Swift: Use constant property to define another property fails - swift

Question

I'm trying to declare an array of a static size. I'd like a constant to define the size of the array.
I'm trying the following in Swift
class foo {
let size = 10
let myArray = [Int](count: size, repeatedValue: 0)
}
But this fails with an error,
'foo.Type' does not have a member named 'size'
If I don't use the size constant, the compiler is happy with it but isn't what I'd like. And there's no #define capability that I'm aware of.
let myArray = [Int](count: 10, repeatedValue: 0)

Answer 1

Swift gives you a couple ways to do this. The simplest, and most in line with the #define style you mention, is to declare size as a global constant:
let FOOSIZE = 10
class Foo {
let myArray = [Int](count: FOOSIZE, repeatedValue: 0)
}
Alternatively, you can define myArray as a lazy variable, and use a closure to populate its value. By the time the closure is executed you'll be able to access self.size:
class Foo {
let size = 10
lazy var myArray: [Int] = { [Int](count: self.size, repeatedValue: 0) }()
}

Answer 2

In swift self is unavailable until all class/struct properties have been initialized, and a subclass initializer has been called (in case of an inherited class).
In your case you are initializing properties outside of an initializer, but that doesn't change the result: you cannot initialize a variable implicitly referencing self (which you do when accessing to the size property).
However, size looks like a constant, and as such it's better to instantiate it once (as a static property) rather than having it created in each class instance. Swift doesn't support static class properties, but structs do, so a trick is to define an inner private struct, containing the static immutable properties you may need:
class foo {
private struct Static {
static let size = 10
}
let myArray = [Int](count: Static.size, repeatedValue: 0)
}

Answer 3

With Swift 1.2 you can simply add static before let size, making it a class constant and as such defined before myArray is being defined:
class foo {
static let size = 10
let myArray = [Int](count: size, repeatedValue: 0)
}
Be aware though, that using size later in your code requires you to fully qualify it as foo.size.

Answer 4

One way is for it to be in a function. This worked in a playground:
import UIKit
class ViewController: UIViewController {
var myArray = [Int]()
func appendArray (#index: Int, value: Int) {
myArray[index] = value
}
override func viewDidLoad() {
super.viewDidLoad()
let size = 10
myArray = [Int](count: size, repeatedValue: 0)
appendArray(index: 3, value: 4)
println(myArray)
}
}
Okay, I used a ViewController because it was convenient, but not necessary. No problem declaring the array out side of a function. I still used a function to create the array and used another one t change a value.