August 2016

changing stuff and seeing what happens

It’s how we learn best, so go forth, experiment, watch what happens, take notes — and if you can, share your knowledge. Happy hacking!

The image above comes from @ThePracticalDev’s Twitter account, and I used it in a recent article: How to work with dates and times in Swift 3, part 1: Dates, Calendars, and DateComponents.


i just want to use dates

If you’re just getting started with date and time programming in Swift 3, chances are that you probably did some Googling, found something about NSDate and its companion classes in Apple’s documentation and promptly got confused. Let me reassure you that it isn’t your fault.

For starters, a lot of the documentation out there is in Objective-C, which can throw you off if you’re not familiar with its [instance method: parameter2: parameter3:] method-calling syntax. There’s also the fact that Apple recently removed the NS prefix from Cocoa’s class names — NSDate is now just plain ol’ Date, NSCalendar is now Calendar, NSDateComponents is now DateComponents, and so on. And finally, in the move towards protocol-oriented programming, Apple has changed some classes to structs, including many of the classes for working with dates and times.

And finally, if you’re coming to Swift 3 from JavaScript, which makes do with a single object type called Date, the idea of having this set of classes just to handle dates and times looks like overkill:

swift 3 date and time classes

Click the diagram to see it at full size.

In this series of articles, we’ll look at date and time programming in Swift 3. By its end, you’ll have a firm grasp on the topic.

Swift’s Date struct represents dates and times

swift date struct

Click the diagram to see it at full size.

In Swift, dates and times are represented by instances of Date, which is a struct. Date is independent of any time zone, or even any calendar system. It gets this independence through the way it represents time: as a number of seconds relative to the start of the Third Millennium, January 1, 2001, 00:00:00 UTC.

The following playground code shows the various ways of creating Dates:

Of course, we don’t think of dates and times in terms of seconds relative to the start of the Third Millennium, or the start of the Unix Epoch, or any other arbitrary date and time. That’s why Swift features a couple of other structs to help us make sense of Dates: Calendar and DateComponents.

Calendars give dates context, DateComponents let us assemble dates or break dates apart

swift calendar struct

Click the diagram to see it at full size.

Think of the Calendar struct as a way to view Dates in a way that makes more sense to us: not as a number of seconds before or after January 1, 2001 00:00:00 UTC, but in terms of a year, month, day, hour, minute, and more.

The Calendar struct supports 16 different calendar systems, including the Gregorian calendar (a.k.a. the Western or Christian calendar), which is likely the one you use the most. Consider Swift’s reference date:

  • In a Date struct, its value is 0.
  • In the Gregorian calendar, this date has the following values:
    • Year: 2001
    • Month: 1
    • Day: 1
    • Hour: 0
    • Minute: 0
  • In the Hebrew calendar, this date has the following values:
    • Year: 5761
    • Month: 4
    • Day: 6
    • Hour: 0
    • Minute: 0
  • In the Buddhist calendar, this date has the following values:
    • Year: 2543
    • Month: 1
    • Day: 1
    • Hour: 0
    • Minute: 0

In most apps, you’ll likely be using the Gregorian calendar, so Calendar‘s real use is to convert Dates into DateComponents, and DateComponents into Dates:

swift datecomponents struct

Click the diagram to see it at full size.

The DateComponents struct is an assembly of properties that make up a date, such as year, month, date, hour, minute, second, and so on. DateComponents instances can be used to represent either a specific point in time, or a duration of time.

Using both Calendar and DateComponents structs, we can perform these key actions:

  • Build Dates using properties such as year, month, day, hour, and minute rather than a number of second relative to a reference date, and
  • extract properties from Dates, such as year, month, day, hour, and minute.

Let’s start creating some Dates with the help of Calendar and DateComponents.

Let’s create a Date given a year, month, and day, part 1

alexander graham bell

Let’s start with the first date in phone history: March 10, 1876, the day when Alexander Graham Bell made the first phone call. Create a new playground and enter or paste the code below:

In the code, we:

  • Get the user’s current Calendar.
  • Create an DateComponents struct, firstLandPhoneCallDateComponents, providing values for the year, month, and day parameters, and nil for all the others.
  • Use the user’s Calendar to create firstLandPhoneCallDate using firstLandPhoneCallDateComponents.
  • Get the internal representation of the Date.

Here’s a screenshot of the playground code as seen on my computer, whose time zone is set to “US/Eastern” (UTC-5):


Click the screenshot to see it at full size.

Note the results in the sidebar at the lower right-hand corner:

  • firstLandPhoneCallDate‘s value corresponds to the DateComponents properties we set: March 10, 1876, 12:00 a.m..
  • firstLandPhoneCallDate‘s internal value, contained within its timeIntervalSinceReferenceDate property, is -3,938,697,748, which indicates that Alexander Graham Bell’s inaugural phone call was made nearly 4 billion seconds prior to the start of the Third Millennium.

Let’s create a Date given a year, month, and day, part 2

martin cooper

Let’s try creating another momentous date in phone history: the day when Martin Cooper made the first cellular phone call, April 3, 1973. We’ll do it differently this time, by creating a blank DateComponents struct, and then setting its year, month, and day properties. Add the following code to the code above:

In the code, we:

  • Create an empty DateComponents struct, firstCellPhoneCallDateComponents.
  • Set the year, month, and day properties of firstCellPhoneCallDateComponents to correspond to the date April 3, 1973.
  • Use the user’s Calendar to create firstCellPhoneCallDate using firstCellPhoneCallDateComponents.
  • Get the internal representation of the Date.

Here’s a screenshot of the results:


Click the screenshot to see it at full size.

Let’s create a Date: What date does National Donut Day — the first Friday in June — fall on in 2017?

Having come from Canada, the country with the world’s highest per capita donut shop concentration and the people who eat the most donuts per capita, I can assure you that National Donut Day has been a real thing since 1938. It takes place on the first Friday in June, and we can find out what date it falls on in 2017 — or any other year — through the judicious use of DateComponents properties.

Add the following code to the current playground:

You should be familiar with the year and month DayComponents properties by now, and we’re using a couple that may be new to you:

  • weekday: Specifies a day of the week. With the Gregorian calendar, valid values are 1 through 7, where 1 is Sunday, 2 is Monday, 3 is Tuesday, and so on. Since we’re looking for a Friday, we’ve set this value to 6.
  • weekdayOrdinal: Specifies the order of the given weekday in the next larger specified calendar unit. Since we set weekday to 6 and set this value to 1, and since the next largest specified calendar unit was month, we’ll get the date of the first Friday of the month.

If you check the value of donutDayDate in the playground’s sidebar, you should see Jun 2, 2017, 12:00 AM. If you look at a calendar, you’ll confirm that it is indeed the first Friday of June 2017.

changing stuff and seing what happens

In the spirit of the fake book cover shown above, let’s see what happens if we don’t specify the month. Comment out the following line from the code you just added…

donutDayComponents.month = 6

…so that the code now looks like this:

When you run the code, you’ll see that the date for donutDayDate is now Jan 6 2017, 12:00 AM. Now that we’re specifying only a year and not a month, Swift interprets the combination of donutDayComponents.weekday = 6 and donutDayComponents.weekdayOrdinal = 1 to mean “the first Friday of the year”. If you look at a calendar, you’ll confirm that January 6, 2017 is indeed the first Friday of the year.

Let’s create one more Date: on Thursday of the 18th week of 2017…in Tokyo.

The great thing about Swift’s Calendar class is that it does its best to work with the DateComponents that you give it, and DateComponents gives you all sorts of ways to specify a date. Let’s assume for a moment that you’re in Japan and want to leave work at the ridiculously early hour of 5 p.m. and have some relaxing Suntory times, and it just happens to be the 18th week of 2017. What’s the date?

The answer comes from this code:

On my system, which is in the Eastern daylight time zone (UTC-4) at the time of writing, thursday5pm18thWeek2017TokyoDate displays as May 4, 2017, 4:00 AM in my playground’s sidebar, and looking at a calendar confirms that May 4th is indeed the Thursday of the 18th month of 2017.

Let’s extract DateComponents from a Date, part 1

Now that we’ve created some Dates using DateComponents, let’s do the reverse and extract DateComponents from given Dates. We’ll continue with our playground and use a Date we’ve already created: firstLandPhoneCallDate, which corresponds to the date of Alexander Graham Bell’s historic phone call, March 10, 1876. Here’s code that extracts the year, month, and day from this Date:

Let’s extract DateComponents from a Date, part 2

This time, let’s create a new Date — one that corresponds to this key date in iOS history: the “Stevenote” where the original iPhone was first announced:

If you were to ask Swift when this Stevenote took place, it would reply “190,058,400 seconds after the reference date”. For most of us, this is a meaningless figure, so we’ll extract the following DateComponents from this Date:

  • Year
  • Month
  • Day
  • Hour
  • Minute
  • What day of the week this Date fell on
  • What week of the year this Date fell on

Here’s the code:

Let’s extract DateComponents from a Date, part 3

Let’s try it again with another key iOS date — the Stevenote where the original iPad was announced:

This time, if you were to ask Swift when this Stevenote took place, it would reply “286,308,000 seconds after the reference date”. Let’s get all the DateComponents for this date:

Let’s take a look at each DateComponents property and what it represents:

Property Description
calendar The calendar system for the date represented by this set of DateComponents. We got these DateComponents by converting a Date using a Gregorian Calendar, so in this case, this value is gregorian.
day The day number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 27.
era The era for this particular date, which depends on the date’s calendar system. In this case, we’re using the Gregorian calendar, which has two eras:

  • BCE (a.k.a. BC), represented by the integer value 0
  • CE (a.k.a. AD), represented by the integer value 1
hour The hour number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 13, because in my time zone, 18:00:00 UTC is 13:00:00.
minute The minute number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 0.
month The month number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 1.
nanosecond The nanosecond number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 0.
quarter The quarter number of this particular date and time. January 27, 2010, 18:00:00 UTC, is in the first quarter of the year, so this value is 0.
second The second number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 0.
timeZone The time zone of this particular date and time. I’m in the UTC-5 time zone (US Eastern), so this value is set to that time zone.
weekday The day of the week of this particular date and time. In the Gregorian calendar, Sunday is 1, Monday is 2, Tuesday is 3, and so on. January 27, 2010, was a Wednesday, so this value is 4.
weekdayOrdinal The position of the weekday within the next larger specified calendar unit, which in this case is a month. So this specifies nth weekday of the given month. Jauary 27, 2010 was on the 4th Wednesday of the month, so this value is 4.
weekOfMonth The week of the month of this particular date and time. January 27, 2010 fell on the 5th week of January 2010, so this value is 5.
weekOfYear The week of the year of this particular date and time. January 27, 2010 fell on the 5th week of 2010, so this value is 5.
year The year number of this particular date and time. For January 27, 2010, 18:00:00 UTC, this value is 2010.
yearForWeekOfYear Oh wow, this is so hard to explain that I’ll leave it to Apple’s docs.

Wrapping it all up

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

In the next installment, we’ll look at converting Dates to Strings, and vice versa.


The truth about typefaces

by Joey deVilla on August 10, 2016


This one goes out to all the front-end and interface designers and developers out there.


raspberry pi 12

Click the photo to see it at full size.

On the most recent Amazon Prime Day — an annual trick that Amazon pulls in order to boost sales in the same vein as Cyber Monday, but in the summer — I managed to limit myself to buying just one sale-priced thing that I didn’t really need: the CanaKit Raspberry Pi 3 Complete Starter Kit. It normally sells on Amazon for US$75, but it was on sale that day for US$60.

The Raspberry Pi 3 is the current version of a series of single-board computers about the size of a deck of playing cards, and are:

I plan to use the Raspberry Pi to make some initial delving into IoT (Internet of Things) development, and as part of my journey into developing for that category of computer that I call “tiny and shiny” — smartphones, tablets, and now Raspberry Pi / Arduino-type boards.

Here’s the CanaKit Raspberry Pi 3 Complete Start Kit box:

raspberry pi 01

When I opened it, I saw this:

raspberry pi 02

The first thing you should see is a greeting card that also provides an email address for assistance, should you need it. The other side of the card has a diagram explain what each of the GPIO interface pins on the Raspberry Pi 3 board is for.

Below the card was an HDMI cable:

raspberry pi 03

And below that were three boxes:

raspberry pi 04

From largest to smallest, the three boxes contained the Raspberry Pi 3 board and SD card (which functions as its “hard drive”)…

raspberry pi 05

…a case for the board…

raspberry pi 06

…and a power supply for the board:

raspberry pi 07

Below the boxes were these items:

raspberry pi 08

One bag contained a USB microSD card reader. It allows you to use your regular computer to download updated or different versions of the Raspberry Pi OS or software and transfer them onto the microSD card:

raspberry pi 09

The other bag contained two heatsinks for its chips. They already have heatsink adhesive attacked to them; you just have to peel off the backing and stick them onto their respective chips:

raspberry pi 10

At the bottom of the box was the “quick start” guide:

raspberry pi 11

Here’s the board mounted in the lower tray portion of the case:

raspberry pi 13

And here’s the board with the middle section of the case attached:

raspberry pi 14

And here’s what the Pi looks like once the case is assembled:

raspberry pi 15

Assembling the case is pretty easy, as no tools are required. It simply snaps together.

Here’s the case on my desk, placed beside a $20 bill for size comparison:

raspberry pi 16

The Pi case is smaller than the hard drive that I connected to it (you can see it below the Pi):

raspberry pi 18

I decided to take the beginner route and start up the system using NOOBS, short for “New out of the box software”. It came pre-loaded onto the SD card that came with the board, and it installed Raspbian, the official supportedRaspberry Pi OS, and based on Debian. Once the OS is installed, here’s what you see when you boot up the Pi:

raspberry pi 19

Once it finishes booting up, you’re taken to a GNOME desktop:

raspberry pi 20

I used to have a stack of USB keyboards, but I’d given most of them away to friends and family, and my last couple are still back in Toronto. Figuring that I’d end up taking the Pi to meetups, BarCamps, and other demo sessions, or perhaps use it as a living room media center / internet device, I went with the Logitech K400 all-in-one keyboard, shown below. It’s currently on sale at Walmart for US$20:

raspberry pi 21

And thanks to Anastasia Sistevaris, an intern at Wiley, I got hooked up with a set of Raspberry Pi books, the first of which arrived recently: Exploring Raspberry Pi by Derek Molloy. I’ll do a writeup of this book in a later article:

raspberry pi 22

Watch this space for more Raspberry Pi articles as I start noodling with my new toy!


ron and arlene klein at next money tpa

Click the photo to see it at full size.

Last night, I had the pleasure of meeting inventor Ron Klein and his wife Arlene, at the Next Money TPA meetup. If you’re a reader of this blog, it’s likely that you’ve used at least one of his innovations:

  • The MLS — as in multiple listing service — for real estate,
  • Interactive voice response for banks,
  • a bond monitoring system for Wall Street traders…

…and then there’s the innovation you’ve most likely used — automated validation of credit cards through the use of a magnetic stripe:

He was also an artillery forward observer in the Korean War, where he went on 58 missions. He got hurt during the last one, resulting in a spinal injury, and earning him a Purple Heart. The injury caused him painful spinal stenosis, where the bones in his spine put pressure the spinal cord and related nerves leading from it. He took up exercise, which he found was pain-relieving, and does it so often that he’s participated and won medals in the Florida Senior Games.

ron klein with bike

In the bad old days, credit card validation was done manually. Any merchant that accepted payments via credit card was given a long paper list of “bad” credit card numbers, and would have to “eyeball” the list in order to valid a credit card. I remember when this sort of thing was still done in the early 1970s, and it was slow even under the best of circumstances, never mind during big sales or something like Black Friday.

Klein, then director of engineering for Ultronics Systems Corporation — which would later become part of GT&E Financial — developed a “validity-checking system”, which allowed merchants to enter credit card numbers into a “desk-mountable interrogation unit” that could check against a central store of credit card numbers which would be stored in drum memory. If the account number on the card wasn’t on the “bad” list, the desk unit would show a “credit good” light; otherwise, it would display an error signal.

According to, Klein’s original design for the verifier was such that a bad credit card would be held by the device. “If the credit wasn’t good,” he said, “it locked up the card so that the person didn’t get the card back, because the merchant got credit for capturing negative-account cards.”

At the age of 81, Ron could simply enjoy a quiet retirement, but that’s not his style. “I took three months off, but I got bored,” he said. “I’d rather keep busy, taking on new challenges. I’m not empty yet!”

He spoke to the group for about 90 minutes, regaling us with stories about his childhood, the business world, and his drive to find solutions to problems.

One theme he kept repeating to the meetup group was to simplify. “There’s a fix for everything, a solution for every challenge. The trick is to simplify. Identify the problem, simplify, then be smart, daring, and different.”

Another bit of advice he gave to the group was to “Be a smiling cobra, and never point an unloaded gun,” which I took to mean be nice as much as you can, but be tough when you have to — and mean it. I found him to be quite affable, but if he managed to operate in the world of Wall Street, I can he his need to be a cobra from time to time.

ron and arlene 2

His last bit of advice to the group was to “sell the benefit, not the idea”. This is a good reminded for anyone who’s inventing a product or service — nobody cares about inventions for their own sake, but the benefits they provide. This may seem obvious to some, but as I like to say, there’s great power in stating the obvious.

Ron lives in Sarasota, about an hour and a quarter south of my place. I may have to drive down there sometime, take him and Arlene out to lunch, just so I can hear more stories about the things he created — and is still creating. My thanks to Ron and Arlene for appearing at the Next Money TPA meetup!

next money tpa

Next Money TPA is the Tampa chapter of Next Money, an international group of fintech communities, and the meetup group that brought Ron Klein to speak. Next Money TPA brings together people from the Tampa Bay area to discuss the intersection of finance, technology, design, and creative spaces. Organized by Bruce Burke, the meetup invites “casual, entrepreneurial, inquisitive minds” to gather, share ideas, and meet each other.