I'd like a function to return a reference of an array:
var a = [1, 2]
var b = [3, 4]
func arrayToPick(i:Int) -> [Int] {
return i == 0 ? a : b
}
inout var d = arrayToPick(0)
d[0] = 6
println(a[0]) // 1
println(d[0]) // 6
I'm unable to return &a or &b in arrayToPick because those can't be casted to [Int].
How to return a reference on a or b from a function?
You cannot return inout value. Because the compiler cannot guarantee the lifetime of the value.
You have unsafe way, like this:
var a = [1, 2]
var b = [3, 4]
func arrayToPick(i:Int) -> UnsafeMutablePointer<[Int]> {
if i == 0 {
return withUnsafeMutablePointer(&a, { $0 })
}
else {
return withUnsafeMutablePointer(&b, { $0 })
}
}
var d = arrayToPick(0)
d.memory[0] = 6
println(a[0]) // -> 6
In this case, after a is deallocated, d.memory access may cause BAD_ACCESS error.
Or safe way, like this:
var a = [1, 2]
var b = [3, 4]
func withPickedArray(i:Int, f:(inout [Int]) -> Void) {
i == 0 ? f(&a) : f(&b)
}
withPickedArray(0) { (inout picked:[Int]) in
picked[0] = 6
}
println(a[0]) // -> 6
In this case, you can access the picked value only in the closure.
struct to be always by value and class to be always by reference. For an even stranger reason - an array is a struct. Someone should have told them about the operator & and move semantics.
