Swift Conditional Compilation

Check for the presence of a flag for conditional compilation in Swift using #if #else #endif.

Set the symbol in the Xcode Project Build Settings under

Swift Compiler - Custom Flags - Other Swift Flags.

Usage: For example, using -D DEBUG

#if DEBUG
    println("debug build")
#else
    println("not a debug build")
#end

To set multiple symbols: For example, DEBUG and STAGING can both be set with -D DEBUG -D LEGACY. Both symbols must be prefaced with the -D option.

Found here