譯者序：
帶學生看Xcode API 文檔的時候，總有學生被通篇的英文搞暈，並詢問是否有中文版。
初步搜索和詢問的結果是，中文版有但是很少。（如果知道哪裡有，希望能夠分享一下這個信息）
於是決心從今天開始對Xcode API進行翻譯，這次的主題是Toll-Free Bridging。
Toll-Free Bridging
對象橋接
There are a number of data types in the Core Foundation framework and the Foundation framework that can be used interchangeably. This capability, called toll-free bridging, means that you can use the same data type as the parameter to a Core Foundation function call or as the receiver of an Objective-C message. For example,NSLocale (see NSLocale Class Reference) is interchangeable with its Core Foundation counterpart, CFLocale (see CFLocale Reference). Therefore, in a method where you see an NSLocale * parameter, you can pass aCFLocaleRef, and in a function where you see aCFLocaleRef parameter, you can pass anNSLocale instance. You cast one type to the other to suppress compiler warnings, as illustrated in the following example.
Core Foundation框架和Foundation框架中有大量的數據類型能被可交換的使用。這個能力被稱之為“對象橋接”，這就意味著你可以使用相同的數據類型作為Core Foudation函數調用的參數或者Objective-C消息的接受者。例如，NSLocale（參見NSLocale Class Reference）和它Core Foundation對應者CFLocale（參見 CFLocale Reference）是可交換的。因此，如果你在方法中看到了NSLocale *類型的參數，你就可以傳入一個NSLocale對象。你通過傳入一個類型到另一個去阻止編譯警告，代碼如下：
NSLocale *gbNSLocale = [[NSLocale alloc] initWithLocaleIdentifier:@en_GB];
CFLocaleRef gbCFLocale = (CFLocaleRef) gbNSLocale;
CFStringRef cfIdentifier = CFLocaleGetIdentifier (gbCFLocale);
NSLog(@cfIdentifier: %@, (NSString *)cfIdentifier);
// logs: cfIdentifier: en_GB
CFRelease((CFLocaleRef) gbNSLocale);
CFLocaleRef myCFLocale = CFLocaleCopyCurrent();
NSLocale * myNSLocale = (NSLocale *) myCFLocale;
[myNSLocale autorelease];
NSString *nsIdentifier = [myNSLocale localeIdentifier];
CFShow((CFStringRef) [@nsIdentifier: stringByAppendingString:nsIdentifier]);
// logs identifier for current locale
Note from the example that the memory management functions and methods are also interchangeable—you can useCFRelease with a Cocoa object andrelease andautorelease with a Core Foundation object.
值得注意的是，內存管理函數和方法也可交換的——你可以讓Cocoa對象去使用CFRelease函數並且讓Core Foundation對象去使用release和autorelease方法。
Note: When using garbage collection, there are important differences to how memory management works for Cocoa objects and Core Foundation objects. See “Using Core Foundation with Garbage Collection” for details.
注意：當使用垃圾回收機制時，Cocao對象和Core Foundation對象的內存管理有很大的不同。詳細請參見“Using Core Foundation with Garbage Collection”。
Toll-free bridging has been available since OS X v10.0. Table 13-1 provides a list of the data types that are interchangeable between Core Foundation and Foundation. For each pair, the table also lists the version of OS X in which toll-free bridging between them became available.
對象橋接從OS X v10.0版本開始可用。表格 13 - 1 提供了能在Core Fundation框架和Foundation框架之間交換使用的數據類型列表。對於每一對，表格也列出了 OS X中對象橋接可用的版本信息。
Table 13-1 Data types that can be used interchangeably between Core Foundation and Foundation
表格 13-1 能夠在Core Foundation框架和Foundation框架之間交換使用的數據對象
Core Foundation type Foundation class Availability
Core Foundation類型 Foundation類（基礎類） 可用版本
CFArrayRef NSArray OS X v10.0
CFAttributedStringRef NSAttributedString OS X v10.4
CFCalendarRef NSCalendar OS X v10.4
CFCharacterSetRef NSCharacterSet OS X v10.0
CFDataRef NSData OS X v10.0
CFDateRef NSDate OS X v10.0
CFDictionaryRef NSDictionary OS X v10.0
CFErrorRef NSError OS X v10.5
CFLocaleRef NSLocale OS X v10.4
CFMutableArrayRef NSMutableArray OS X v10.0
CFMutableAttributedStringRef NSMutableAttributedStringOS X v10.4
CFMutableCharacterSetRefNSMutableCharacterSet OS X v10.0
CFMutableDataRef NSMutableData OS X v10.0
CFMutableDictionaryRef NSMutableDictionary OS X v10.0
CFMutableSetRef NSMutableSet OS X v10.0
CFMutableStringRef NSMutableString OS X v10.0
CFNumberRef NSNumber OS X v10.0
CFReadStreamRef NSInputStream OS X v10.0
CFRunLoopTimerRef NSTimer OS X v10.0
CFSetRef NSSet OS X v10.0
CFStringRef NSString OS X v10.0
CFTimeZoneRef NSTimeZone OS X v10.0
CFURLRef NSURL OS X v10.0
CFWriteStreamRef NSOutputStream OS X v10.0
Note: Not all data types are toll-free bridged, even though their names might suggest that they are. For example,NSRunLoop is not toll-free bridged to CFRunLoop,NSBundle is not toll-free bridged to CFBundle, andNSDateFormatter is not toll-free bridged to CFDateFormatter.
注意：並不是所有的類型都是對象橋接，盡管其名稱讓它們看上去很像。例如，NSRunLoop和CFRunLoop不能對象橋接，NSBundle和CFBundle不能對象橋接，NSDateFormatter和CFDateFormatter不能對象橋接等。
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