Two-Phase Initialization in Swift

One then another

Photo by Vincent van Zalinge on Unsplash

I’ve previously written about Swift initializers, however I didn’t EVEN MENTION Two-Phase Initilization.

Time to put that right!

Difficulty: Beginner | Easy | Normal | Challenging
This article has been developed using Xcode 11.5, and Swift 5.2.4

Prerequisites:

• You need to either be able to make a Single View Application in Swift, or use a Playground.

What is Swift’s Two-Phase Initialization

Swift has many safety features that allow us to have a great experience programming.

So what has Swift done to ensure that properties are set before a class (or indeed a struct) is ready for use?

The answer is the aforementioned Two-Phase Initialization: Two-phase initialization prevents property values from being accessed before they are are initialized, and prevent the property values from being set to a different value by another initializer unexpectedly.

The safety checks

Safety check 1

All properties introduced by it’s class are initalized before it delegates up to a superclass initializer.