swift if debug not working

下面代码不起作用：

#if DEBUG let a = 2 #else let a = 3 #endif

Now, you must set the “DEBUG” symbol elsewhere, though. Set it in the “Swift Compiler - Custom Flags” section, “Other Swift Flags” line. You add the DEBUG symbol with the -D DEBUG entry.

As usual, you can set a different value when in Debug or when in Release.

I tested it in real code and it works; it doesn’t seem to be recognized in a playground though.

You can read my original post here.

IMPORTANT NOTE: -DDEBUG=1 doesn’t work. Only -D DEBUG works. Seems compiler is ignoring a flag with a specific value.

参考：

http://stackoverflow.com/questions/24003291/ifdef-replacement-in-swift-language