這是一個很有趣的問題，在Car2復制時候，CAR2的引擎復制了幾次？為什麼？

這個問題涉及到深淺復制，屬性的應用，以及內存的整理等多方面。結果很有趣，答案是三次。

#import 
#import "Car.h"

int main(int argc, const char * argv[])
{

    @autoreleasepool
    {
        Car *car = [[[Car alloc] init] autorelease];
        NSLog(@"%@", car);
        
        Car *car2 = [car copy];
        [car2 release];
    }
    return 0;
}

#import 
#import "Engine.h"
#import "Wheel.h"
@interface Car : NSObject

@property (nonatomic, retain) NSString* name;
@property (nonatomic, retain) NSString* brand;
@property (nonatomic, copy) Engine *myengine;
@property (nonatomic, copy) Wheel *mywheel;

@end

#import "Car.h"

@implementation Car


-(id)copyWithZone:(NSZone*) zone
{
//    深復制
    Car *car1 = [[[self class] allocWithZone:zone] init];
    car1.name = [[_name copy] autorelease];
    car1.brand = [[_brand copy] autorelease];
    car1.myengine = [[_myengine copy] autorelease];
    car1.mywheel = [[_mywheel copy] autorelease];
    return car1;
}

- (id)init
{
    if (self = [super init])
    {
        self.brand = @"奔馳";
        self.name = @"GLK300";
//        這些值賦予屬性的時候是通過copy的方式，故Wheel要通過alloc ->init -> copy 才能到達Car 的屬性
        self.mywheel = [[[Wheel alloc] init] autorelease];
        self.myengine = [[[Engine alloc] init] autorelease];
    }
    return self;
}

- (NSString*)description
{
    NSString* str = [NSString stringWithFormat:@"我是%@，我的名字是%@，我的引擎是%@，我的輪胎是%@", _brand , _name , _myengine , _mywheel];
    return str;
}

- (void)dealloc
{
//    屬性是指針變量，需要釋放
    [_mywheel release];
    [_myengine release];
//    在定義中retain 可以釋放
    [_name release];
    [_brand release];
    [super dealloc];
}
@end

#import 

@interface Engine : NSObject

@property (nonatomic,copy) NSString* brand;

@end

#import "Engine.h"

@implementation Engine

-(id)copyWithZone:(NSZone *)zone
{
//    淺復制
    Engine *eng = [[[self class] allocWithZone:zone] init];
    eng.brand = _brand;
    NSLog(@"%@馬達加上了！", _brand);
    return eng;
}

-(id)init
{
    self = [super init];
    self.brand = @"V12";
    return self;
}
-(NSString*)description
{
    return [NSString stringWithFormat:@"%@", _brand];
}

@end

#import 

@interface Wheel : NSObject

@property (nonatomic,copy) NSString* brand;

@end

#import "Wheel.h"

@implementation Wheel

-(id)copyWithZone:(NSZone *)zone
{
//    淺復制
    Wheel *wheel2 = [[[self class] allocWithZone:zone] init] ;
    wheel2.brand = _brand;
    NSLog(@"%@輪胎加好了！", _brand);
    return wheel2;
}

-(id)init
{
    self = [super init];
    self.brand = @"馬牌";
    return self;
}

-(NSString*)description
{
    return [NSString stringWithFormat:@"%@", _brand];
}

@end