在macOS上使用Swift制作从打印机ID到打印机名称的映射

Question

我正在尝试使用MacOS上的Swift制作从打印机ID到打印机名称的地图。

Objective-C版本如下。这很有效。

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        CFArrayRef printerList;
        PMServerCreatePrinterList(kPMServerLocal, &printerList);
        NSMutableDictionary<NSString*,NSString*> *result = [NSMutableDictionary<NSString*,NSString*> dictionary];

        if (printerList) {
            CFIndex numberOfPrinters = CFArrayGetCount(printerList);
            for (CFIndex printerIndex = 0; printerIndex < numberOfPrinters; printerIndex++) {
                PMPrinter printer = (PMPrinter)CFArrayGetValueAtIndex(printerList, printerIndex);
                CFStringRef printerID = PMPrinterGetID(printer);
                CFStringRef printerName = PMPrinterGetName(printer);
                result[(__bridge NSString*)printerID] = (__bridge NSString*)printerName;
            }
            NSLog(@"Result1 = %@", result.description);
        }

        CFRelease(printerList);

        NSLog(@"Result2 = %@", result.description);
    }

    return 0;
}

另一方面，以下Swift版本与EXC_BAD_ACCESS崩溃。

import Foundation

var printerList : Unmanaged<CFArray>?
let kPMServerLocal = unsafeBitCast(0, to: PMServer.self) // #define kPMServerLocal ((PMServer)NULL)
PMServerCreatePrinterList(kPMServerLocal, &printerList)

var result : [String : String] = [:]

if let list = printerList {
    let retainedList = list.takeRetainedValue()
    let numberOfPrinters = CFArrayGetCount(retainedList)
    for printerIndex in 0..<numberOfPrinters {
        let printer = CFArrayGetValueAtIndex(retainedList, printerIndex)
        let printerID = PMPrinterGetID(OpaquePointer(printer)!)!.takeRetainedValue() as String
        let printerName = PMPrinterGetName(OpaquePointer(printer)!)!.takeRetainedValue() as String
        result[printerID] = printerName
    }
    print("Result1 = " + result.description) // Successful
}

print("Result2 = " + result.description) // EXC_BAD_ACCESS

我猜内存管理不合适。如何修改代码？