How to avoid "Variable j written into, but never read" in Swift?

Question

I am using variable j to print its final value inside a defer block as shown below:

func justForFun()
{    
   defer {let x = j; print("\(x)")}
   var j = 0
   for i in 1...5
   {
       print("\(i)")
       j = i*2;
   }
}
justForFun()

So, the variable j is indeed read and printed inside the defer block. Still, PlayGround displays the warning that variable j is written, but never read. Is there a way to enlighten the compiler and to rid this warning?

Answer 1

The warning disappears if the variable declaration is moved above the defer.

$ cat d.swift 
func justForFun() {    
   var j = 0
   defer {let x = j; print("\(x)")}
   for i in 1...5 {
       print("\(i)")
       j = i*2;
   }
}
justForFun()

$ swift d.swift 
1 
2
3
4
5
10

While this doesn't explain why the warning appears, it does answer how you can make the warning go away.

As far as enlightening the compiler, I don't think you can do that. You might want to file and issue at swift.org; see this page for how to report a bug. It seems the static flow checker is not looking at defer statements, which I believe it should. Good find.