# Improving Objective-C API Declarations for Swift Use the `NS_REFINED_FOR_SWIFT` macro to change how an API is imported into Swift. ## Overview If you want to expose an Objective-C API to Swift with a different declaration, but a similar underlying implementation, use the `NS_REFINED_FOR_SWIFT` macro. When you import an Objective-C API into Swift, you can adopt Swift-only types such as tuples. You can also reorder, combine, and rename parameters so the API matches other Swift APIs. ### Choose a New Name and Declaration The example below shows an Objective-C API that can be expressed more succinctly once it’s imported into Swift: ```occ @interface Color : NSObject - (void)getRed:(nullable CGFloat *)red green:(nullable CGFloat *)green blue:(nullable CGFloat *)blue alpha:(nullable CGFloat *)alpha; @end ``` Calling the `getRed(red:green:blue:alpha:)` method in Swift requires passing four in-out parameters. A reimagined Swift computed property that expresses the same functionality—getting the components of a color—can be written as a four-element tuple: ```swift var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) ``` The new name is shorter, but still understandable because it uses an industry-standard initialism for color components: RGBA. The property defined by the new declaration is easier to use in Swift. ### Expose the Existing Implementation Applying the `NS_REFINED_FOR_SWIFT` macro exposes the existing Objective-C API for reuse in your refined API. The existing API is renamed with double underscores (`__`) when it’s imported, to help prevent you from accidentally using the existing API elsewhere. The example below adds the `NS_REFINED_FOR_SWIFT` macro to the `getRed(red:green:blue:alpha:)` method: ```occ @interface Color : NSObject - (void)getRed:(nullable CGFloat *)red green:(nullable CGFloat *)green blue:(nullable CGFloat *)blue alpha:(nullable CGFloat *)alpha NS_REFINED_FOR_SWIFT; @end ``` The following rules determine how an API’s existing interface is imported: - Initializer methods are imported by Swift with double underscores (`__`) prepended to their first argument labels. - Object subscripting methods are imported by Swift as methods with double underscores (`__`) prepended to their base names, rather than as a Swift subscript, if either the getter or setter method is marked as `NS_REFINED_FOR_SWIFT`. - Other methods are imported with double underscores (`__`) prepended to their base names. ### Reuse the Existing Implementation You reuse an API by using its new name to call it in the implementation of a new API in Swift. The implementation of the new `rgba` property reuses the existing `__getRed(red:green:blue:alpha:)` method to ensure that functionality remains the same between Swift and Objective-C: ```swift extension Color { var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) { var r: CGFloat = 0.0 var g: CGFloat = 0.0 var b: CGFloat = 0.0 var a: CGFloat = 0.0 __getRed(red: &r, green: &g, blue: &b, alpha: &a) return (red: r, green: g, blue: b, alpha: a) } } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)