类的结构里都有什么

类结构分析图

这里直接上图会比较清晰一些，源码的追踪过程这里就不赘述了。主要追踪关键方法objc_class : objc_object。

struct objc_class : objc_object {
    // Class ISA;
    Class superclass;
    cache_t cache;             // formerly cache pointer and vtable
    class_data_bits_t bits;    // class_rw_t * plus custom rr/alloc flags

    class_rw_t *data() const {
        return bits.data();
    }
    void setData(class_rw_t *newData) {
        bits.setData(newData);
    }

    void setInfo(uint32_t set) {
        ASSERT(isFuture()  ||  isRealized());
        data()->setFlags(set);
    }

    void clearInfo(uint32_t clear) {
        ASSERT(isFuture()  ||  isRealized());
        data()->clearFlags(clear);
    }

    // set and clear must not overlap
    void changeInfo(uint32_t set, uint32_t clear) {
        ASSERT(isFuture()  ||  isRealized());
        ASSERT((set & clear) == 0);
        data()->changeFlags(set, clear);
    }
    
    // 此处省略一万行
}

isa

objc_class的第一个成员isa，源码里虽然注释，但也在提醒我们objc_class继承自objc_object,自带了isa特性。isa的流程也已经在上篇文章OC底层-ISA的前生今世分析过了，感兴趣的可以直接去看。占位8字节。

Class superclass

Class superclass表示类的父类，也是8字节。

cache_t cache

cache_t cache表示方法缓存，用散列表来缓存调用过的方法，可以提高访问方法的速度。cache_t cache是方法调用又一巧妙设计，这里只关心它在类中占据的内存大小16字节。

class_data_bits_t bits

class_data_bits_t bits 关键先生存储类的大部分信息，可以类比isa中uintptr bits。

class_rw_t

class_rw_t中存储这属性列表property_array_t properties、实例方法列表method_array_t methods、协议列表protocol_array_t protocols等信息。class_rw_t中这些存储是程序在runtime(运行时)拷贝添加的，它会先将class_ro_t的内容拷贝过去，然后再将当前类的分类的这些属性、方法、协议等拷贝到其中。

class_ro_t

class_ro_t中存储这成员变量列表ivar_list_t ivars、类方法列表method_list_t baseMethodList、协议列表protocol_list_t baseProtocols等信息。class_ro_t中ro的意思是read only，所以class_ro_t存储了当前类在编译期就已经确定的成员变量、类方法以及遵循的协议

验证存储

自定义MuPerson类，代码如下

@interface MuPerson : NSObject
{
    NSString *hobby;// 爱好
    float height;// 身高
}

@property(nonatomic, strong) NSString *name;//姓名
@property(nonatomic, assign) int age;//年龄
@property(nonatomic, assign) BOOL gender;//年龄

-  (void)funcHello;
+ (void)funcWorld;

@end

@implementation MuPerson

-  (void)funcHello{
    NSLog(@"hello");
}

+ (void)funcWorld{
    NSLog(@"world");
}
@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        
        
        // 探究alloc
        MuPerson *person = [MuPerson alloc];
        MuPerson *person1 = [MuPerson alloc];
        NSLog(@"Hello, World!");
    }
    return 0;
}

属性存储

(lldb) p/x MuPerson.class
(Class) $0 = 0x00000001000022d8 MuPerson
(lldb) p/x (class_data_bits_t *)0x00000001000022f8
(class_data_bits_t *) $1 = 0x00000001000022f8
(lldb) p/x *$1
(class_data_bits_t) $2 = (bits = 0x0000000101808474)
(lldb) p/x $1 -> data()
(class_rw_t *) $3 = 0x0000000101808470
(lldb) p/x *$3
(class_rw_t) $4 = {
  flags = 0x80080000
  witness = 0x0000
  ro_or_rw_ext = {
    std::__1::atomic<unsigned long> = 0x0000000100002238
  }
  firstSubclass = nil
  nextSiblingClass = 0x00007fff8cc95448 NSUUID
}
(lldb) p/x $4.ro_or_rw_ext
(explicit_atomic<unsigned long>) $5 = {
  std::__1::atomic<unsigned long> = 0x0000000100002238
}
(lldb) p/x $5.properties
error: <user expression 6>:1:4: no member named 'properties' in 'explicit_atomic<unsigned long>'
$5.properties
~~ ^
(lldb) p/x $4.properties
(const property_array_t) $6 = {
  list_array_tt<property_t, property_list_t> = {
     = {
      list = 0x0000000100002200
      arrayAndFlag = 0x0000000100002200
    }
  }
}
  Fix-it applied, fixed expression was: 
    $4.properties()
(lldb) p/x $6.list
(property_list_t *const) $7 = 0x0000000100002200
(lldb) p/x *$7
(property_list_t) $8 = {
  entsize_list_tt<property_t, property_list_t, 0> = {
    entsizeAndFlags = 0x00000010
    count = 0x00000003
    first = (name = "name", attributes = "T@\"NSString\",&,N,V_name")
  }
}
(lldb) p $8.get(0)
(property_t) $9 = (name = "name", attributes = "T@\"NSString\",&,N,V_name")
(lldb) p $8.get(1)
(property_t) $10 = (name = "age", attributes = "Ti,N,V_age")
(lldb) p $8.get(2)
(property_t) $11 = (name = "gender", attributes = "Tc,N,V_gender")

这里有一个细节，0x00000001000022d8到0x00000001000022f8,指针偏移32位，找到当前类的class_data_bits_t，因为前面isa8字节，Class superclass8字节，cache_t cache16字节。

方法存储

(lldb) p $4.methods
(const method_array_t) $12 = {
  list_array_tt<method_t, method_list_t> = {
     = {
      list = 0x0000000100002090
      arrayAndFlag = 4294975632
    }
  }
}
  Fix-it applied, fixed expression was: 
    $4.methods()
(lldb) p $12.list
(method_list_t *const) $13 = 0x0000000100002090
(lldb) p *$13
(method_list_t) $14 = {
  entsize_list_tt<method_t, method_list_t, 3> = {
    entsizeAndFlags = 26
    count = 8
    first = {
      name = "funcHello"
      types = 0x0000000100000f63 "v16@0:8"
      imp = 0x0000000100000ca0 (MuObjcTest`-[MuPerson funcHello] at MuPerson.m:12)
    }
  }
}
(lldb) p $14.get(0)
(method_t) $15 = {
  name = "funcHello"
  types = 0x0000000100000f63 "v16@0:8"
  imp = 0x0000000100000ca0 (MuObjcTest`-[MuPerson funcHello] at MuPerson.m:12)
}
(lldb) p $14.get(1)
(method_t) $16 = {
  name = ".cxx_destruct"
  types = 0x0000000100000f63 "v16@0:8"
  imp = 0x0000000100000de0 (MuObjcTest`-[MuPerson .cxx_destruct] at MuPerson.m:10)
}
(lldb) p $14.get(2)
(method_t) $17 = {
  name = "name"
  types = 0x0000000100000f6b "@16@0:8"
  imp = 0x0000000100000d00 (MuObjcTest`-[MuPerson name] at MuPerson.h:20)
}
(lldb) p $14.get(3)
(method_t) $18 = {
  name = "setName:"
  types = 0x0000000100000f73 "v24@0:8@16"
  imp = 0x0000000100000d20 (MuObjcTest`-[MuPerson setName:] at MuPerson.h:20)
}
(lldb) p $14.get(4)
(method_t) $19 = {
  name = "age"
  types = 0x0000000100000f7e "i16@0:8"
  imp = 0x0000000100000d60 (MuObjcTest`-[MuPerson age] at MuPerson.h:21)
}
(lldb) p $14.get(5)
(method_t) $20 = {
  name = "gender"
  types = 0x0000000100000f91 "c16@0:8"
  imp = 0x0000000100000da0 (MuObjcTest`-[MuPerson gender] at MuPerson.h:22)
}
(lldb) p $14.get(6)
(method_t) $21 = {
  name = "setGender:"
  types = 0x0000000100000f99 "v20@0:8c16"
  imp = 0x0000000100000dc0 (MuObjcTest`-[MuPerson setGender:] at MuPerson.h:22)
}
(lldb) p $14.get(7)
(method_t) $22 = {
  name = "setAge:"
  types = 0x0000000100000f86 "v20@0:8i16"
  imp = 0x0000000100000d80 (MuObjcTest`-[MuPerson setAge:] at MuPerson.h:21)
}

这里有一个细节，我们的属性，系统默认为我们添加了setter和getter方法

成员变量存储

(lldb) p/x MuPerson.class
(Class) $3 = 0x00000001000022d8 MuPerson
(lldb) p (class_data_bits_t *)0x00000001000022f8
(class_data_bits_t *) $4 = 0x00000001000022f8
(lldb) p $4 -> data()
(class_rw_t *) $5 = 0x00000001010343a0
(lldb) p $5.ro
(const class_ro_t *) $6 = 0x0000000100002238
  Fix-it applied, fixed expression was: 
    $5->ro()
(lldb) p $5 -> ro()
(const class_ro_t *) $7 = 0x0000000100002238
(lldb) p *$7
(const class_ro_t) $8 = {
  flags = 388
  instanceStart = 8
  instanceSize = 40
  reserved = 0
  ivarLayout = 0x0000000100000ef2 "\x01!"
  name = 0x0000000100000ee9 "MuPerson"
  baseMethodList = 0x0000000100002090
  baseProtocols = 0x0000000000000000
  ivars = 0x0000000100002158
  weakIvarLayout = 0x0000000000000000
  baseProperties = 0x0000000100002200
  _swiftMetadataInitializer_NEVER_USE = {}
}
(lldb) p $8.ivars
(const ivar_list_t *const) $9 = 0x0000000100002158
(lldb) p *$9
(const ivar_list_t) $10 = {
  entsize_list_tt<ivar_t, ivar_list_t, 0> = {
    entsizeAndFlags = 32
    count = 5
    first = {
      offset = 0x0000000100002288
      name = 0x0000000100000f43 "hobby"
      type = 0x0000000100000fa4 "@\"NSString\""
      alignment_raw = 3
      size = 8
    }
  }
}
(lldb) p $10.get(0)
(ivar_t) $11 = {
  offset = 0x0000000100002288
  name = 0x0000000100000f43 "hobby"
  type = 0x0000000100000fa4 "@\"NSString\""
  alignment_raw = 3
  size = 8
}
(lldb) p $10.get(1)
(ivar_t) $12 = {
  offset = 0x0000000100002290
  name = 0x0000000100000f49 "height"
  type = 0x0000000100000fb0 "f"
  alignment_raw = 2
  size = 4
}
(lldb) p $10.get(2)
(ivar_t) $13 = {
  offset = 0x0000000100002298
  name = 0x0000000100000f50 "_gender"
  type = 0x0000000100000fb2 "c"
  alignment_raw = 0
  size = 1
}
(lldb) p $10.get(3)
(ivar_t) $14 = {
  offset = 0x00000001000022a0
  name = 0x0000000100000f58 "_age"
  type = 0x0000000100000fb4 "i"
  alignment_raw = 2
  size = 4
}
(lldb) p $10.get(4)
(ivar_t) $15 = {
  offset = 0x00000001000022a8
  name = 0x0000000100000f5d "_name"
  type = 0x0000000100000fa4 "@\"NSString\""
  alignment_raw = 3
  size = 8
}

这里有一个细节，我们的成员变量列表，系统默认为我们添加了_name、_gender和_age成员，由此我们也可以知道属性 =_成员+setter+getter

类方法存储

(lldb) p/x MuPerson.class
(Class) $0 = 0x00000001000022d8 MuPerson
(lldb) x/4gx $0
0x1000022d8: 0x00000001000022b0 0x0000000100333140
0x1000022e8: 0x000000010032d410 0x0000803400000000
(lldb) p/x 0x00000001000022b0 & 0x00007ffffffffff8ULL
(unsigned long long) $1 = 0x00000001000022b0
(lldb) po $1
MuPerson

(lldb) p (class_data_bits_t *)0x00000001000022d0
(class_data_bits_t *) $3 = 0x00000001000022d0
(lldb) p *$3
(class_data_bits_t) $4 = (bits = 4302781876)
(lldb) p $3 -> data()
(class_rw_t *) $5 = 0x0000000100773db0
(lldb) p $5.methods
(const method_array_t) $6 = {
  list_array_tt<method_t, method_list_t> = {
     = {
      list = 0x0000000100002028
      arrayAndFlag = 4294975528
    }
  }
}
  Fix-it applied, fixed expression was: 
    $5->methods()
(lldb) p $6.list
(method_list_t *const) $7 = 0x0000000100002028
(lldb) p *$7
(method_list_t) $8 = {
  entsize_list_tt<method_t, method_list_t, 3> = {
    entsizeAndFlags = 26
    count = 1
    first = {
      name = "funcWorld"
      types = 0x0000000100000f63 "v16@0:8"
      imp = 0x0000000100000cd0 (MuObjcTest`+[MuPerson funcWorld] at MuPerson.m:16)
    }
  }
}
(lldb) p $8.get(0)
(method_t) $9 = {
  name = "funcWorld"
  types = 0x0000000100000f63 "v16@0:8"
  imp = 0x0000000100000cd0 (MuObjcTest`+[MuPerson funcWorld] at MuPerson.m:16)
}

这里有一个细节，类方法是存在我们的元类里，呢对象的类方法其实可以看做是对象的元类的实例化方法。