Error in Swift class: Property not initialized at super.init call
Quote from The Swift Programming Language, which answers your question:
“Swift’s compiler performs four helpful safety-checks to make sure that two-phase initialization is completed without error:”
Safety check 1 “A designated initializer must ensure that all of the “properties introduced by its class are initialized before it delegates up to a superclass initializer.”
Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itunes.apple.com/us/book/swift-programming-language/id881256329?mt=11
Swift has a very clear, specific sequence of operations that are done in initializers. Let's start with some basic examples and work our way up to a general case.
Let's take an object A. We'll define it as follows.
class A {
var x: Int
init(x: Int) {
self.x = x
}
}
Notice that A does not have a superclass, so it cannot call a super.init() function as it does not exist.
OK, so now let's subclass A with a new class named B.
class B: A {
var y: Int
init(x: Int, y: Int) {
self.y = y
super.init(x: x)
}
}
This is a departure from Objective-C where [super init]
would typically be called first before anything else. Not so in Swift. You are responsible for ensuring that your instance variables are in a consistent state before you do anything else, including calling methods (which includes your superclass' initializer).