Thursday, July 26, 2018 [Tweets] [Favorites]

Conditional Compilation in Swift

Dave DeLong:

Settings in configuration files can be configured to have different values based on certain conditions (namely, the name of the SDK being used and/or the architecture being built).

This, combined with a certain build setting, gives us everything we need to have nicer conditional compilation.

[…]

Now we have something that’s much clearer and future-proof:

func isFeatureAvailable() -> Bool {
    #if BUILDING_FOR_SIMULATOR
        return false
    #else
        return true
    #endif
}

This uses the SWIFT_ACTIVE_COMPILATION_CONDITIONS build setting.

Dave DeLong:

Buried deep inside the Xcode Build Settings reference is a pair of obscure build settings: INCLUDED_SOURCE_FILE_NAMES and EXCLUDED_SOURCE_FILE_NAMES.

As their names suggest, these build settings allow you to specify additional files via your build configurations. When compiling, the exclusions happen first, and then the inclusions are applied, resulting in a final set of files passed to the compiler.

The values to these settings can be explicit paths to files, or they can be glob patterns (like *.swift). Since this is a build configuration file, substitutions work too: *.$(CURRENT_ARCH).c. And finally, since these are regular build settings, we can conditionalize the value based on the SDK.

He uses these to match platform qualifiers in the directory and filenames.

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