Swift 3.0 is exciting, but Objective-c also has small improvements--objective-c class properties

Because of the many exciting new features of Swift 3.0, it is easy to overlook minor changes in objective-c. Perhaps you would think that Apple's mention of objective-c is probably to improve and swift interoperability (translator note: The main point of interoperability is the OC code and the SWIFT code to convert each other), but Apple is still welcome developers to use OBJECTIVE-C to complete the work.

In this article, let's take a look at the newly added class properties in Objective-c.
Objective-c class Properties
Excerpt from the official version of Xcode 8:
Objective-c now supports class properties, which interoperate with Swift type properties.
They is declared as: @property (Class) NSString *somestringproperty;.
They is never synthesized. (23891898)
Translate as follows:

Objective-c now supports the class attribute, which corresponds to the Type property of Swift for the class attribute in OC.
They are stated as follows: @property (Class) NSString *somestringproperty;
Class properties are never automatically synthesized.
To practice, let's create a simple Objective-c class that contains several types. This is our ' User ' class interface, which looks like this:

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@interface User : NSObject@property (class, nonatomic, assign, readonly) NSInteger userCount;@property (class, nonatomic, copy) NSUUID *identifier;+ (void)resetIdentifier;@end

Here is a description of our two class properties, the first is a read-only integer type, and the second is a readable writable nsuuid type with the copy attribute. Be aware of classes that have attribute declarations.
Implementation is also very simple, we first need to store the ' identifier ' and ' UserCount ' class properties. Because they are class-level and not instance variables, we declare them static:

@implementation Userstatic NSUUID *_identifier = nil;static NSInteger _userCount = 0;

Now we have to create a ' getter ' and ' setter ' method for both attributes. As already mentioned in the release notes, these class attributes are never synthesized, so Xcode will report a warning if a ' getter ' or ' setter ' is missing. The first read-only ' UserCount ' requires only a getter method that returns the Count value. Note that using ' + ' turns our getter method into a class method:

+ (NSInteger)userCount {  return_userCount;}

The ' identifier ' property is required for both getter and setter methods. In the Getter method, if identifier is empty, we create a new identifier:

+ (NSUUID *)identifier {  if(_identifier == nil) {    _identifier = [[NSUUID alloc] init];  }  return_identifier;}+ (void)setIdentifier:(NSUUID *)newIdentifier {  if(newIdentifier != _identifier) {    _identifier = [newIdentifier copy];  }}

We have also created a basic initialization method for the ' User ' class that will update the Count property.

- (instancetype)init{  self = [superinit];  if(self) {    _userCount += 1;  }  returnself;}

The ' Resetidentifier ' class method is a convenient way to create a new identifier:

+ (void)resetIdentifier {  _identifier = [[NSUUID alloc] init];}@end

We can use point syntax after the class name to get to the class property:
User.usercount;
User.identifier;
Here is an example of the user class usage:

for(int i = 0; i < 3; i++) {    self.user = [[User alloc] init];    NSLog(@"User count: %ld",(long)User.userCount);    NSLog(@"Identifier = %@",User.identifier);}[User resetIdentifier];    NSLog(@"Identifier = %@",User.identifier);

Here is the output:

// User count: 1// Identifier = 4B98B7FD-F8DC-484A-92B2-B2BB20BCB709// User count: 2// Identifier = 4B98B7FD-F8DC-484A-92B2-B2BB20BCB709// User count: 3// Identifier = 4B98B7FD-F8DC-484A-92B2-B2BB20BCB709// Identifier = A0519681-1E08-4DF2-B2D1-D077CF2BDEFF

Note: Although this is a new feature of the LLVM compiler in Xcode 8, it still works for versions prior to iOS 10.
The generated Swift interface
It seems that the recent improvements in objective-c are just to improve interoperability with Swift. The newly added type attribute in objective-c corresponds to the use of class variables in Swift. Here's what we'll look like after we've converted the ' User ' class to Swift:

PUBLIC CLASS USER : NSOBJECT {   PUBLIC CLASS var USERCOUNT: INT { GET }  PUBLIC CLASS var IDENTIFIER: UUID!     public class func resetidentifier ()}

Note that the identifier Class property is an implicitly unpacked variable, meaning we never want it to be nil. To allow it to be nil, we need to add a ' nullable ' identifier to the OBJECTIVE-C attribute declaration. Our Swift variable will also be of an optional type. See [Using nullable to annotate objective-c] for more details.
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WWDC Session 405 What's New in LLVM

Swift 3.0 is exciting, but Objective-c also has small improvements--objective-c class properties