How does the Finder know the right app to open a file with? Or QuickLook how to preview its contents? Or other services like Spotlight know how to index and handle files? UTIs.
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Last of 3 articles explains how macOS selects and starts the app with which to open a document which you double-clicked/tapped.
Second of 3 articles explains how macOS puts documents through its security checks before opening them.
How does macOS open the document that you double-click/tap? First of 3 parts explaining what should happen and where it can go wrong.
Additional information is now shown for UTIs, it has its own custom app icon, and works wonderfully in Dark Mode.
What to do when you need to use Uniform Type Identifiers, only to discover that Apple’s reference manual hasn’t been updated for nearly 9 years: write an app!
When to use as, as!, or as?, how to handle Any, and when you need to use var instead of let even though you don’t change the value.
A crashing app points out the problems of using functions that return values of ‘Any’ type. Here’s one solution.
Akihabara is fertile territory for the likes of emoji: exploratory, fun, chic, mobile, language-free, but deeply flawed.
The Eclectic Light Company 