Swift errors using #if, #endif

Question

Using #if, #endif in Swift (using Xcode) produces errors if it cuts into the flow of an operation. This screenshot says it all:

Does anyone know a solution to make this example work, without repeating the entire code block twice? There can easily be situations where the entire block can be very large.

EDIT: My sample was a bit too simple. Here is a new sample where the "else if" depends on the same define (DEBUG). The "else if" must also be within the #if and #endif. And other samples can be much more complex than this.

Answer 1

Ideally, limit the usage of #if as much as possible. Using preprocessor directives is always a bit of a code smell. In this case, you can simply use a boolean variable:

#if DEBUG
let debug = true
#else
let debug = false
#endif

Then simply use the variable:

var a = 0
var b = 0

...

else if debug && a == b {
}

In release mode the code will become unreachable and the optimizer will remove it anyway.

With a bit of imagination, we can find other solutions, for example, we can move the check to a function:

func isDebugCheck(a: Int, b: Int) -> Bool {
   #if DEBUG
      return a == b
   #else
      return false
   #endif
}

or we can move the whole code to a separate function and replace if-else by a return (or continue, depending on you needs), e.g.:

if a == 7 {
  ...
  return
}

#if DEBUG
  if a == b {
     return
  }
#endif

if ...