Conditionally-compiled case statement in swift

Question

I've implemented an enum statement in Swift with computed properties. I want to add values that are conditionally compiled, e.g. only for certain configurations.

Here is an example of what I'm trying to do:

enum Rows: Int
{
    case Row1
    case Row2
    #if DEBUG
    case Debug
    #endif

    var rowTitle: String
    {
        case Row1: return "Row 1"
        case Row2: return "Row 2"
        #if DEBUG
        case Debug: return "Debug"
        #endif
    }
}

This does't seem to be supported as I get the following error message on the case statement within the switch statement:

'case' label can only appear inside a 'switch' statement

Is there a way to do this in Swift?

Thanks,
David

Christopher Whidden · Accepted Answer · 2017-11-05 03:58:41Z

2

Conditional compilation of enum cases now works as of Swift 4.

enum Foo {
    case bar

    #if DEBUG
    case baz
    #endif
}

let bar = Foo.bar

#if DEBUG
let baz = Foo.baz
#endif

answered Nov 5, 2017 at 3:58

Christopher Whidden

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Comments

olivaresF · Accepted Answer · 2016-03-28 17:47:48Z

2

This is a known bug in Swift. There's no way to currently do conditional compiling inside a switch.

answered Mar 28, 2016 at 17:47

olivaresF

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Comments

Mike Taverne · Accepted Answer · 2015-01-20 01:45:38Z

0

Your syntax for conditional compilation looks correct. However, when I paste your code into a playground, I get multiple errors. The first is at the line beginning with var rowTitle, and the error is "Enums may not contain stored properties".

answered Jan 20, 2015 at 1:45

Mike Taverne

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3 Comments

David Potter Over a year ago

Sorry, the equal sign shouldn't have been there. The syntax should now be correct.

Mike Taverne Over a year ago

Yes, so now the issue is that you are using case inside a property definition, not inside a switch statement. You can't do that. The issue is not with the conditional compilation.

David Potter Over a year ago

I'm confused. How is the case inside a property definition? Is #if DEBUG actually a form of a closure declaration?

Matteo Piombo · Accepted Answer · 2015-01-20 09:47:21Z

0

This is a version of your code that is syntactically correct for the implementation of the computed variable rowTitle:

enum Rows: Int
{
    case Row1
    case Row2

    var rowTitle: String {
            switch self {
            case Row1:
                return "Row 1"
            case Row2:
                return "Row 2"
        }
    }
}

Said that, this is probably what you meant in your question ... but does not work:

enum Rows: Int
{
    case Row1
    case Row2
    #if DEBUG
    case Debug
    #endif

    var rowTitle: String {
        switch self {
        case Row1:
            return "Row 1"
        case Row2:
            return "Row 2"
        }
        #if DEBUG
            switch self {
            case Debug:
            return "Debug"
            default:
            break
            }
        #endif
    }
}

The compiler will not give you any error, but you will not be able to use the Debug case.

answered Jan 20, 2015 at 9:47

Matteo Piombo

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1 Comment

David Potter Over a year ago

The first example you gave is correct if I don't want any conditionally-compiled cases. The second example won't compile because the first switch isn't exhaustive. Also, I want to avoid default cases because I want the compiler to give me an error if I add a new case but forget to handle it in the switch statement.

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