译者序：
带学生看Xcode API 文档的时候，总有学生被通篇的英文搞晕，并询问是否有中文版。
初步搜索和询问的结果是，中文版有但是很少。（如果知道哪里有，希望能够分享一下这个信息）
于是决心从今天开始对Xcode API进行翻译，这次的主题是"Toll-Free Bridging"。
英文原版版权归苹果公司所有，翻译内容仅供学习参考。
首发网址：http://blog.csdn.net/duzixi/article/details/38325021
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Toll-Free Bridging
对象桥接
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框架中有大量的数据类型能被可交换的使用。这个能力被称之为“对象桥接”，这就意味着你可以使用相同的数据类型作为Core Foudation函数调用的参数或者Objective-C消息的接受者。例如，NSLocale（参见NSLocale Class Reference）和它Core Foundation对应者CFLocale（参见 CFLocale Reference）是可交换的。因此，如果你在方法中看到了NSLocale
*类型的参数，你就可以传入一个NSLocale对象。你通过传入一个类型到另一个去阻止编译警告，代码如下：
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，内存管理函数和方法也可交换的——你可以让Cocoa对象去使用CFRelease函数并且让Core Foundation对象去使用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：当使用垃圾回收机制时，Cocao对象和Core Foundation对象的内存管理有很大的不同。详细请参见“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.
对象桥接从OS X v10.0版本开始可用。表格 13 - 1 提供了能在Core Fundation框架和Foundation框架之间交换使用的数据类型列表。对于每一对，表格也列出了 OS X中对象桥接可用的版本信息。
Table 13-1 Data types that can be used interchangeably between Core Foundation and Foundation
表格 13-1 能够在Core Foundation框架和Foundation框架之间交换使用的数据对象
Core Foundation type Foundation class Availability
Core Foundation类型 Foundation类（基础类） 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：并不是所有的类型都是对象桥接，尽管其名称让它们看上去很像。例如，NSRunLoop和CFRunLoop不能对象桥接，NSBundle和CFBundle不能对象桥接，NSDateFormatter和CFDateFormatter不能对象桥接等。
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