/*
 extern都是写在.h文件中，声明全局变量或常量；这里仅仅是声明，实现是在.m文件中
 如果这里只声明，而在.m文件中没有实现，外部如果使用的话编译会报错
 */
extern NSString *name1;         //声明全局变量-外部可以修改
extern NSString *const name2;   //声明全局常量-外部不能修改

@interface Person : NSObject
    //显式声明extern表明其不是成员变量，而是全局变量
    extern NSString *name;
    extern int age;
@end

#import "Person.h"
/*
 extern声明全局变量或常量的实现，必须实现，否则外部使用时，编译期会报错
 */
NSString *name1 = @"zhangsan";
NSString *const name2 = @"lisi";

@implementation Person
    NSString *name = "zhangsan";
    age = 18;
@end

#import "WGMainObjcVC.h"
@implementation WGMainObjcVC
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"修改前--全局变量name1:%@",name1);  //
    name1 = @"zhangsan11111";
    NSLog(@"修改后--全局变量name1:%@",name1);
    NSLog(@"修改前--全局常量name2:%@",name2);
    //name2 = @"lisi"; 编译器会报错:Cannot assign to variable 'name2' with const-qualified   
    type 'NSString *const  _Nonnull __strong'
}
@end

打印结果: 修改前--全局变量name1:zhangsan
        修改后--全局变量name1:zhangsan11111
        修改前--全局常量name2:lisi

@implementation WGMainObjcVC
- (void)viewDidLoad {
    [super viewDidLoad];
    //只是用来获取全局变量(包括全局静态变量)的值，不能用于定义变量
    extern NSString *name1;
    NSLog(@"获取到的全局变量值是:%@",name1);
}
@end

    @interface WGMainObjcVC : UIViewController
    @property(nonatomic, copy) NSString *name;
    @end
    
    @implementation WGMainObjcVC
    @dynamic name;   
    - (void)viewDidLoad {
        [super viewDidLoad];
        self.view.backgroundColor = [UIColor whiteColor];
        self.name = @"zhangsan";
    }
    @end

    @interface WGMainObjcVC : UIViewController
    @property(nonatomic, copy) NSString *name;
    @end

    @implementation WGMainObjcVC
    //这句代码也可以不写，默认生成成员变量的名称是_name
    @synthesize name = AAA;  
    - (void)viewDidLoad {
        [super viewDidLoad];
        self.view.backgroundColor = [UIColor whiteColor];
        self.name = @"zhangsan";
    }
    @end

    @interface WGMainObjcVC()
    @property(nonatomic, assign) int totalTicket;  //总票数
    @end
    @implementation WGMainObjcVC
    - (void)viewDidLoad {
        [super viewDidLoad];
        _totalTicket = 10;
        //线程1 卖5张
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            for (int i = 0; i < 5; i++) {
                [self sealTicket];
            }
        });
        //线程1 卖5张
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            for (int i = 0; i < 5; i++) {
                [self sealTicket];
            }
        });
    }

    -(void)sealTicket {
        _totalTicket -= 1;
        NSLog(@"当前剩余票数:%d",_totalTicket);
    }
    @end
    打印结果: 当前剩余票数:8
            当前剩余票数:9
            当前剩余票数:7
            当前剩余票数:7
            当前剩余票数:6
            当前剩余票数:5
            当前剩余票数:4
            当前剩余票数:3
            当前剩余票数:2
            当前剩余票数:1

    -(void)sealTicket {
        @synchronized (self) { //会对传入的对象分配一个递归锁
            _totalTicket -= 1;
            NSLog(@"当前剩余票数:%d",_totalTicket);
        }
    }

    var score = 70                          var score = 70
    switch score {                          switch score {
    case 0...60:                            case 0...60:
        print("成绩不及格")                       print("成绩不及格")
    case 61...70:                           case 61...70:
        print("成绩良好")                         print("成绩良好")
    default:                                     fallthrough
        print("成绩优秀")                     case 31...60: 
    }                                            print("成绩不及格")
                                                 fallthrough
                                            default:
                                                print("成绩优秀") 
                                            }                    

    打印结果: 成绩良好                         打印结果: 成绩良好
                                                    成绩不及格
                                                    成绩优秀

typealias Location = CGPoint

protocol WGOneProtocol : class {
    //设置关联类型
    associatedtype GenderType
    var sex: GenderType {get}  //性别
}

class Student : WGOneProtocol{
    //实现协议中的属性 必须通过typealias指定类型
    typealias GenderType = Bool
    var sex: GenderType = false 
}

class Animal : WGOneProtocol {
    //实现协议中的属性 必须通过typealias指定类型
    typealias GenderType = Int
    var sex: GenderType = 0
}

    struct MyStruct {
        var name = ""
        var age = 0
        mutating func testFunc() {
            age = 18
        }
    }
    public override func viewDidLoad() {
        super.viewDidLoad()

        //这里必须是var修饰，否则编译器会报错
        var a = MyStruct()
        a.testFunc()
        NSLog("age:\(a.age)")
    }
    打印结果: age:18

    class WGMyClass {
        final var name = ""
        final func testFunc(){
            NSLog("WGMyClass->testFunc")
        }
    }

public override func viewDidLoad() {
    super.viewDidLoad()
    NSLog("1111")
    defer {
        NSLog("------")
    }
    NSLog("2222")
}

打印结果: 1111
         2222
         ------

    public override func viewDidLoad() {
        super.viewDidLoad()
        NSLog("1111")
        defer {
            NSLog("2222------")
        }
        defer {
            NSLog("3333------")
        }
        defer {
            NSLog("4444------")
        }
        NSLog("5555")
    }
    打印结果: 1111
            5555
            4444------
            3333------
            2222------

MRC手动管理（7个）: assign/retain/copy/readwrite/readonly/nonatomic/atomic  
ARC自定管理（8个）: assign/strong/copy/readwrite/readonly/nonatomic/atomic/weak

直接进行赋值操作
-(void)setAge:(NSInteger)age {
    _age = age;
}

@interface WGMainObjcVC()
@property(nonatomic, assign) Person *p1;
@end

@implementation WGMainObjcVC
- (void)viewDidLoad {
    [super viewDidLoad];
    self.p1 = nil;
    {
        Person *p0 = [[Person alloc]init];
        //p1是用assign修饰的，所以既不持有对象的强引用也不持有对象的弱引用
        self.p1 = p0;
        NSLog(@"p1的地址是：%@---p0的地址是:%@",self.p1, p0);
    }
    NSLog(@"p1的地址是：%@",self.p1);
}
@end
    
打印结果: p1的地址是：<Person: 0x600003438430>---p0的地址是:<Person: 0x600003438430>
        编辑可以通过，但是在运行的时候会报错，报错信息如下
        message sent to deallocated instance 0x600003438430

Runtime源代码 
id objc_getProperty(id self, SEL _cmd, ptrdiff_t offset, BOOL atomic) {
    if (offset == 0) {
        return object_getClass(self);
    }

    // Retain release world
    id *slot = (id*) ((char*)self + offset);
    if (!atomic) return *slot;

    // Atomic retain release world
    spinlock_t& slotlock = PropertyLocks[slot];
    slotlock.lock();   //加锁
    id value = objc_retain(*slot);
    slotlock.unlock();  //解锁
    
    //for performance, we (safely) issue the autorelease OUTSIDE of the spinlock.
    return objc_autoreleaseReturnValue(value);
}

using spinlock_t = mutex_tt<LOCKDEBUG>;
class mutex_tt : nocopy_t {
    os_unfair_lock mLock;  //这是iOS10之后用到的互斥锁
}

setter方法释放旧对象，retain新对象
-(void)setName:(NSString *)name {
    if (_name != name) {
        [_name release];
        _name = [name retain];
    }
}

@interface Person : NSObject
@property(nonatomic, strong) NSString *name;
@end

//@dynamic 告诉编辑器不自动生成name属性的getter和setter方法实现和对应的成员变量
@implementation Person
@dynamic name;   
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    Person *p = [[Person alloc]init];
    //程序编译期不会报错，但在运行时会报错：因为@dynamic的声明，系统没有生成对应的setter/getter方法
    //reason: '-[Person setName:]: unrecognized selector sent to instance 0x600001d6a9a0'
    p.name = @"zhangsan";
}

weak修饰基本数据类型时，编译器会报错，weak只能用于对象类型
@property(nonatomic, weak) NSInteger age;
Property with 'weak' attribute must be of object type

/**
 * The global weak references table. Stores object ids as keys,
 * and weak_entry_t structs as their values.
 */

struct weak_table_t {
    weak_entry_t *weak_entries;       //保存了所有指向指定对象的weak指针
    size_t    num_entries;            //weak对象的存储空间
    uintptr_t mask;                   //参与判断引用计数辅助量
    uintptr_t max_hash_displacement;  //hash key 最大偏移值
};

//weak全局表中存储weak定义的对象的表结构weak_entry_t,它负责维护和存储指向一个对象的所有弱引用hash表
struct weak_entry_t {
    //是对泛型对象的指针做了一个封装,通过这个泛型类来解决内存泄漏的问题
    DisguisedPtr<objc_object> referent; 
    union {
        struct {
            weak_referrer_t *referrers;
            uintptr_t        out_of_line_ness : 2;
        uintptr_t        num_refs : PTR_MINUS_2;
        uintptr_t        mask;
        uintptr_t        max_hash_displacement;
    };
    struct {
        // out_of_line_ness field is low bits of inline_referrers[1]
        weak_referrer_t  inline_referrers[WEAK_INLINE_COUNT];
    };
};
...
}

源对象类型        拷贝方法         副本对象类型      是否产生新对象      拷贝类型
NSString         copy           NSString           NO         浅拷贝(指针拷贝)
                 mutableCopy    NSMutableString    YES        深拷贝(内容拷贝)
                                 
NSMutableString  copy           NSString           YES        深拷贝(内容拷贝)
                 mutableCopy    NSMutableString    YES        深拷贝(内容拷贝)
                                 
NSArray          copy           NSArray             NO        浅拷贝(指针拷贝)
                 mutableCopy    NSMutableArray      YES       深拷贝(内容拷贝)
                                 
NSMutableArray   copy           NSArray             YES       深拷贝(内容拷贝)
                 mutableCopy    NSMutableArray      YES       深拷贝(内容拷贝)
                                 
NSXXXX           copy           NSXXXX              NO        浅拷贝(指针拷贝)
                 mutableCopy    NSMutableArray      YES       深拷贝(内容拷贝)
                                  
NSMutableXXXX    copy           NSXXXX              YES       深拷贝(内容拷贝)                         
                 mutableCopy    NSMutableXXXX       YES       深拷贝(内容拷贝)

 array1    浅拷贝    array2      array1   深拷贝    array2   深拷贝        
   0------->A<--------0           0------->A        0------->A
   1------->B<--------1           1------->B        1------->B
   2------->C<--------2           2------->C        2------->C
   3------->D<--------3           3------->D        3------->D

//.m文件
@interface WGMainObjcVC()
@property(nonatomic, strong) NSString *strongStr;
@property(nonatomic, copy) NSString *copyyStr;
@end

@implementation WGMainObjcVC
- (void)viewDidLoad {
    [super viewDidLoad];
    //1. 用不可变字符串赋值操作, 无论strong或者copy，其指向的地址都是baseStr的地址，即copy拷贝的是对象的地址
    NSString *baseStr = [NSString stringWithFormat:@"123"];
    _strongStr = baseStr;
    _copyyStr = baseStr;
    NSLog(@"baseStr对象地址: %p,对象的指针地址:%p, 值:%@",baseStr,&baseStr,baseStr);
    NSLog(@"strongStr对象地址: %p,对象的指针地址:%p, 值:%@",_strongStr,&_strongStr,_strongStr);
    NSLog(@"copyyStr对象地址: %p,对象的指针地址:%p, 值:%@",_copyyStr,&_copyyStr,_copyyStr);
}
@end
    
打印结果: baseStr对象地址: 0x8c43b6f85e3255c4,对象的指针地址:0x7ffee68ae790, 值:123
        strongStr对象地址: 0x8c43b6f85e3255c4,对象的指针地址:0x7f9726c08790, 值:123
        copyyStr对象地址: 0x8c43b6f85e3255c4,对象的指针地址:0x7f9726c08798, 值:123

//1. 用不可变字符串赋值操作, 无论strong或者copy，其指向的地址都是baseStr的地址，即copy拷贝的是对象的地址
NSString *baseStr = [NSString stringWithFormat:@"123"];
NSLog(@"baseStr对象地址: %p,对象的指针地址:%p, 值:%@",baseStr,&baseStr,baseStr);
_strongStr = baseStr;
_copyyStr = baseStr;
//当重新对baseStr进行赋值时，因为baseStr是不可变字符串，为了保持不可变性，系统会另外开辟内存空间来存放变更后的内容
//但是这并不会影响copy和strong修饰的对象
baseStr = @"456";
NSLog(@"baseStr对象地址: %p,对象的指针地址:%p, 值:%@",baseStr,&baseStr,baseStr);
NSLog(@"strongStr对象地址: %p,对象的指针地址:%p, 值:%@",_strongStr,&_strongStr,_strongStr);
NSLog(@"copyyStr对象地址: %p,对象的指针地址:%p, 值:%@",_copyyStr,&_copyyStr,_copyyStr);

打印结果: baseStr对象地址: 0xf113747087f4ecf8,对象的指针地址:0x7ffee2874790, 值:123
        baseStr对象地址: 0x10d390610,对象的指针地址:0x7ffee2874790, 值:456
        strongStr对象地址: 0xf113747087f4ecf8,对象的指针地址:0x7f8391a0e980, 值:123
        copyyStr对象地址: 0xf113747087f4ecf8,对象的指针地址:0x7f8391a0e988, 值:123

Person *p1 = [[Person alloc]init];
Person *p2 = [[Person alloc]init];
Person *p3 = [[Person alloc]init];

NSArray *baseArr = @[p1, p2, p3];
NSArray *copyArr = [baseArr copy];
NSMutableArray *mutableCopyArr = [baseArr mutableCopy];

NSLog(@"\n源数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",baseArr,baseArr[0],baseArr[1],baseArr[2]);
NSLog(@"\n浅拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",copyArr,copyArr[0],copyArr[1],copyArr[2]);
NSLog(@"\n深拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",mutableCopyArr,mutableCopyArr[0],mutableCopyArr[1],mutableCopyArr[2]);
    
打印结果: 源数组地址:0x600000045eb0
            ---元素1:0x60000001ecf0
            ---元素2:0x60000001ed20
            ---元素3:0x60000001ed40
        浅拷贝copy后数组地址:0x600000045eb0
            ---元素1:0x60000001ecf0
            ---元素2:0x60000001ed20
            ---元素3:0x60000001ed40
        深拷贝copy后数组地址:0x600000046000
            ---元素1:0x60000001ecf0
            ---元素2:0x60000001ed20
            ---元素3:0x60000001ed40

@interface Person : NSObject
@property(nonatomic, strong) NSString *name;
@end

@interface Person()<NSCopying>
@end


@implementation Person
-(id)copyWithZone:(NSZone *)zone {
    Person *p = [[self class] allocWithZone:zone];
    p.name = [_name copy];
    return p;
}
@end

Person *p1 = [[Person alloc]init];
Person *p2 = [[Person alloc]init];
Person *p3 = [[Person alloc]init];

NSArray *baseArr = @[p1, p2, p3];
NSArray *copyArr = [baseArr copy];
NSMutableArray *mutableCopyArr = [[NSMutableArray alloc]initWithArray:baseArr copyItems:YES];

NSLog(@"\n源数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
baseArr,baseArr[0],baseArr[1],baseArr[2]);
NSLog(@"\n浅拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
copyArr,copyArr[0],copyArr[1],copyArr[2]);
NSLog(@"\n深拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
mutableCopyArr,mutableCopyArr[0],mutableCopyArr[1],mutableCopyArr[2]);

打印结果: 源数组地址:0x610000055ea0
            ---元素1:0x610000006180
            ---元素2:0x610000006190
            ---元素3:0x6100000061a0
        浅拷贝copy后数组地址:0x610000055ea0
            ---元素1:0x610000006180
            ---元素2:0x610000006190
            ---元素3:0x6100000061a0
        深拷贝copy后数组地址:0x610000055ff0
            ---元素1:0x6100000061b0
            ---元素2:0x6100000061c0
            ---元素3:0x6100000061d0

    @interface Person : NSObject
    @property(nonatomic, strong) NSString *name;
    @property(nonatomic, strong) NSArray *studentArr;
    @end

@interface Person : NSObject
@property(nonatomic, strong) NSString *name;
@end

@interface Person()<NSCoding>
@end

@implementation Person
-(instancetype)initWithCoder:(NSCoder *)coder {
    self = [super init];
    if (self) {
        self.name = [coder decodeObjectForKey:@"name"];
    }
    return self;
}
-(void)encodeWithCoder:(NSCoder *)coder {
    [coder encodeObject:self.name forKey:@"name"];
}
@end
    
Person *p1 = [[Person alloc]init];
Person *p2 = [[Person alloc]init];
Person *p3 = [[Person alloc]init];
NSArray *baseArr = @[p1, p2, p3];
NSArray *copyArr = [baseArr copy];

//2、归档和解档
//归档
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:baseArr];
//接档
NSMutableArray *mutableCopyArr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

NSLog(@"\n源数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
baseArr,baseArr[0],baseArr[1],baseArr[2]);
NSLog(@"\n浅拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
copyArr,copyArr[0],copyArr[1],copyArr[2]);
NSLog(@"\n深拷贝copy后数组地址:%p\n---元素1:%p\n---元素2:%p\n---元素3:%p\n",  
mutableCopyArr,mutableCopyArr[0],mutableCopyArr[1],mutableCopyArr[2]);

打印结果：源数组地址:0x600000243300
            ---元素1:0x60000000ea80
            ---元素2:0x60000000ea90
            ---元素3:0x60000000eaa0
        浅拷贝copy后数组地址:0x600000243300
            ---元素1:0x60000000ea80
            ---元素2:0x60000000ea90
            ---元素3:0x60000000eaa0
        深拷贝copy后数组地址:0x600000243900
            ---元素1:0x60000000eab0
            ---元素2:0x60000000eaf0
            ---元素3:0x60000000eb00

@interface WGMainObjcVC : UIViewController
@property(nonatomic, strong) NSArray *arr;
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSMutableArray *sourceArr = [NSMutableArray arrayWithObject:@"123"];
    //用可变的数组给arr进行赋值
    self.arr = sourceArr;
    
    //修改sourceArr的元素
    [sourceArr addObject:@"123"];
    
    NSLog(@"arr地址:---%p----arr元素:---%@",self.arr,self.arr);
    NSLog(@"sourceArr地址:---%p----sourceArr元素:---%@",sourceArr,sourceArr);
}

打印结果: arr地址:---0x600000059a70----arr元素:---(123, 123)
            sourceArr地址:---0x600000059a70----sourceArr元素:---(123, 123)