Runtime

struct method_t {
    SEL name;  // 函数名
    const char *types;  // 编码（返回值类型，参数类型）
    IMP imp;    // 指向函数的指针（函数地址）
};

/// An opaque type that represents a method selector.
typedef struct objc_selector *SEL;

// 获取SEL值的两种方法，同名的选择器都指向相同的地址
NSLog(@"%s, %p", sel_registerName("init"),sel_registerName("init"));
NSLog(@"%s, %p", @selector(init), @selector(init));

// 获取SEL 名
NSLog(@"%@", NSStringFromSelector(@selector(init)));
NSLog(@"%s", sel_getName(@selector(init)));

// types
// 可以使用 @encode来获取不同类型的 type
NSLog(@"%s, %s, %s, %s, %s", @encode(int), @encod(float), @encode(double), @encode(id), @encode(SEL));
// i, f, d, @, :
AYPerson *p = [[AYPerson alloc] init];
AYClass cP = (__bridge AYClass)[p class];
class_rw_t *data = cP->data();
const char *name = sel_getName(data->ro->baseMethodList->first.name);
const char *types =data->ro->baseMethodList->first.types;
NSLog(@"name: %s,    types: %s", name,types);
// name: test2:andB:andString:,    types:v32@0:8i16f20@24
/** 具体的type对照表如下， 第一个v是返回值，32是所有参数占用间的大小，后面依次是
 @0 :8 i16 f20 @24, @0 代表id 从0 开始，:8 代表 SEL 从第8位开始 ...
 */

#if __arm__  ||  __x86_64__  ||  __i386__
// objc_msgSend has few registers available.
// Cache scan increments and wraps at special end-marking bucket.

static inline mask_t cache_next(mask_t i, mask_t mask) {
    return (i+1) & mask;
}
#elif __arm64__
// objc_msgSend has lots of registers available.
// Cache scan decrements. No end marker needed.
static inline mask_t cache_next(mask_t i, mask_t mask) {
    return i ? i-1 : mask;
}
#endif

// Class points to cache. SEL is key. Cache buckets store SEL+IMP.
// Caches are never built in the dyld shared cache.

static inline mask_t cache_hash(SEL sel, mask_t mask) 
{
    return (mask_t)(uintptr_t)sel & mask;
}

bucket_t * cache_t::find(SEL s, id receiver)
{
    assert(s != 0);

    bucket_t *b = buckets();
    mask_t m = mask();
    mask_t begin = cache_hash(s, m);
    mask_t i = begin;
    do {
        if (b[i].sel() == 0  ||  b[i].sel() == s) {
            return &b[i];
        }
    } while ((i = cache_next(i, m)) != begin);
    // 循环一次以后还没有找到，会抛异常
    // hack
    Class cls = (Class)((uintptr_t)this - offsetof(objc_class, cache));
    cache_t::bad_cache(receiver, (SEL)s, cls);
}

void cache_t::expand()
{
    cacheUpdateLock.assertLocked();
    
    uint32_t oldCapacity = capacity();
    uint32_t newCapacity = oldCapacity ? oldCapacity*2 : INIT_CACHE_SIZE;

    if ((uint32_t)(mask_t)newCapacity != newCapacity) {
        // mask overflow - can't grow further
        // fixme this wastes one bit of mask
        newCapacity = oldCapacity;
    }

    reallocate(oldCapacity, newCapacity);
}
void cache_t::reallocate(mask_t oldCapacity, mask_t newCapacity)
{
    bool freeOld = canBeFreed();

    bucket_t *oldBuckets = buckets();
    bucket_t *newBuckets = allocateBuckets(newCapacity);

    // Cache's old contents are not propagated. 
    // This is thought to save cache memory at the cost of extra cache fills.
    // fixme re-measure this

    assert(newCapacity > 0);
    assert((uintptr_t)(mask_t)(newCapacity-1) == newCapacity-1);

    setBucketsAndMask(newBuckets, newCapacity - 1);
    
    if (freeOld) {
        cache_collect_free(oldBuckets, oldCapacity);
        cache_collect(false);
    }
}

/// 方法缓存
        AYPerson *p = [[AYPerson alloc] init];
        AYClass cP = (__bridge AYClass)[p class];

        cache_t pCache = cP->cache;
        for (int i = 0; i < pCache._mask; i++)
        {
            
            NSLog(@"pCache._buckets[%d]->%s", i, pCache._buckets[i]._sel);
        }
        NSLog(@"-------------------");
        /**
         pCache._buckets[0]->(null)
         pCache._buckets[1]->(null)
         pCache._buckets[2]->init
         -------------------
        */
        [p test];
        for (int i = 0; i < pCache._mask; i++)
        {
            
            NSLog(@"pCache._buckets[%d]->%s", i, pCache._buckets[i]._sel);
        }
        NSLog(@"-------------------");
        /**
         pCache._buckets[0]->test
         pCache._buckets[1]->(null)
         pCache._buckets[2]->init
         -------------------
         */
        [p test2:1 andB:2 andString:@"s"];
        for (int i = 0; i < pCache._mask; i++)
        {
            NSLog(@"pCache._buckets[%d]->%s", i, pCache._buckets[i]._sel);
        }
        /**
         pCache._buckets[0]->test
         pCache._buckets[1]->(null)
         pCache._buckets[2]->init
         */
        
        // 查找缓存方法
        bucket_t *b = pCache.cacheFind(@selector(test));
        NSLog(@"查找缓存方法->%s", (char *)b->_sel);
        // 查找缓存方法->test
        

+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    // yourMethod 没有实现的方法
    // other 另外实现的方法
    if (sel == @selector(yourMethod))
    {
        Method m = class_getInstanceMethod(self, @selector(other));
        class_addMethod(self,
                        sel,
                        method_getImplementation(m),
                        method_getTypeEncoding(m));


        // 这里也可以使用imp_implementationWithBlock(id block)来添加方法实现
    }
    
    return [super resolveInstanceMethod: sel];
}

+ (BOOL)resolveClassMethod:(SEL)sel
{
    // yourMethod 没有实现的方法
    // other 另外实现的方法
    if (sel == @selector(yourMethod))
    {
        Method m = class_getClassMethod(self, @selector(other));
          
        class_addMethod(object_getClass(self),
                        sel,
                        method_getImplementation(m),
                        method_getTypeEncoding(m));
    }
    
    return [super resolveClassMethod:sel];
}

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

@implementation Animal
/**
 告诉编译器不用自动生成getter 和 setter 的实现，
 可以等到运行时再动态添加方法实现
 */
@dynamic name;
@end

NSMethodSignature *ms1 = [NSMethodSignature signatureWithObjCTypes:"v@:"];
NSMethodSignature *ms2 = [[[AYPerson alloc] init] methodSignatureForSelector:@selector(yourMethod)];

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

static void _I_AYStudent_test(AYStudent * self, SEL _cmd) {
    ((void (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("AYStudent"))}, sel_registerName("test"));
}

static void _I_AYStudent_test(AYStudent * self, SEL _cmd) {
    objc_msgSendSuper((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("AYStudent"))}, sel_registerName("test"));
}

/** 
 * Sends a message with a simple return value to the superclass of an instance of a class.
 * 
 * @param super A pointer to an \c objc_super data structure. Pass values identifying the
 *  context the message was sent to, including the instance of the class that is to receive the
 *  message and the superclass at which to start searching for the method implementation.
 * @param op A pointer of type SEL. Pass the selector of the method that will handle the message.
 * @param ...
 *   A variable argument list containing the arguments to the method.
 * 
 * @return The return value of the method identified by \e op.
 * 
 * @see objc_msgSend
 */
OBJC_EXPORT id _Nullable
objc_msgSendSuper(struct objc_super * _Nonnull super, SEL _Nonnull op, ...)
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0, 2.0);

/// Specifies the superclass of an instance. 
struct objc_super {
    /// Specifies an instance of a class.
    __unsafe_unretained _Nonnull id receiver;

    /// Specifies the particular superclass of the instance to message. 
#if !defined(__cplusplus)  &&  !__OBJC2__
    /* For compatibility with old objc-runtime.h header */
    __unsafe_unretained _Nonnull Class class;
#else
    __unsafe_unretained _Nonnull Class super_class;
#endif
    /* super_class is the first class to search */
};
#endif

- (Class)class
{
    return object_getClass(self);
}
- (Class)superclass
{
    return class_getSuperclass(object_getClass(self));
}

动态创建一个类（参数：父类，类名，额外的内存空间）
Class objc_allocateClassPair(Class superclass, const char *name, size_t extraBytes)

注册一个类（要在类注册之前添加成员变量）
void objc_registerClassPair(Class cls) 

销毁一个类
void objc_disposeClassPair(Class cls)

获取isa指向的Class
Class object_getClass(id obj)

设置isa指向的Class
Class object_setClass(id obj, Class cls)

判断一个OC对象是否为Class
BOOL object_isClass(id obj)

判断一个Class是否为元类
BOOL class_isMetaClass(Class cls)

获取父类
Class class_getSuperclass(Class cls)

获取一个实例变量信息
Ivar class_getInstanceVariable(Class cls, const char *name)

拷贝实例变量列表（最后需要调用free释放）
Ivar *class_copyIvarList(Class cls, unsigned int *outCount)

设置和获取成员变量的值
void object_setIvar(id obj, Ivar ivar, id value)
id object_getIvar(id obj, Ivar ivar)

动态添加成员变量（已经注册的类是不能动态添加成员变量的）
BOOL class_addIvar(Class cls, const char * name, size_t size, uint8_t alignment, const char * types)

获取成员变量的相关信息
const char *ivar_getName(Ivar v)
const char *ivar_getTypeEncoding(Ivar v)

获取一个属性
objc_property_t class_getProperty(Class cls, const char *name)

拷贝属性列表（最后需要调用free释放）
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)

动态添加属性
BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                  unsigned int attributeCount)

动态替换属性
void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                      unsigned int attributeCount)

获取属性的一些信息
const char *property_getName(objc_property_t property)
const char *property_getAttributes(objc_property_t property)

获得一个实例方法、类方法
Method class_getInstanceMethod(Class cls, SEL name)
Method class_getClassMethod(Class cls, SEL name)

方法实现相关操作
IMP class_getMethodImplementation(Class cls, SEL name) 
IMP method_setImplementation(Method m, IMP imp)
void method_exchangeImplementations(Method m1, Method m2) 

拷贝方法列表（最后需要调用free释放）
Method *class_copyMethodList(Class cls, unsigned int *outCount)

动态添加方法
BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)

动态替换方法
IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)

获取方法的相关信息（带有copy的需要调用free去释放）
SEL method_getName(Method m)
IMP method_getImplementation(Method m)
const char *method_getTypeEncoding(Method m)
unsigned int method_getNumberOfArguments(Method m)
char *method_copyReturnType(Method m)
char *method_copyArgumentType(Method m, unsigned int index)

选择器相关
const char *sel_getName(SEL sel)
SEL sel_registerName(const char *str)

用block作为方法实现
IMP imp_implementationWithBlock(id block)
id imp_getBlock(IMP anImp)
BOOL imp_removeBlock(IMP anImp)