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341
ViewsSwift errors using #if, #endif
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.
3 answers
Answer question0
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 ...
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As @user28434 notes, there is no source-level pre-processor. This has gotten rid of a lot of very tricky pre-processor problems in C (such as bizarre needs for parentheses to make things work).
However, #if is integrated well into the language, and specifically supports switch for exactly these kinds of cases.
var a = 0
#if DEBUG
let b = 0
#endif
switch a {
case 7: a += 1
#if DEBUG
case b: a += 2
#endif
case 5: a += 3
default:
break
}
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You can simply achieve this case with below code:
if a == b {
#if DEBUG
a += 2
#else
a += 1
#endif
} else if a == c {
a += 3
}