How to check if code is in DEBUG or RELEASE build in Swift

When developing an app, there might be a time when you want to add some code during development (DEBUG build configuration) and remove it from the release version (RELEASE build configuration) for security and performance reasons.

You can easily do that with the help of Conditional Compilation Block and Compilation Conditions.

Conditional Compilation Block

A conditional compilation block allows code to be conditionally compiled depending on the value of compilation conditions.

It has the following format.

#if compilation condition
  // statement
#endif

Or

#if compilation condition 1
  // statement 1
#elseif compilation condition 2
  // statement 2
#else
  // statement 3
#endif

As you can see, it has a similar format as an if-else statement. The main difference is the compilation condition is evaluated at compile time.

As a result, only one statement is compiled and executed at compile time.

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Compilation conditions

Compilation condition is quite a fancy name, but you can think of it as a boolean value that can be read at a compile time.

How to check if code is in DEBUG or RELEASE mode in Swift

If we have a boolean value that returns true when code runs in the Debug configuration, we can use Conditional Compilation Block to compile the code based on that value.

Luckily, Xcode already provides the compilation condition that does just that. Xcode named this value DEBUG.

So, you can check if the code is in Debug configuration with the following code.

#if DEBUG
    print("Debug")
#else
    print("Release")
#endif

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How to add new Compilation conditions

The way that we define compilation conditions for Swift is by declaring it in the "Active Compilation Conditions" field.

Active Compilation Conditions are located in the project Build Settings. Here is how to find them.

1. Select the root of the project from the Project Navigator.
2. Select the current project (Not the target).
3. Select Build Settings tab.
4. Then, you will see the "Active Compilation Conditions" field under the "Swift Compiler - Custom Flags" section.

To add, edit, or remove compilation conditions.

1. Double-click on the value field on the configuration you want to modify.
2. You will see a popup containing all compilation condition values.
3. Double-click on the value that you want to edit. You can also click on a plus (+) and minus (-) button to add or remove a value.