Notice: Undefined index: understanding-swift in /var/sites/ on line 89
Why would you want to create an empty collection? - a free tutorial

NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

Why would you want to create an empty collection?

Paul Hudson    @twostraws   

When you’re just learning Swift, it’s common to see examples such as this one:

let names = ["Eleanor", "Chidi", "Tahani", "Jianyu", "Michael", "Janet"]

That’s a constant array of six strings, and because it’s constant it means we can’t add more things to the array – we know all our items when the array is created, so the rest of our program is just using that fixed data.

But sometimes you don’t know all your data up front, and in those cases it’s more common to create an empty collection then add things as you calculate your data.

For example, we have our fixed names array above, and if we wanted to figure out which names started with J then we would:

  1. Creating an empty string array called something like jNames
  2. Go over every name in the original names array and check whether it starts with “J”
  3. If it does, add it to the jNames array.

When we’ve gone over all the names, we’ll end up with two strings in jNames: Jianyu and Janet. Of course, if our check was which names started with “X” then we’d end up with no names in the array – and that’s OK. It started as empty and ended as empty.

Later on in this book we’ll be looking at the Swift code needed to make all this work for real.

Hacking with Swift is sponsored by NSSpain

SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!

Find out more

Sponsor Hacking with Swift and reach the world's largest Swift community!

Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Link copied to your pasteboard.