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Without annotations, Swift imports every Objective-C pointer as an implicitly unwrapped optional. That hides crashes and produces ugly Swift APIs.

Objective-C offers three nullability keywords:

• nonnull imports as a plain type
• nullable imports as an optional
• null_unspecified imports as implicitly unwrapped

Add nullability directly to a method signature so Swift sees the intent.

Wrap a header section in audited macros so everything defaults to nonnull; you then only mark the exceptions with nullable.

Annotate collections with lightweight generics so Swift imports typed arrays instead of [Any].

With annotations, the bridge produces clean Swift signatures. The nullable return becomes a real optional you can safely unwrap.

NSInteger maps to Int, BOOL to Bool, and NSString * to String. Knowing these mappings prevents accidental bridging classes like NSNumber in Swift.

Use NS_ENUM and NS_OPTIONS so Swift imports proper enums and option sets instead of bare integers.

Use NS_SWIFT_NAME to give a method a more idiomatic Swift name without changing the Objective-C name.

Methods with a trailing NSError ** parameter import as Swift throwing functions, so callers can use try.

Leaving any pointer unannotated reintroduces unsafe implicit optionals. Audit every public header so the entire Swift-facing surface is precise.

Test your bridge type-mapping knowledge.

You learned nullability annotations, audited regions, lightweight generics, NS_ENUM, NS_SWIFT_NAME, and error bridging to expose clean, safe Swift APIs from Objective-C.