Notice: Undefined index: understanding-swift in /var/sites/hackingwithswift.com/site/src/Controller/NewBooksReadController.php on line 89
Why does Swift have dictionaries as well as arrays? - a free tutorial

NEW: Start my new Ultimate Portfolio App course with a free Hacking with Swift+ trial! >>

Why does Swift have dictionaries as well as arrays?

Paul Hudson    @twostraws   

Dictionaries and arrays are both ways of storing lots of data in one variable, but they store them in different ways: dictionaries let us choose a “key” that identifies the item we want to add, whereas arrays just add each item sequentially.

So, rather than trying to remember that array index 7 means a user’s country, we could just write user["country"] – it’s much more convenient.

Like sets, dictionaries don’t store our items with a specific order, so they optimize the way they store items for fast retrieval. So, when we say user["country"] it will send back the item at that key (or nil) instantly, even if we have a dictionary with 100,000 items inside.

Unlike tuples, you can’t be guaranteed that a key in a dictionary exists. This is why reading a value from a dictionary might send back nothing – you might have requested a key that doesn’t exist!

Hacking with Swift is sponsored by ViRE

SPONSORED ViRE offers discoverable way of working with regex. It provides really readable regex experience, code complete & cheat sheet, unit tests, powerful replace system, step-by-step search & replace, regex visual scheme, regex history & playground. ViRE is available on Mac & iPad.

Download on the App Store

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

BUY OUR BOOKS
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!

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.