比较Swift中C函数的指针

Question

我正在寻找一种方法来比较指向c函数的指针.例如:

let firstHandler = NSGetUncaughtExceptionHandler()

NSSetUncaughtExceptionHandler(onUncaughtException)
let secondHandler = NSGetUncaughtExceptionHandler()

if firstHandler == secondHandler {
    debugPrint("equal")
}

更新==,也没有===作品

目标CI可以表达如下:

NSUncaughtExceptionHandler *firstHandler = NSGetUncaughtExceptionHandler();

NSSetUncaughtExceptionHandler(onUncaughtException);
NSUncaughtExceptionHandler *secondHandler = NSGetUncaughtExceptionHandler();

if (firstHandler == secondHandler) {
    NSLog(@"equal");
}

提前致谢

Answer 1

通常,您无法在Swift中比较函数的相等性.但是,NSSetUncaughtExceptionHandler返回一个

(@convention(c) (NSException) -> Swift.Void)?

即一个(可选的)C兼容函数,这样的函数可以强制转换为(可选)原始指针,具有 unsafeBitCast:

let ptr1 = unsafeBitCast(firstHandler, to: Optional<UnsafeRawPointer>.self) 
let ptr2 = unsafeBitCast(secondHandler, to: Optional<UnsafeRawPointer>.self) 

然后可以比较平等

if ptr1 == ptr2 { .. }

一个自包含的例子:

func exceptionHandler1(exception : NSException) { }

func exceptionHandler2(exception : NSException) { }

NSSetUncaughtExceptionHandler(exceptionHandler1)
let firstHandler = NSGetUncaughtExceptionHandler()
NSSetUncaughtExceptionHandler(exceptionHandler2)
let secondHandler = NSGetUncaughtExceptionHandler()

let ptr1 = unsafeBitCast(firstHandler, to: Optional<UnsafeRawPointer>.self) 
let ptr2 = unsafeBitCast(secondHandler, to: Optional<UnsafeRawPointer>.self) 

print(ptr1 == ptr2) // false