在什么情况下，Objective-c中的@synthesize是自动的? [英] Under what conditions is @synthesize automatic in Objective-c?

问题描述

在什么情况下，Objective-c中的@synthesize自动生成?

也许在使用LLVM 3.0及更高版本时?从网络上看，从Xcode 4开始似乎不需要@synthesize.但是，我使用Xcode 4并在没有@synthesize属性时收到警告.

Perhaps when using LLVM 3.0 and up? From reading around the net it seems like @synthesize is unnecessary starting with Xcode 4. However I'm using Xcode 4 and receiving warnings when I don't @synthesize a property.

对为什么不自动合成属性的一些回应似乎暗示@synthesize在某些情况下可以在某些时候省略.

Some of the responses to Why don't properties get automatically synthesized seem to imply @synthesize can be omitted at some point under some circumstances.

另一(旧)参考提示@synthesize在将来的某个时候可能会自动出现.

Another (old) reference hinting that @synthesize might be automatic at some point in the future.

推荐答案

从clang 3.2(大约在2012年2月)开始，默认情况下提供了Objective-C属性的默认综合"(或自动属性综合").基本上就像您最初阅读的博客文章所述: http: //www.mcubedsw.com/blog/index.php/site/comments/new_objective-c_features/(除了该帖子将功能描述为启用，然后禁用"；我不知道这是否是Xcode的问题，或者clang开发人员本身是否来回讨论此问题.

As of clang 3.2 (circa February 2012), "default synthesis" (or "auto property synthesis") of Objective-C properties is provided by default. It's essentially as described in the blog post you originally read: http://www.mcubedsw.com/blog/index.php/site/comments/new_objective-c_features/ (except that that post describes the feature as "enabled, then disabled"; I don't know if that's an issue with Xcode or if the clang developers themselves have gone back and forth on the question).

据我所知，在clang 3.2中默认不合成属性的唯一情况是这些属性是从协议继承的.这是一个示例:

As far as I know, the only case in which properties will not be default-synthesized in clang 3.2 is when those properties have been inherited from a protocol. Here's an example:

#import <Foundation/Foundation.h>

@protocol P
@property int finicky;
@end

@interface A : NSObject <P>
@property int easygoing;
@end

@implementation A
@end

int main() { A *a = [A new]; a.easygoing = 0; a.finicky = 1; }

如果您编译此示例，则会收到警告:

If you compile this example, you'll get a warning:

test.m:11:17: warning: auto property synthesis will not synthesize property
      declared in a protocol [-Wobjc-protocol-property-synthesis]
@implementation A
                ^
test.m:4:15: note: property declared here
@property int finicky;
              ^
1 warning generated.

如果您运行它，则会在运行时收到错误消息:

and if you run it, you'll get an error from the runtime:

objc[45820]: A: Does not recognize selector forward:: (while forwarding setFinicky:)
Illegal instruction: 4

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