---
title: Improving Objective-C API Declarations for Swift
framework: swift
role: article
role_heading: Article
path: swift/improving-objective-c-api-declarations-for-swift
---

# Improving Objective-C API Declarations for Swift

Use the NS_REFINED_FOR_SWIFT macro to change how an API is imported into Swift.

## Overview

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: @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: 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: @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: 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)     } }

## See Also

### Customizing Objective-C APIs

- [Designating Nullability in Objective-C APIs](swift/designating-nullability-in-objective-c-apis.md)
- [Renaming Objective-C APIs for Swift](swift/renaming-objective-c-apis-for-swift.md)
- [Grouping Related Objective-C Constants](swift/grouping-related-objective-c-constants.md)
- [Marking API Availability in Objective-C](swift/marking-api-availability-in-objective-c.md)
- [Making Objective-C APIs Unavailable in Swift](swift/making-objective-c-apis-unavailable-in-swift.md)