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Comment by _0w8t | Hacker News Reader

A friend of mine have been working with porting to iPhone some Android and web apps. I recently asked his opinion of Swift. He said he had no idea as the essential libraries the apps use are in C or Objective-C, so there were no choice but to use Objective-C for the apps. This was surprising, as I thought that calling Objective-C from Swift should be transparent. But it turned out it was not as many small but important details make the whole thing rather messy. So I also wandered what exactly Apple wanted to get with Swift if it lacks even in Objective-C interoperability.

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I'm not sure where your friend was getting that information, or what small details he was referring to. Calling Objective-C from within Swift is remarkably transparent -- where you might have called `[foo bar:baz];`, you call `foo.bar(baz)`.

In some cases, wordy Objective-C names will get mapped to Swift's tidier conventions, but the public APIs are all documented in both languages, and Xcode's auto-complete is pretty good at helping you figure it out.

The issue was with exceptions.

Swift was designed to have very good Objective-C and C compatibility, using the clang compiler to understand headers and generate any Swift binding/bridge at compile time. It will punt on trying to support some things, such as inline functions which are declared as C macros, but generally will try to expose everything.

Typically a maintained Objective-C library will evaluate their ability to be used from Swift, and use attributes/macros where necessary to tweak the code import to generate a higher quality Swift interface. Examples would be declaring that a method never returns a nil value, or creating a clearer function name, or switching to the newer Objective-C enum/set styles to have the enumerations generated as Swift types rather than having their API take a raw integer constant or string.

AFAIK, all of apple's frameworks are C or Objective C interfaces, and the swift interface is nearly all generated based on the code and public annotations.

Objective C from Swift is trivial, don’t rely on that friend for technical advice.

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