Copy property on Objective-C

Copy property on Objective-C.md

Testing Copy property on Objective-C

AppDelegate.m

#import "AppDelegate.h"
#import "Model.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    Model *model = [Model new];
    [model go];
    
    return YES;
}

Model.h

#import <Foundation/Foundation.h>
#import "Sub.h"

@interface Model : NSObject

@property (nonatomic, readwrite, copy) Sub *sub;
@property (nonatomic, readwrite, copy) NSString *str;
@property (nonatomic, readwrite, copy) NSMutableString *mutableStr;

- (void)go;
@end

Model.m

#import "Model.h"

@implementation Model

- (instancetype)init {
    self = [super init];
    if (self) {
        _sub = [Sub new];
        _str = @"hello";
        _mutableStr = [[NSMutableString alloc] initWithString:@"hello"];
    }
    return self;
}

- (void)go {
    Sub *sub = [Sub new];
    NSLog(@"sub1: %p", self.sub);  // sub1: 0x7fda30527250
    NSLog(@"sub2: %p", sub);       // sub2: 0x7fda30527290
    self.sub = sub;
    NSLog(@"sub3: %p", self.sub);  // sub3: 0x7fda30615e00
    self.sub = self.sub;
    NSLog(@"sub4: %p", self.sub);  // sub4: 0x7fda307a0010
    
    NSString *str = @"world";
    
    NSLog(@"str1: %p", self.str);  // str1: 0x1083fe080
    NSLog(@"str2: %p", str);       // str2: 0x1083fe120
    self.str = str;
    NSLog(@"str3: %p", self.str);  // str3: 0x1083fe120
    self.str = self.str;
    NSLog(@"str4: %p", self.str);  // str4: 0x1083fe120
    
    NSMutableString *mutableStr = [[NSMutableString alloc] initWithString:@"hello"];
    

    NSLog(@"mutableStr1: %p", self.mutableStr);  // mutableStr1: 0x7fbb430085c0
    NSLog(@"mutableStr2: %p", mutableStr);       // mutableStr2: 0x7fbb41520350
    self.mutableStr = mutableStr;
    NSLog(@"mutableStr3: %p", self.mutableStr);  // mutableStr3: 0xa00006f6c6c65685
    self.mutableStr = self.mutableStr;
    NSLog(@"mutableStr4: %p", self.mutableStr);  // mutableStr4: 0xa00006f6c6c65685
    self.mutableStr = mutableStr;
    NSLog(@"mutableStr5: %p", mutableStr);       // mutableStr5: 0x7fbb41520350
    NSLog(@"mutableStr6: %p", self.mutableStr);  // mutableStr6: 0xa00006f6c6c65685
    [mutableStr appendString:@" world"];
    NSLog(@"mutableStr7: %@", self.mutableStr);  // mutableStr7: hello
    NSLog(@"mutableStr8: %@", mutableStr);       // mutableStr8: hello world
    self.mutableStr = mutableStr;
    NSLog(@"mutableStr9: %p", self.mutableStr);  // mutableStr9: 0x7fbb417a2f90
}

@end

Sub.h

#import <Foundation/Foundation.h>

@interface Sub : NSObject <NSCopying>

@end

Sub.m

#import "Sub.h"

@implementation Sub

- (instancetype)copyWithZone:(NSZone *)zone {
    Sub *copy = [[[self class] allocWithZone:zone] init];
    return copy;
}

@end