objective-c - 在某些情况下禁用自动桥接

Question

来自 Using Swift with Cocoa and Objective-C - Working with Cocoa Frameworks :

Swift automatically converts some Objective-C types to Swift types, and some Swift types to Objective-C types.

但在某些情况下，自动桥接是不可取的，例如性能问题或桥接实现中的错误。

如何在特定情况下禁用此行为？例如。用于特定语句或特定类。

Answer 1

我希望有一个 NS_DO_NOT_BRIDGE_FOR_SWIFT 宏，但遗憾的是，它不存在。浏览 Swift 的源代码，我无法找到禁用桥接的神奇宏。下面的回答很啰嗦。它依赖于 2 个事实:

1. 核心基础类型(即 CF*)未桥接到 Swift 中
2. Core Foundation (CF*) 和 Cocoa (NS*) 类型之间有免费桥接

让我们看一个例子。首先，Objective-C 方面:

// MyClass.h
@interface MyClass : NSObject

NS_ASSUME_NONNULL_BEGIN
- (NSArray *)  randomNumbers NS_SWIFT_UNAVAILABLE("");  // mark this method as unavailable in Swift
- (CFArrayRef) cfRandomNumbers NS_REFINED_FOR_SWIFT;    // tell the compiler that you have a refined version for Swift
NS_ASSUME_NONNULL_END

@end

// MyClass.m
#import "MyClass.h"

@implementation MyClass

- (NSArray *) randomNumbers {
    return @[ @1, @2, @3 ];
}

- (CFArrayRef) cfRandomNumbers {
    return CFBridgingRetain([self randomNumbers]);  // toll-free
}

@end

swift 方面

extension MyClass {
    // Even though we marked `randomNumbers` as unavailable in Swift, we can't
    // use the same signature. Must name it something else.
    func objcRandomNumbers() -> NSArray {
        // Methods marked with NS_REFINED_FOR_SWIFT pick up
        // double-underscore prefix in their names
        return __cfRandomNumbers().takeUnretainedValue() as NSArray
    }
}

let obj = MyClass()
let arr = obj.objcRandomNumbers() // no bridging here

好处是一切都被记录下来，因此是“官方的”。您可以通过 Profiler 运行代码来检查是否发生了桥接。