spelled out in Filipino is \(spelledOutNumber).")

I ran the code and saw this…

87654 spelled out in Filipino is walóng pû’t pitóng libó’t anim na daán at limáng pû’t ápat.

…and my response was “Ay nako!” (translation: OMG!)

How about Korean?

let formatter = NumberFormatter()
formatter.numberStyle = .spellOut
formatter.locale = Locale(identifier: "ko_KR")
let number = 87654
let spelledOutNumber = formatter.string(for: NSNumber(integerLiteral: number))!
print("\(number) spelled out in Korean is \(spelledOutNumber).")

The output:

87654 spelled out in Korean is 팔만 칠천육백오십사.

My response: 세상에 (“Sesange!”, which is pretty much Korean for OMG!)

Try it out!  You might find this list of iOS locale string identifiers useful.

Categories
Programming

Dates and times in Swift 5, part 4: Adding Swift syntactic magic

Dates and times in Swift 5In this article, we’ll expand on material covered in the three previous articles in this series on working with dates and times in Swift 5:

A more readable way to work with Dates and DateComponents

Suppose we want to find out what the date and time will be 2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now will be.

If you recall what we covered in the last installment in this series, you’d probably use code like this:

var timeInterval = DateComponents(
  month: 2,
  day: 3,
  hour: 4,
  minute: 5,
  second: 6
)
let futureDate = Calendar.current.date(byAdding: timeInterval, to: Date())!
print("2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now is \(futureDate.description(with: Locale(identifier: "en_US"))).")

In the code above, we did the following:

  • We created an instance of a DateComponents struct.
  • We set its properties so that it would represent a time interval of 2 months, 3 days, 4 hours, 5 minutes, and 6 seconds.
  • We then used Calendar‘s date(byAdding:to:) method to add the time interval to a Date.

This code wouldn’t look out of place in a lot of other programming languages, but we can do better in Swift. What if I told you that by defining a few helper functions, you can turn the code above into the code below?

let coolerFutureDate = Date() + 2.months + 3.days + 4.hours + 5.minutes + 6.seconds
let coolerPastDate   = Date() - 2.months - 3.days - 4.hours - 5.minutes - 6.seconds

Or this code?

let coolerFutureDate = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
let coolerPastDate   = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago

I’d much rather write the code above. This article will cover the code necessary to make this kind of syntactic magic possible.

Overloading + and - so that we can add and subtract DateComponents

First, let’s write some code that allows us to add and subtract DateComponents. Start a new playground and enter the following code into it:

func +(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs)
}

func -(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs, multiplier: -1)
}

func combineComponents(_ lhs: DateComponents,
                       _ rhs: DateComponents,
                       multiplier: Int = 1)
  -> DateComponents {
    var result = DateComponents()
    result.nanosecond = (lhs.nanosecond ?? 0) + (rhs.nanosecond ?? 0) * multiplier
    result.second     = (lhs.second     ?? 0) + (rhs.second     ?? 0) * multiplier
    result.minute     = (lhs.minute     ?? 0) + (rhs.minute     ?? 0) * multiplier
    result.hour       = (lhs.hour       ?? 0) + (rhs.hour       ?? 0) * multiplier
    result.day        = (lhs.day        ?? 0) + (rhs.day        ?? 0) * multiplier
    result.weekOfYear = (lhs.weekOfYear ?? 0) + (rhs.weekOfYear ?? 0) * multiplier
    result.month      = (lhs.month      ?? 0) + (rhs.month      ?? 0) * multiplier
    result.year       = (lhs.year       ?? 0) + (rhs.year       ?? 0) * multiplier
    return result
}

In the code above, we’ve overloaded the + and - operators so that we can add and subtract DateComponents. I derived these functions from Axel Schlueter’s SwiftDateTimeExtensions library. He wrote them when Swift was still in beta; I updated them so that they compile with the current version and added a couple of tweaks of my own.

The addition and subtraction operations are so similar and so tedious, which is a sign that there’s an opportunity to DRY up the code. I factored out the duplicate code from both the + and - overloads and put it into its own method, combineComponents, which does the actual DateComponents addition and subtraction.

You may have noticed a lot of ?? operators in the code for combineComponents. ?? is referred to as the nil coalescing operator, and it’s a clever bit of syntactic shorthand. For the expression below:

let finalValue = someOptionalValue ?? fallbackValue

  • If someOptionalValue is not nil, finalValue is set to someOptionalValue‘s value.
  • If someOptionalValue is nil, finalValue is set to fallbackValue‘s value.

Let’s confirm that our new operator overloads work. Add the following to the playground and run it:

// Let's define a couple of durations of time
// ------------------------------------------

var oneDayFiveHoursTenMinutes = DateComponents(
  day: 1,
  hour: 5,
  minute: 10
)
var threeDaysTenHoursThirtyMinutes = DateComponents(
  day: 3,
  hour: 10,
  minute: 30
)


// Now let's add and subtract them
// -------------------------------

let additionResult = oneDayFiveHoursTenMinutes + threeDaysTenHoursThirtyMinutes
print("1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:")
print("\(additionResult.day!) days, \(additionResult.hour!) hours, and \(additionResult.minute!) minutes.")

let subtractionResult = threeDaysTenHoursThirtyMinutes - oneDayFiveHoursTenMinutes
print("1 day, 5 hours, and 10 minutes - 3 days, 10 hours, and 30 minutes equals:")
print("\(subtractionResult.day!) days, \(subtractionResult.hour!) hours, and \(subtractionResult.minute!) minutes.")

You should see the following output:

1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:
4 days, 15 hours, and 40 minutes.
1 day, 5 hours, and 10 minutes – 3 days, 10 hours, and 30 minutes equals:
2 days, 5 hours, and 20 minutes.

Overloading - so that we can negate DateComponents

Now that we can add and subtract DateComponents, let’s overload the unary minus so that we can negate DateComponents:

prefix func -(components: DateComponents) -> DateComponents {
  var result = DateComponents()
  if components.nanosecond != nil { result.nanosecond = -components.nanosecond! }
  if components.second     != nil { result.second     = -components.second! }
  if components.minute     != nil { result.minute     = -components.minute! }
  if components.hour       != nil { result.hour       = -components.hour! }
  if components.day        != nil { result.day        = -components.day! }
  if components.weekOfYear != nil { result.weekOfYear = -components.weekOfYear! }
  if components.month      != nil { result.month      = -components.month! }
  if components.year       != nil { result.year       = -components.year! }
  return result
}

With this overload defined, we can now use the unary minus to negate DateComponents. Add the following to the playground and run it:

let negativeTime = -oneDayFiveHoursTenMinutes
print("Negating 1 day, 5 hours, and 10 minutes turns it into:")
print("\(negativeTime.day!) days, \(negativeTime.hour!) hours, and \(negativeTime.minute!) minutes.")

You should see the following output:

Negating 1 day, 5 hours, and 10 minutes turns it into:
-1 days, -5 hours, and -10 minutes.

Overloading + and - so that we can add Dates and DateComponents and subtract DateComponents from Dates

With the unary minus defined, we can now define the following operations:

  • Date + DateComponents, which makes it easier to do date arithmetic.
  • DateComponents + Date, which should be possible because addition is commutative (which is just a fancy way of saying that a + b and b + a should give you the same result).
  • Date - DateComponents, which once again makes it easier to do date arithmetic.
// Date + DateComponents
func +(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return Calendar.current.date(byAdding: rhs, to: lhs)!
}

// DateComponents + Dates
func +(_ lhs: DateComponents, _ rhs: Date) -> Date
{
  return rhs + lhs
}

// Date - DateComponents
func -(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return lhs + (-rhs)
}

Note that we didn’t define an overload for calculating Date - DateComponents — such an operation doesn’t make any sense.

With these overloads defined, a lot of Date/DateComponents arithmetic in Swift becomes much easier to enter and read. Add the following to the playground and run it:

// What time will it be 1 day, 5 hours, and 10 minutes from now?
// -------------------------------------------------------------

// Here's the standard way of finding out:
let futureDate0 = Calendar.current.date(
  byAdding: oneDayFiveHoursTenMinutes,
  to: Date()
)

// With our overloads and function definitions, we can now do it this way:
let futureDate1 = Date() + oneDayFiveHoursTenMinutes
print("Date() + oneDayFiveHoursTenMinutes = \(futureDate1.description(with: Locale(identifier: "en_US")))")

// This will work as well:
let futureDate2 = oneDayFiveHoursTenMinutes + Date()
print("oneDayFiveHoursTenMinutes + Date() = \(futureDate2.description(with: Locale(identifier: "en_US")))")


// What time was it 3 days, 10 hours, and 30 minutes ago?
// ------------------------------------------------------

// Doing it the standard way takes some work
var minus3Days5Hours30minutes = threeDaysTenHoursThirtyMinutes
minus3Days5Hours30minutes.day = -threeDaysTenHoursThirtyMinutes.day!
minus3Days5Hours30minutes.hour = -threeDaysTenHoursThirtyMinutes.hour!
minus3Days5Hours30minutes.minute = -threeDaysTenHoursThirtyMinutes.minute!
let pastDate0 = Calendar.current.date(byAdding: minus3Days5Hours30minutes, to: Date())

// With our overloads and function definitions, it's so much easier:
let pastDate1 = Date() - threeDaysTenHoursThirtyMinutes
print("Date() - threeDaysTenHoursThirtyMinutes = \(pastDate1.description(with: Locale(identifier: "en_US")))")

On my computer, the output looked like this:

Date() + oneDayFiveHoursTenMinutes = Friday, May 29, 2020 at 3:20:54 PM Eastern Daylight Time
oneDayFiveHoursTenMinutes + Date() = Friday, May 29, 2020 at 3:20:54 PM Eastern Daylight Time
Date() – threeDaysTenHoursThirtyMinutes = Sunday, May 24, 2020 at 11:40:54 PM Eastern Daylight Time

Extending Date so that creating dates and debugging are simpler

Creating Dates in Swift is a roundabout process. Usually, you end up creating them in one of two ways:

  • Instantiating a DateComponents struct and then using it to create a Date using Calendar‘s date(from:) method, or
  • Creating a String representation of the Date and then using it to create a Date using DateFormatter‘s date(from:) method.

Let’s simplify things by extending the Date struct with a couple of convenient init method overloads. Let’s also make it easier to print out the value of a Date for debugging.

Add the following to the playground:

extension Date {

  init(year: Int,
       month: Int,
       day: Int,
       hour: Int = 0,
       minute: Int = 0,
       second: Int = 0,
       timeZone: TimeZone = TimeZone(abbreviation: "UTC")!) {
    var components = DateComponents()
    components.year = year
    components.month = month
    components.day = day
    components.hour = hour
    components.minute = minute
    components.second = second
    components.timeZone = timeZone
    self = Calendar.current.date(from: components)!
  }

  init(dateString: String) {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss zz"
    self = formatter.date(from: dateString)!
  }

  var desc: String {
    get {
      let PREFERRED_LOCALE = "en_US" // Use whatever locale you prefer!
      return self.description(with: Locale(identifier: PREFERRED_LOCALE))
    }
  }

}

With these methods, initializing Dates is a lot more simple. Add the following to the playground and run it:

// The Stevenote where the original iPhone was announced took place
// on January 9, 2007 at 10:00 a.m. PST
let iPhoneStevenoteDate = Date(year: 2007,
                               month: 1,
                               day: 9,
                               hour: 10,
                               minute: 0,
                               second: 0,
                               timeZone: TimeZone(abbreviation: "PST")!)
print("iPhoneStevenoteDate: \(iPhoneStevenoteDate.desc)")

// The original iPhone went on sale on June 27, 2007
let iPhoneReleaseDate = Date(year: 2007, month: 6, day: 27) // June 27, 2007, 00:00:00 UTC
print("iPhoneReleaseDate: \(iPhoneReleaseDate.desc)")

// The Stevenote where the original iPad was announced took place
// on January 27, 2010 at 10:00 a.m. PST
let iPadStevenoteDate = Date(dateString: "2010-01-27 10:00:00 PST")
print("iPadStevenoteDate: \(iPadStevenoteDate.desc)")

On my computer, the output looked like this:

iPhoneStevenoteDate: Tuesday, January 9, 2007 at 1:00:00 PM Eastern Standard Time
iPhoneReleaseDate: Tuesday, June 26, 2007 at 8:00:00 PM Eastern Daylight Time
iPadStevenoteDate: Wednesday, January 27, 2010 at 1:00:00 PM Eastern Standard Time

Overloading - so that we can use it to find the difference between two Dates

When we’re trying to determine the time between two given Dates, what we’re doing is finding the difference between them. Wouldn’t it be nice if we could use the - operator to find the difference between Dates, just as we can use it to find the difference between numbers?

Let’s code an overload to do just that. Add the following to the playground:

func -(_ lhs: Date, _ rhs: Date) -> DateComponents
{
  return Calendar.current.dateComponents(
    [.year, .month, .weekOfYear, .day, .hour, .minute, .second, .nanosecond],
    from: rhs,
    to: lhs)
}

Let’s test it in action. Add the following to the playground and run it:

let timeFromAnnouncementToRelease = iPhoneReleaseDate - iPhoneStevenoteDate
timeFromAnnouncementToRelease.year    // 0
timeFromAnnouncementToRelease.month   // 5
timeFromAnnouncementToRelease.day     // 17
timeFromAnnouncementToRelease.hour    // 7
timeFromAnnouncementToRelease.minute  // 0

// How long ago was the first moon landing, which took place
// on July 20, 1969, 20:18 UTC?
Date() - Date(dateString: "1969-07-20 20:18:00 UTC")
// At the time of writing, this value was a Date with the following properties:
// - year: 47 
// - month: 1 
// - day: 9 
// - hour: 22 
// - minute: 14

On my computer, the output looked like this:

The first iPhone users had to wait this long:
0 years, 5 months, 2 weeks, 3 days, 7 hours, and 0 minutes.
It’s been this long since the first moon landing:
50 years, 10 months, 1 weeks, 0 days, 18 hours, and 22 minutes.

Extending Int to add some syntactic magic to date components

We’ve already got some syntactic niceties, but the real Swift magic happens when we add this code to the mix. Add the following to the playground:

extension Int {

  var second: DateComponents {
    var components = DateComponents()
    components.second = self;
    return components
  }
  
  var seconds: DateComponents {
    return self.second
  }
  
  var minute: DateComponents {
    var components = DateComponents()
    components.minute = self;
    return components
  }
  
  var minutes: DateComponents {
    return self.minute
  }
  
  var hour: DateComponents {
    var components = DateComponents()
    components.hour = self;
    return components
  }
  
  var hours: DateComponents {
    return self.hour
  }
  
  var day: DateComponents {
    var components = DateComponents()
    components.day = self;
    return components
  }
  
  var days: DateComponents {
    return self.day
  }
  
  var week: DateComponents {
    var components = DateComponents()
    components.weekOfYear = self;
    return components
  }
  
  var weeks: DateComponents {
    return self.week
  }
  
  var month: DateComponents {
    var components = DateComponents()
    components.month = self;
    return components
  }
  
  var months: DateComponents {
    return self.month
  }
  
  var year: DateComponents {
    var components = DateComponents()
    components.year = self;
    return components
  }
  
  var years: DateComponents {
    return self.year
  }
  
}

This additions to Int allow us to convert Ints to DateComponents in an easy-to-read way, and with our overloads to add and subtract DateComponents to and from each other, and to add Dates to DateComponents, we can now perform all sorts of syntactic magic like this (add the following to the playground and run it):

// A quick test of some future dates
print("One hour from now is: \((Date() + 1.hour).desc)")
print("One day from now is: \((Date() + 1.day).desc)")
print("One week from now is: \((Date() + 1.week).desc)")
print("One month from now is: \((Date() + 1.month).desc)")
print("One year from now is: \((Date() + 1.year).desc)")

// What was the date 10 years, 9 months, 8 days, 7 hours, and 6 minutes ago?
let aLittleWhileBack = Date() - 10.years - 9.months - 8.days - 7.hours - 6.minutes
print("10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: \(aLittleWhileBack.desc)")

On my computer, the output looked like this:

One hour from now is: Thursday, May 28, 2020 at 11:57:49 AM Eastern Daylight Time
One day from now is: Friday, May 29, 2020 at 10:57:49 AM Eastern Daylight Time
One week from now is: Thursday, June 4, 2020 at 10:57:49 AM Eastern Daylight Time
One month from now is: Sunday, June 28, 2020 at 10:57:49 AM Eastern Daylight Time
One year from now is: Friday, May 28, 2021 at 10:57:49 AM Eastern Daylight Time
10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: Thursday, August 20, 2009 at 3:51:49 AM Eastern Daylight Time

Extending DateComponents to add even more syntactic magic: fromNow and ago

And finally, a couple of additions to the DateComponents struct to make Date/DateComponent calculations even more concise and readable. Add these to the playground:

extension DateComponents {
  
  var fromNow: Date {
    return Calendar.current.date(byAdding: self,
                                 to: Date())!
  }
  
  var ago: Date {
    return Calendar.current.date(byAdding: -self,
                                 to: Date())!
  }
  
}

Let’s try them out! Add these to the playground and run them:

// We’re now in Serious Syntax Magic Land!
// ---------------------------------------

print("2.weeks.fromNow: \(2.weeks.fromNow.desc)")
print("3.months.fromNow: \(3.months.fromNow.desc)")

let futureDate3 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
print("futureDate3: \(futureDate3.desc)")

let pastDate2 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago
print("pastDate2: \(pastDate2.desc)")

On my computer, the output looked like this:

2.weeks.fromNow: Thursday, June 11, 2020 at 11:03:36 AM Eastern Daylight Time
3.months.fromNow: Friday, August 28, 2020 at 11:03:36 AM Eastern Daylight Time
futureDate3: Friday, July 31, 2020 at 3:08:42 PM Eastern Daylight Time
pastDate2: Wednesday, March 25, 2020 at 6:58:30 AM Eastern Daylight Time

Wrapping it all up

Here’s the playground containing all the code we just worked with:

import UIKit

var timeInterval = DateComponents(
  month: 2,
  day: 3,
  hour: 4,
  minute: 5,
  second: 6
)
let futureDate = Calendar.current.date(byAdding: timeInterval, to: Date())!
print("2 months, 3 days, 4 hours, 5 minutes, and 6 seconds from now is \(futureDate.description(with: Locale(identifier: "en_US"))).")


// Overloading + and - so that we can add and subtract DateComponents
// ==================================================================

func +(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs)
}

func -(_ lhs: DateComponents, _ rhs: DateComponents) -> DateComponents {
  return combineComponents(lhs, rhs, multiplier: -1)
}

func combineComponents(_ lhs: DateComponents,
                       _ rhs: DateComponents,
                       multiplier: Int = 1)
  -> DateComponents {
    var result = DateComponents()
    result.nanosecond = (lhs.nanosecond ?? 0) + (rhs.nanosecond ?? 0) * multiplier
    result.second     = (lhs.second     ?? 0) + (rhs.second     ?? 0) * multiplier
    result.minute     = (lhs.minute     ?? 0) + (rhs.minute     ?? 0) * multiplier
    result.hour       = (lhs.hour       ?? 0) + (rhs.hour       ?? 0) * multiplier
    result.day        = (lhs.day        ?? 0) + (rhs.day        ?? 0) * multiplier
    result.weekOfYear = (lhs.weekOfYear ?? 0) + (rhs.weekOfYear ?? 0) * multiplier
    result.month      = (lhs.month      ?? 0) + (rhs.month      ?? 0) * multiplier
    result.year       = (lhs.year       ?? 0) + (rhs.year       ?? 0) * multiplier
    return result
}


// Let's define a couple of durations of time
// ------------------------------------------

var oneDayFiveHoursTenMinutes = DateComponents(
  day: 1,
  hour: 5,
  minute: 10
)
var threeDaysTenHoursThirtyMinutes = DateComponents(
  day: 3,
  hour: 10,
  minute: 30
)


// Now let's add and subtract them
// -------------------------------

let additionResult = oneDayFiveHoursTenMinutes + threeDaysTenHoursThirtyMinutes
print("1 day, 5 hours, and 10 minutes + 3 days, 10 hours, and 30 minutes equals:")
print("\(additionResult.day!) days, \(additionResult.hour!) hours, and \(additionResult.minute!) minutes.")

let subtractionResult = threeDaysTenHoursThirtyMinutes - oneDayFiveHoursTenMinutes
print("1 day, 5 hours, and 10 minutes - 3 days, 10 hours, and 30 minutes equals:")
print("\(subtractionResult.day!) days, \(subtractionResult.hour!) hours, and \(subtractionResult.minute!) minutes.")


// Overloading - so that we can negate DateComponents
// --------------------------------------------------

// We'll need to overload unary - so we can negate components
prefix func -(components: DateComponents) -> DateComponents {
  var result = DateComponents()
  if components.nanosecond != nil { result.nanosecond = -components.nanosecond! }
  if components.second     != nil { result.second     = -components.second! }
  if components.minute     != nil { result.minute     = -components.minute! }
  if components.hour       != nil { result.hour       = -components.hour! }
  if components.day        != nil { result.day        = -components.day! }
  if components.weekOfYear != nil { result.weekOfYear = -components.weekOfYear! }
  if components.month      != nil { result.month      = -components.month! }
  if components.year       != nil { result.year       = -components.year! }
  return result
}


let negativeTime = -oneDayFiveHoursTenMinutes
print("Negating 1 day, 5 hours, and 10 minutes turns it into:")
print("\(negativeTime.day!) days, \(negativeTime.hour!) hours, and \(negativeTime.minute!) minutes.")


// Overloading + and - so that we can add Dates and DateComponents
// and subtract DateComponents from Dates

// Date + DateComponents
func +(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return Calendar.current.date(byAdding: rhs, to: lhs)!
}

// DateComponents + Dates
func +(_ lhs: DateComponents, _ rhs: Date) -> Date
{
  return rhs + lhs
}

// Date - DateComponents
func -(_ lhs: Date, _ rhs: DateComponents) -> Date
{
  return lhs + (-rhs)
}


// What time will it be 1 day, 5 hours, and 10 minutes from now?
// -------------------------------------------------------------

// Here's the standard way of finding out:
let futureDate0 = Calendar.current.date(
  byAdding: oneDayFiveHoursTenMinutes,
  to: Date()
)

// With our overloads and function definitions, we can now do it this way:
let futureDate1 = Date() + oneDayFiveHoursTenMinutes
print("Date() + oneDayFiveHoursTenMinutes = \(futureDate1.description(with: Locale(identifier: "en_US")))")

// This will work as well:
let futureDate2 = oneDayFiveHoursTenMinutes + Date()
print("oneDayFiveHoursTenMinutes + Date() = \(futureDate2.description(with: Locale(identifier: "en_US")))")


// What time was it 3 days, 10 hours, and 30 minutes ago?
// ------------------------------------------------------

// Doing it the standard way takes some work
var minus3Days5Hours30minutes = threeDaysTenHoursThirtyMinutes
minus3Days5Hours30minutes.day = -threeDaysTenHoursThirtyMinutes.day!
minus3Days5Hours30minutes.hour = -threeDaysTenHoursThirtyMinutes.hour!
minus3Days5Hours30minutes.minute = -threeDaysTenHoursThirtyMinutes.minute!
let pastDate0 = Calendar.current.date(byAdding: minus3Days5Hours30minutes, to: Date())

// With our overloads and function definitions, it's so much easier:
let pastDate1 = Date() - threeDaysTenHoursThirtyMinutes
print("Date() - threeDaysTenHoursThirtyMinutes = \(pastDate1.description(with: Locale(identifier: "en_US")))")


// Extending Date so that creating dates and debugging are simpler
// ===============================================================

extension Date {

  init(year: Int,
       month: Int,
       day: Int,
       hour: Int = 0,
       minute: Int = 0,
       second: Int = 0,
       timeZone: TimeZone = TimeZone(abbreviation: "UTC")!) {
    var components = DateComponents()
    components.year = year
    components.month = month
    components.day = day
    components.hour = hour
    components.minute = minute
    components.second = second
    components.timeZone = timeZone
    self = Calendar.current.date(from: components)!
  }

  init(dateString: String) {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss zz"
    self = formatter.date(from: dateString)!
  }

  var desc: String {
    get {
      let PREFERRED_LOCALE = "en_US" // Use whatever locale you prefer!
      return self.description(with: Locale(identifier: PREFERRED_LOCALE))
    }
  }

}


// The Stevenote where the original iPhone was announced took place
// on January 9, 2007 at 10:00 a.m. PST
let iPhoneStevenoteDate = Date(year: 2007,
                               month: 1,
                               day: 9,
                               hour: 10,
                               minute: 0,
                               second: 0,
                               timeZone: TimeZone(abbreviation: "PST")!)
print("iPhoneStevenoteDate: \(iPhoneStevenoteDate.desc)")

// The original iPhone went on sale on June 27, 2007
let iPhoneReleaseDate = Date(year: 2007, month: 6, day: 27) // June 27, 2007, 00:00:00 UTC
print("iPhoneReleaseDate: \(iPhoneReleaseDate.desc)")

// The Stevenote where the original iPad was announced took place
// on January 27, 2010 at 10:00 a.m. PST
let iPadStevenoteDate = Date(dateString: "2010-01-27 10:00:00 PST")
print("iPadStevenoteDate: \(iPadStevenoteDate.desc)")


// Overloading - so that we can use it to find the difference
// between two Dates
// ==========================================================

func -(_ lhs: Date, _ rhs: Date) -> DateComponents
{
  return Calendar.current.dateComponents(
    [.year, .month, .weekOfYear, .day, .hour, .minute, .second, .nanosecond],
    from: rhs,
    to: lhs)
}

// How long was it between the announcement of the original iPhone
// and its release in the stores?
let iPhoneWait = iPhoneReleaseDate - iPhoneStevenoteDate
print("The first iPhone users had to wait this long: ")
print("\(iPhoneWait.year!) years, " +
  "\(iPhoneWait.month!) months, " +
  "\(iPhoneWait.weekOfYear!) weeks, " +
  "\(iPhoneWait.day!) days, " +
  "\(iPhoneWait.hour!) hours, and " +
  "\(iPhoneWait.minute!) minutes.")

// How long ago was the first moon landing, which took place
// on July 20, 1969, 20:18 UTC?
let timeSinceMoonLanding = Date() - Date(dateString: "1969-07-20 20:18:00 UTC")
print("It’s been this long since the first moon landing: ")
print("\(timeSinceMoonLanding.year!) years, " +
  "\(timeSinceMoonLanding.month!) months, " +
  "\(timeSinceMoonLanding.weekOfYear!) weeks, " +
  "\(timeSinceMoonLanding.day!) days, " +
  "\(timeSinceMoonLanding.hour!) hours, and " +
  "\(timeSinceMoonLanding.minute!) minutes.")


// Extending Int to add some syntactic magic to date components
// ============================================================

extension Int {

  var second: DateComponents {
    var components = DateComponents()
    components.second = self;
    return components
  }

  var seconds: DateComponents {
    return self.second
  }

  var minute: DateComponents {
    var components = DateComponents()
    components.minute = self;
    return components
  }

  var minutes: DateComponents {
    return self.minute
  }

  var hour: DateComponents {
    var components = DateComponents()
    components.hour = self;
    return components
  }

  var hours: DateComponents {
    return self.hour
  }

  var day: DateComponents {
    var components = DateComponents()
    components.day = self;
    return components
  }

  var days: DateComponents {
    return self.day
  }

  var week: DateComponents {
    var components = DateComponents()
    components.weekOfYear = self;
    return components
  }

  var weeks: DateComponents {
    return self.week
  }

  var month: DateComponents {
    var components = DateComponents()
    components.month = self;
    return components
  }

  var months: DateComponents {
    return self.month
  }

  var year: DateComponents {
    var components = DateComponents()
    components.year = self;
    return components
  }

  var years: DateComponents {
    return self.year
  }

}


// A quick test of some future dates
print("One hour from now is: \((Date() + 1.hour).desc)")
print("One day from now is: \((Date() + 1.day).desc)")
print("One week from now is: \((Date() + 1.week).desc)")
print("One month from now is: \((Date() + 1.month).desc)")
print("One year from now is: \((Date() + 1.year).desc)")

// What was the date 10 years, 9 months, 8 days, 7 hours, and 6 minutes ago?
let aLittleWhileBack = Date() - 10.years - 9.months - 8.days - 7.hours - 6.minutes
print("10 years, 9 months, 8 days, 7 hours, and 6 minutes ago, it was: \(aLittleWhileBack.desc)")


// Extending DateComponents to add even more syntactic magic: fromNow and ago
// ==========================================================================

extension DateComponents {

  var fromNow: Date {
    return Calendar.current.date(byAdding: self,
                                 to: Date())!
  }

  var ago: Date {
    return Calendar.current.date(byAdding: -self,
                                 to: Date())!
  }

}

// We’re now in Serious Syntax Magic Land!
// ---------------------------------------

print("2.weeks.fromNow: \(2.weeks.fromNow.desc)")
print("3.months.fromNow: \(3.months.fromNow.desc)")

let futureDate3 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).fromNow
print("futureDate3: \(futureDate3.desc)")

let pastDate2 = (2.months + 3.days + 4.hours + 5.minutes + 6.seconds).ago
print("pastDate2: \(pastDate2.desc)")

You can download the playground here (4KB, zipped Xcode playground file).

The How to work with dates and times in Swift 5 series

Here are the articles in this series:

Categories
Programming

Dates and times in Swift 5, part 3: Date arithmetic

abacus with toy clock
You can actually buy this thing on Etsy! Tap the photo for details.

What we’ve covered so far, and what we’ll cover in this installment

Dates and times in Swift 5So far, in this series on programming with dates and times in Swift 5, we’ve looked at:

With this knowledge under our belts, let’s get to this article’s topic: doing date calculations.

Creating a couple of Dates to work with

stevenotes

Let’s create a couple of Dates to work with:

  • The date and time of the Stevenote where the iPhone was introduced: January 9, 2007, 10:00 a.m. Pacific time (UTC-8), and
  • The date and time of the Stevenote where the iPad was introduced: January 27, 2010, 10:00 a.m. Pacific time (UTC-8).

Start with a fresh playground, and paste or enter the following code into it:

In the code above, we’ve created our dates in two different ways:

  • We created iPhoneStevenoteDate by setting up a DateComponents struct and then using the user’s Calendar to convert those DateComponents into a Date.
  • We created iPadStevenoteDate by converting its String representation into a Date using a DateFormatter.

Date comparisons, part 1

A chick looking at an egg.

Now that we have two Dates, let’s compare them. In Swift 5, we can use familiar comparison operators — <<===!=>>== — to tell which Date came first, or if they represent the exact (and I do mean exact) same point in time.

Add the following code to the playground and run it:

print("Did the iPhone Stevenote come BEFORE the iPad Stevenote? " +
      "\(iPhoneStevenoteDate < iPadStevenoteDate)")

print("Did the iPhone Stevenote come AFTER the iPad Stevenote? " +
      "\(iPhoneStevenoteDate > iPadStevenoteDate)")

print("Did the iPad Stevenote come BEFORE the iPhone Stevenote? " +
      "\(iPadStevenoteDate < iPhoneStevenoteDate)")

print("Does the iPad Stevenote come AFTER the iPhone Stevenote? " +
      "\(iPadStevenoteDate > iPhoneStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? " +
      "\(iPhoneStevenoteDate == iPadStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? " +
      "\(iPhoneStevenoteDate != iPadStevenoteDate)")

The output should be:

Did the iPhone Stevenote come BEFORE the iPad Stevenote? true
Did the iPhone Stevenote come AFTER the iPad Stevenote? false
Did the iPad Stevenote come BEFORE the iPhone Stevenote? false
Does the iPad Stevenote come AFTER the iPhone Stevenote? true
Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? false
Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? true

Note that these are comparisons of Dates, which measure time down to the nearest nanosecond. If you compare two Dates named date1 and date2, where date2 represents a point in time one nanosecond after date1, they will not be equal; date2 will be greater than date1.

A little later on in this article, we’ll look at more “human” ways of comparing Dates.

How far apart are the iPhone and iPad Stevenotes, part 1: In seconds, using Date’s timeIntervalSince() method

Date‘s timeIntervalSince method can give us the difference between two dates and times — in seconds.

Add the following code to the playground and run it:

print("Number of seconds between the iPhone Stevenote and the iPad Stevenote: " +
      "\(iPhoneStevenoteDate.timeIntervalSince(iPadStevenoteDate))")

print("Number of seconds between the iPad Stevenote and the iPhone Stevenote: " +
      "\(iPadStevenoteDate.timeIntervalSince(iPhoneStevenoteDate))")

The output should be:

Number of seconds between the iPhone Stevenote and the iPad Stevenote: -96249600.0
Number of seconds between the iPad Stevenote and the iPhone Stevenote: 96249600.0

The results tell us that there were 96,248,600 seconds between the iPhone Stevenote and the iPad Stevenote.

While there are cases when you’ll want to know how many seconds there are between two given points in time, there are also many cases where you’ll want to find the differences between two points in time using other units, such as days, weeks, months, and years, not to mention hours and minutes. Date‘s timeIntervalSince method isn’t going to work for these cases.

How far apart are the iPhone and iPad Stevenotes, part 2: In days, using Calendar’s dateComponents(_:from:to:) method

Most of the time, when you are calculating how far apart two given Dates are, you’ll be using this method of the Calendar struct:

dateComponents(components, from: startDate, to: endDate)

Here’s a run-down of its parameters:

Parameter Description
components Set (expressed in array notation) of Calendar.Component values specifying the time units you want, which can be:

  • .second
  • .minute
  • .hour
  • .day
  • .month
  • .year
startDate: The start Date of the time period.
endDate: The end Date of the time period.

Let’s use dateComponents(_:from:to:) to find out how many days there were between the iPhone Stevenote and the iPad Stevenote.

Add the following code to the playground and run it:

let daysBetweenStevenotes = userCalendar.dateComponents([.day],
                                                        from: iPhoneStevenoteDate,
                                                        to: iPadStevenoteDate)
print("There were \(daysBetweenStevenotes.day!) days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

The output should be:

There were 1114 days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.

In the code above, we passed dateComponents(_:from:to:) three values:

  • An array containing the Calendar.Component value .day, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of days.
  • The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

As the result tells us, there were 1,114 days between the iPhone Stevenote and the iPad Stevenote.

How far apart are the iPhone and iPad Stevenotes, part 3: In weeks

By changing the contents of the array of Calendar.Component values that we provide in the first argument of Calendar’s dateComponents(_:from:to:) method, we can get the result expressed in different time units.

Add the following code to the playground and run it:

let weeksBetweenStevenotes = userCalendar.dateComponents([.weekOfYear],
                                                         from: iPhoneStevenoteDate,
                                                         to: iPadStevenoteDate)
print("There were \(weeksBetweenStevenotes.weekOfYear!) weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

The output should be:

There were 159 weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.

In the code above, we passed dateComponents(_:from:to:) three values:

  • An array containing the Calendar.Component value .weekOfYear, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of the numbered weeks of the year on which both dates fall. For example, if event1 took place on week 2 of a year and event2 took place on week 5, the difference between the two in .weekOfYear terms would be 3.
  • The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

The result indicates that 159 weeks passed between the iPhone Stevenote and the iPad Stevenote.

If you do the math, 159 times 7 days is 1,113 days, but our previous calculation said that the iPhone Stevenote and the iPad Stevenote were 1,114 days apart. That’s because the two events are 159 whole weeks apart, plus an extra day.

How far apart are the iPhone and iPad Stevenotes, part 4: In years, months, and days

We can also put multiple values of Calendar.Component into the array that we provide as the first argument of Calendar’s dateComponents(_:from:to:) method.

Add the following code to the playground and run it:

let yearsMonthsDaysHoursMinutesBetweenStevenotes = userCalendar.dateComponents(
  [.year, .month, .day, .hour, .minute],
  from: iPhoneStevenoteDate,
  to: iPadStevenoteDate
)
let years = yearsMonthsDaysHoursMinutesBetweenStevenotes.year!
let months = yearsMonthsDaysHoursMinutesBetweenStevenotes.month!
let days = yearsMonthsDaysHoursMinutesBetweenStevenotes.day!
let hours = yearsMonthsDaysHoursMinutesBetweenStevenotes.hour!
let minutes = yearsMonthsDaysHoursMinutesBetweenStevenotes.minute!
print("There were \(years) years, \(months) months, \(days) days, \(hours) hours, and \(minutes) minutes between the the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")

In the code above, we passed dateComponents(_:from:to:) three values:

  • An array containing the Calendar.Component values .year, .month, .day, .hour, .minute, which specifies that we want the result expressed as the difference between iPadStevenoteDate and iPhoneStevenoteDate in terms of years, months, days, hours, and minutes. The method uses the largest applicable component before using smaller ones — for example, it will give results like 1 month and 5 days rather than 35 days.
  • The two dates in question, iPhoneStevenoteDate and iPadStevenoteDate.

The results show that the iPhone Stevenote and the iPad Stevenote were 3 years and 18 days apart.

Date addition, part 1: What’s the last day of a 90-day warranty that starts today?

90-day-warranty

Now that we know how to answer the question “What’s the difference in time between two Dates?”, let’s try answering a different question: “If we add a time interval to a Date, what’s the resulting Date?”

To answer this question, we’ll use this method of Calendar:

date(byAdding: timeInterval, value: numberOfTimeUnits to: startDate)

Here’s a run-down of its parameters:

Parameter Description
timeInterval dateComponents struct whose properties contain values defining the interval of time.
numberOfTimeUnits The number of timeInterval units to be added to the Date in question.
startDate The Date in question.

Let’s start with a simple bit of code that tells us the last day of a 90-day warranty whose term starts right now:

// What's the last day of a 90-day warranty that starts today?
let lastDay = userCalendar.date(byAdding: .day, value: 90, to: Date())!
print("90 days from now is: \(lastDay.description(with: Locale(identifier: "en_US")))")

The result is a Date representing a point in time 90 days from the present. On my computer, the output looked like this:

90 days from now is: Optional(“Tuesday, August 25, 2020 at 10:30:46 PM Eastern Daylight Time”)

Date addition, part 2: What was the date 5 weeks ago?

Just as we can convert addition to subtraction by adding a negative value, we can also do Date subtraction by providing date(byAdding:value:to:) with negative values. Here’s an example of code that returns a date that is an interval of time prior to the date in question:

// What was the date 5 weeks ago?
let fiveWeeksAgo = userCalendar.date(byAdding: .weekOfYear, value: -5, to: Date())!
print("5 weeks ago was: \(fiveWeeksAgo.description(with: Locale(identifier: "en_US")))")

The result is a Date representing a point in time 5 weeks in the past. On my computer, the output looked like this:

5 weeks ago was: Wednesday, April 22, 2020 at 11:12:40 PM Eastern Daylight Time

Date addition, part 3: What time will it be 4 hours and 30 minutes from now, and 4 hours and 30 minutes ago?

The date(byAdding:value:to:) method works when you just want to add one kind of time unit — a minute, hour, day, week, month, or year — to a Date. If you want to add multiple kinds of time units to a Date, such as 4 hours and 30 minutes, you need to use this Calendar method instead:

date(byAdding: timeIntervalComponents, to: startDate)

Here’s a run-down of its parameters:

Parameter Description
timeIntervalComponents dateComponents struct whose properties contain values defining the interval of time.
startDate The Date in question.

Here’s the code that answers the question “What time will it be 4 hours and 30 minutes from now?”

// What time will it be 4 hours and 30 minutes from now?
// First, we need to define a DateComponents struct representing
// a time interval of 4 hours and 30 minutes
var fourHoursThirtyMinutes = DateComponents()
fourHoursThirtyMinutes.hour = 4
fourHoursThirtyMinutes.minute = 30

// Now add the interval to the Date
let fourHoursThirtyMinutesFromNow = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes from now will be: \(fourHoursThirtyMinutesFromNow.description(with: Locale(identifier: "en_US")))")

In the code above, we did the following:

  • First, we defined a DateComponents struct representing a 4-hour, 30-minute span of time,
  • then we added that span of time to the present date and time using the date(byAdding:to:) method.

The result is a Date representing a time 4 hours and 30 seconds in the future.

Let’s find out what the Date was 4 hours and 30 seconds ago:

// What time was it 4 hours and 30 minutes ago?
var minusFourHoursThirtyMinutes = DateComponents()
minusFourHoursThirtyMinutes.hour = -4
minusFourHoursThirtyMinutes.minute = -30
let fourHoursThirtyMinutesAgo = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes ago was: \(fourHoursThirtyMinutesAgo.description(with: Locale(identifier: "en_US")))")

On my computer, the output looked like this:

4 hours and 30 minutes from now will be: Thursday, May 28, 2020 at 3:42:40 AM Eastern Daylight Time
4 hours and 30 minutes ago was: Thursday, May 28, 2020 at 3:42:40 AM Eastern Daylight Time

Date comparisons, part 2: Making Date comparisons a little more “human”

One recurring theme in science fiction (and especially in Star Trek) is the tendency for ultra-smart characters and computers to be overly, needlessly, pointlessly precise. The writers for the original series often did this with Spock, and it seemed that at least a few writers were aware of this annoying trope in later series. Here’s a bit of dialogue from The Next Generation:

Data: 6 days, 13 hours, 47 minutes.
Riker: What, no seconds?
Data: I have discovered, sir, a certain level of impatience when I calculate a lengthy time interval to the nearest second. [beat] However if you wish…
Riker: No. No. Minutes is fine.

Date‘s comparison operators have the same problem with being overly precise.

Consider the following Dates related to the announcement of SwiftUI:

  • The start of the announcement, 2 hours and 8 minutes into the WWDC 2019 keynote: June 3, 2019, 12:08:00 p.m. PDT
  • One second after the start of the announcement: June 3, 2019, 12:09:00 p.m. PDT
  • Five minutes after the start of the announcement: June 3, 2019, 12:13:00 p.m. PDT
  • Three hours after the start of the announcement: June 3, 2019, 03:08:00 p.m. PDT

Date‘s comparison operators think of all these points in time as very different, but depending on your circumstances you may think of them as being practically the same:

  • In most cases, there really isn’t a difference between the time when SwiftUI was announced and one second after.
  • If you’re concerned only with the day when SwiftUI was announced and not the exact time, there’s effectively no difference between any of the Dates listed above.

Calendar‘s compare(_:to:toGranularity) method allows us to perform Date comparisons at different levels of granularity:

compare(firstDate, to: secondDate, toGranularity: granularity)

Here’s a run-down of its parameters:

Parameter Description
firstDate The first Date in the comparison.
secondDate The second Date in the comparison.
granularity The level of precision for the comparison, expressed as an Calendar.Component value, which includes:

  • .second
  • .minute
  • .hour
  • .day
  • .month
  • .year

This is a Cocoa method named “compare”, so you’ve probably guessed that its return type is ComparisonResult. Here’s what it returns:

If… compare returns:
firstDate is earlier than secondDate, when compared at the specified granularity .orderedAscending
firstDate is equal to secondDate, when compared at the specified granularity .orderedSame
firstDate is later than secondDate, when compared at the specified granularity .orderedDescending

It’s easier to show compare(_:to:toGranularity) in action than to explain how it works. Add the following code into the playground:

// Let's define some Dates relative to the SwiftUI announcement
// (June 3, 2019, 12:08 p.m. PDT)
let swiftUIAnnouncementDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PDT"),
  year: 2019,
  month: 6,
  day: 3,
  hour: 12,
  minute: 8
)
let swiftUIAnnouncement = userCalendar.date(from: swiftUIAnnouncementDateComponents)!

let swiftUIAnnouncementPlusOneSecond = userCalendar.date(
  byAdding: .second,
  value: 1,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusFiveMinutes = userCalendar.date(
  byAdding: .minute,
  value: 5,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusThreeHours = userCalendar.date(
  byAdding: .hour,
  value: 3,
  to: swiftUIAnnouncement
)!

// This returns false, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test1 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedSame
print("test1: \(test1)")

// This returns true, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test2 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedAscending
print("test2: \(test2)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusOneSecond.
let test3 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .minute)
  == .orderedSame
print("test3: \(test3)")

// This returns true, because when measuring time at the granularity of an HOUR,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusFiveMinutes.
let test4 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusFiveMinutes,
                                 toGranularity: .hour)
  == .orderedSame
print("test4: \(test4)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncementPlusFiveMinutes happens AFTER swiftUIAnnouncement.
let test5 = userCalendar.compare(swiftUIAnnouncementPlusFiveMinutes,
                                 to: swiftUIAnnouncement,
                                 toGranularity: .minute)
  == .orderedDescending
print("test5: \(test5)")

// This returns true, because when measuring time at the granularity of a DAY,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusThreeHours.
let test6 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusThreeHours,
                                 toGranularity: .day)
  == .orderedSame
print("test6: \(test6)")

The output should be:

test1: false
test2: true
test3: true
test4: true
test5: true
test6: true

Wrapping it all up

Here’s the playground containing all the code we just worked with:

import UIKit


// Creating a couple of Dates to work with
// =======================================

// The user's calendar incorporates the user's locale and
// time zone settings, which means it's the one you'll use
// most often.
let userCalendar = Calendar.current

// Let's create a Date for the start of the Stevenote
// where the iPhone was introduced (January 9, 2007, 10:00:00 Pacific time)
// using DateComponents.
let iPhoneStevenoteDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PST"),
  year: 2007,
  month: 1,
  day: 9,
  hour: 10
)
let iPhoneStevenoteDate = userCalendar.date(from: iPhoneStevenoteDateComponents)!


// Date comparisons, part 1
// ========================

// Let's create a Date for the start of the Stevenote
// where the iPad was introduced (January 27, 2010, 10:00:00 Pacific time)
// using DateFormatter.
var dateMakerFormatter = DateFormatter()
dateMakerFormatter.calendar = userCalendar
dateMakerFormatter.dateFormat = "MMM d, yyyy, hh:mm a zz"
let iPadStevenoteDate = dateMakerFormatter.date(from: "Jan 27, 2010, 10:00 AM PST")!


print("Did the iPhone Stevenote come BEFORE the iPad Stevenote? " +
      "\(iPhoneStevenoteDate < iPadStevenoteDate)")

print("Did the iPhone Stevenote come AFTER the iPad Stevenote? " +
      "\(iPhoneStevenoteDate > iPadStevenoteDate)")

print("Did the iPad Stevenote come BEFORE the iPhone Stevenote? " +
      "\(iPadStevenoteDate < iPhoneStevenoteDate)")

print("Does the iPad Stevenote come AFTER the iPhone Stevenote? " +
      "\(iPadStevenoteDate > iPhoneStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on the EXACT SAME date and time? " +
      "\(iPhoneStevenoteDate == iPadStevenoteDate)")

print("Do the iPhone Stevenote and the iPad Stevenote fall on different dates and times? " +
      "\(iPhoneStevenoteDate != iPadStevenoteDate)")


// How far apart are the iPhone and iPad Stevenotes, part 1: In seconds,
// using Date’s timeIntervalSince() method
// =====================================================================

print("Number of seconds between the iPhone Stevenote and the iPad Stevenote: " +
      "\(iPhoneStevenoteDate.timeIntervalSince(iPadStevenoteDate))")

print("Number of seconds between the iPad Stevenote and the iPhone Stevenote: " +
      "\(iPadStevenoteDate.timeIntervalSince(iPhoneStevenoteDate))")


// How far apart are the iPhone and iPad Stevenotes, part 2:
// In days, using Calendar’s dateComponents(_:from:to:) method
// ===========================================================

let daysBetweenStevenotes = userCalendar.dateComponents([.day],
                                                        from: iPhoneStevenoteDate,
                                                        to: iPadStevenoteDate)
print("There were \(daysBetweenStevenotes.day!) days between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// How far apart are the iPhone and iPad Stevenotes, part 3: In weeks
// ==================================================================

let weeksBetweenStevenotes = userCalendar.dateComponents([.weekOfYear],
                                                         from: iPhoneStevenoteDate,
                                                         to: iPadStevenoteDate)
print("There were \(weeksBetweenStevenotes.weekOfYear!) weeks between the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// How far apart are the iPhone and iPad Stevenotes, part 4:
// In years, months, and days
// =========================================================

let yearsMonthsDaysHoursMinutesBetweenStevenotes = userCalendar.dateComponents(
  [.year, .month, .day, .hour, .minute],
  from: iPhoneStevenoteDate,
  to: iPadStevenoteDate
)
let years = yearsMonthsDaysHoursMinutesBetweenStevenotes.year!
let months = yearsMonthsDaysHoursMinutesBetweenStevenotes.month!
let days = yearsMonthsDaysHoursMinutesBetweenStevenotes.day!
let hours = yearsMonthsDaysHoursMinutesBetweenStevenotes.hour!
let minutes = yearsMonthsDaysHoursMinutesBetweenStevenotes.minute!
print("There were \(years) years, \(months) months, \(days) days, \(hours) hours, and \(minutes) minutes between the the iPhone Stevenote of 2007 and the iPad Stevenote of 2010.")


// Date addition, part 1:
// What’s the last day of a 90-day warranty that starts today?
// ===========================================================

let lastDay = userCalendar.date(byAdding: .day, value: 90, to: Date())!
print("90 days from now is: \(lastDay.description(with: Locale(identifier: "en_US")))")


// Date addition, part 2: What was the date 5 weeks ago?
// =====================================================
let fiveWeeksAgo = userCalendar.date(byAdding: .weekOfYear, value: -5, to: Date())!
print("5 weeks ago was: \(fiveWeeksAgo.description(with: Locale(identifier: "en_US")))")


// Date addition, part 3:
// What time will it be 4 hours and 30 minutes from now, and
// 4 hours and 30 minutes ago?
// =========================================================

// What time will it be 4 hours and 30 minutes from now?
// First, we need to define a DateComponents struct representing
// a time interval of 4 hours and 30 minutes
var fourHoursThirtyMinutes = DateComponents()
fourHoursThirtyMinutes.hour = 4
fourHoursThirtyMinutes.minute = 30

// Now add the interval to the Date
let fourHoursThirtyMinutesFromNow = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes from now will be: \(fourHoursThirtyMinutesFromNow.description(with: Locale(identifier: "en_US")))")

// What time was it 4 hours and 30 minutes ago?
var minusFourHoursThirtyMinutes = DateComponents()
minusFourHoursThirtyMinutes.hour = -4
minusFourHoursThirtyMinutes.minute = -30
let fourHoursThirtyMinutesAgo = userCalendar.date(
  byAdding: fourHoursThirtyMinutes,
  to: Date()
)!
print("4 hours and 30 minutes ago was: \(fourHoursThirtyMinutesAgo.description(with: Locale(identifier: "en_US")))")


// Date comparisons, part 2: Making Date comparisons a little more “human”
// =======================================================================

// Let's define some Dates relative to the SwiftUI announcement
// (June 3, 2019, 12:08 p.m. PDT)
let swiftUIAnnouncementDateComponents = DateComponents(
  timeZone: TimeZone(abbreviation: "PDT"),
  year: 2019,
  month: 6,
  day: 3,
  hour: 12,
  minute: 8
)
let swiftUIAnnouncement = userCalendar.date(from: swiftUIAnnouncementDateComponents)!

let swiftUIAnnouncementPlusOneSecond = userCalendar.date(
  byAdding: .second,
  value: 1,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusFiveMinutes = userCalendar.date(
  byAdding: .minute,
  value: 5,
  to: swiftUIAnnouncement
)!
let swiftUIAnnouncementPlusThreeHours = userCalendar.date(
  byAdding: .hour,
  value: 3,
  to: swiftUIAnnouncement
)!

// This returns false, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test1 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedSame
print("test1: \(test1)")

// This returns true, because when measuring time at the granularity of a SECOND,
// swiftUIAnnouncement happens BEFORE swiftUIAnnouncementPlusOneSecond.
let test2 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .second)
  == .orderedAscending
print("test2: \(test2)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusOneSecond.
let test3 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusOneSecond,
                                 toGranularity: .minute)
  == .orderedSame
print("test3: \(test3)")

// This returns true, because when measuring time at the granularity of an HOUR,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusFiveMinutes.
let test4 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusFiveMinutes,
                                 toGranularity: .hour)
  == .orderedSame
print("test4: \(test4)")

// This returns true, because when measuring time at the granularity of a MINUTE,
// swiftUIAnnouncementPlusFiveMinutes happens AFTER swiftUIAnnouncement.
let test5 = userCalendar.compare(swiftUIAnnouncementPlusFiveMinutes,
                                 to: swiftUIAnnouncement,
                                 toGranularity: .minute)
  == .orderedDescending
print("test5: \(test5)")

// This returns true, because when measuring time at the granularity of a DAY,
// swiftUIAnnouncement happens AT THE SAME TIME AS swiftUIAnnouncementPlusThreeHours.
let test6 = userCalendar.compare(swiftUIAnnouncement,
                                 to: swiftUIAnnouncementPlusThreeHours,
                                 toGranularity: .day)
  == .orderedSame
print("test6: \(test6)")

You can download the playground here (3KB, zipped Xcode playground file).

In the next installment, we’ll look at making working with dates and times in Swift 5 even better with with some syntactic magic.

The Dates and times in Swift 5 series

Dates and times in Swift 5Here are the articles in this series: