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How to check whether a module is available using canImport()

Swift version: 5.4

Paul Hudson    @twostraws   

Writing multi-platform code has its own challenges, but if you use the canImport() compiler test then one big challenge is solved for you: you can write one chunk code to run if a specific module is available, and another chunk otherwise.

For example, this code will check for UIKit, AppKit, and all other possibilities so that you can pick whichever color type is best for the current platform:

#if canImport(UIKit)
// iOS, tvOS, and watchOS – use UIColor
#elseif canImport(AppKit)
// macOS – use NSColor
#else
// all other platforms – use a custom color object
#endif

Before canImport() was available we need to use #if os(macOS) instead, like this:

#if os(iOS) || os(tvOS) || os(watchOS)
// use UIColor
#else
// use NSColor
#endif

Using canImport() is an improvement because it lets you focus on what functionality you want rather than what operating system. So, if UIKit became available on macOS tomorrow you wouldn’t need to change your code to use it.

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