One common use of build configurations is to hardcode behavioral settings in your application. This is done using preprocessor directives.
In Xcode, select the project in the project navigator to bring up the project editor. In the project editor, select the RanchForecastSplit target and switch to the Build Settings tab. Scroll nearly to the bottom until you find the Swift Compiler - Custom Flags heading, where you will see the Other Swift Flags field (Figure 36.3).
Figure 36.3 Other Swift flags
Expand that field, using the disclosure arrow on the ...