包含尖括号<>的奇数属性声明语法 [英] Odd property declaration syntax containing angular brackets <>

问题描述

我刚从2015 WWDC示例代码下载了FourInARow（ https://developer.apple.com/sample- code / wwdc / 2015 / ）并注意到文件中的奇怪属性声明 AAPLViewController.m

I just downloaded FourInARow from 2015 WWDC sample code (https://developer.apple.com/sample-code/wwdc/2015/) and noticed an odd property declaration in file AAPLViewController.m

@property NSArray<NSMutableArray<CAShapeLayer *> *> *chipLayers;

这是什么意思？

推荐答案

这是Objective-C的新增内容，名为 Lightweight Generics 。它是在iOS9 / OS X 10.11中引入的，目的是增强Swift和Objective-C之间的互操作性。正如文档所说：

It is a new addition to Objective-C, called Lightweight Generics. It was introduced in iOS9 / OS X 10.11 in order to enhance interoperability between Swift and Objective-C. As the documentation says:

使用轻量级通用参数化的NSArray，NSSet和NSDictionary类型
的Objective-C声明由Swift导入保存
有关其内容类型的信息。

Objective-C declarations of NSArray, NSSet and NSDictionary types using lightweight generic parameterization are imported by Swift with information about the type of their contents preserved.

例如，请考虑以下Objective-C属性声明：

For example, consider the following Objective-C property declarations:

@property NSArray<NSDate *>* dates; 
@property NSSet<NSString *>* words; 
@property NSDictionary<KeyType: NSURL *, NSData *>* cachedData;

以下是Swift进口的方法：

Here’s how Swift imports them:

var dates: [NSDate]
var words: Set<String> 
var cachedData: [NSURL: NSData]

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