An attempt at a Swift really const array

gistfile1.swift

// Swift has the somewhat unusual const array semntatics in that a
// const array can still have its individual elements changed. I was thinking if there
// was a way to get the const behavior that one might expect, i.e. in a const array
// not only is the length of an array fixed, but also all of its elements.
//
// Here is my attempt:

struct ConstArray<T> {
    var array: Array<T> = []
    init(array: Array<T>) {
        self.array = array.copy()
    }
    
    subscript(index: Int) -> T {
        get {
            return array[index]
        }
    }
}

// Use this my declaring an instance of it as a const, e.g.:

let ca = ConstArray(array: [1, 2, 3])

// now:
ca[2] // give us 3
ca[1] = 3 // fails, since to subscript setting exists

// Drawbacks
// 1. It will always make a copy of the array
// 2. To guarantee immutability, you *have* to store it in a constant (i.e. use the keyword let)
// 3. Its awkward to initialize
// 4. You can't actually use it in place of where you would use a regualar array, though this could
//    potentially be fixed by implementing the Sequence protocol

Well, given that Swift now has full value semantics for arrays, this shouldn't be needed...