引言

我們都知道争舞，一個(gè)類有成員變量凛忿、對(duì)象方法、類方法,那么它們?cè)诘讓邮侨绾螌?shí)現(xiàn)的呢竞川？

前提

要想研究上面內(nèi)容店溢，首先要知道oc對(duì)象在c++層面對(duì)應(yīng)的內(nèi)容叁熔，新創(chuàng)建一個(gè)工程，里面創(chuàng)建一個(gè)Dog類床牧，編譯main.m文件荣回，就會(huì)發(fā)現(xiàn)與main.m同級(jí)的目錄下多了一個(gè)cpp文件。

clang main.m.gif

#import <Foundation/Foundation.h>
@interface Dog : NSObject
@property(nonatomic,copy)NSString*dogName;
-(void)eatFood;
-(void)playWithWhom:(NSString*)name;
@end


#import "Dog.h"
@implementation Dog
-(void)eatFood
{
 NSLog(@"eatFood");
}

-(void)playWithWhom:(NSString*)name
{
 NSLog(@"--%@",name);
}
@end

打開cpp搜索關(guān)鍵字dogName戈咳，可以看出Dog類是一個(gè)結(jié)構(gòu)體Dog_IMPL驹马，我們繼續(xù)看NSObject_IMPL，發(fā)現(xiàn)也是一個(gè)結(jié)構(gòu)體除秀，里面只有isa指針活翩，并沒有我們定義的成員變量和方法挂脑。

image.png

image.png

NSObject在runtime中對(duì)應(yīng)的源碼為

image.png

類對(duì)象的源碼為

image.png

接下來引出我們的重點(diǎn)呐萌，我們可以看出objc_class里最主要的三個(gè)成員變量骑篙。

 Class superclass;       //繼承 objc_object 的ISA    8字節(jié)
 cache_t cache;             // formerly cache pointer and vtable   //16字節(jié)崩瓤，下面有詳解
 class_data_bits_t bits;    // class_rw_t * plus custom rr/alloc flags

其余的全是方法不用考慮俊戳，因?yàn)榉椒ǖ拇鎯?chǔ)是在別的地方陆蟆。

首先寇窑，我們來研究class_data_bits_t bits缎患，通過首地址+指針偏移量來獲取到bits

struct cache_t {
   private:
   explicit_atomic<uintptr_t> _bucketsAndMaybeMask;  //8個(gè)字節(jié)
union {
    struct {
        explicit_atomic<mask_t>    _maybeMask;  //4字節(jié)
   #if __LP64__
        uint16_t                   _flags;                //2字節(jié)
   #endif
        uint16_t                   _occupied;      //2字節(jié)
    }; 
    explicit_atomic<preopt_cache_t *> _originalPreoptCache;   //8個(gè)字節(jié)
};
 ...省略的是一些static變量（全局區(qū)）和方法慕的，沒有影響。
}

由于聯(lián)合體union共用內(nèi)存挤渔，所以union為8個(gè)字節(jié)肮街，所以cache_t為 8 （uintptr_t）+ 8（union）=16字節(jié)。
結(jié)論：想獲取bits的值判导，就是首地址偏移 8+8+16 = 32個(gè)字節(jié)嫉父。
創(chuàng)建一個(gè)類：WJPerson

  #import <Foundation/Foundation.h>

  NS_ASSUME_NONNULL_BEGIN

 @interface WJPerson : NSObject{
     int age;
  }
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) float height;

- (void)playGuitar;
+ (void)eatFood;

// 1: 類的探究分析
// 2: 類方法 + ivar 在哪里

@end

 NS_ASSUME_NONNULL_END


  #import "WJPerson.h"

  @implementation WJPerson

  - (instancetype)init{
     if (self = [super init]) {
          self.name = @"wuji";
       }
   return self;
 }

- (void)playGuitar{

 }
+ (void)eatFood{

 }

 @end

那么，成員變量和方法到底存儲(chǔ)在哪里呢眼刃？
經(jīng)過源碼分析绕辖，我們發(fā)現(xiàn)class_data_bits_t里面有個(gè)data方法，返回的class_rw_t是結(jié)構(gòu)體類型擂红。

 class_rw_t* data() const {
    return (class_rw_t *)(bits & FAST_DATA_MASK);
}

那么class_rw_t里面有什么呢仪际？

 struct class_rw_t {

  const method_array_t methods() const {
       auto v = get_ro_or_rwe();
      if (v.is<class_rw_ext_t *>()) {
        return v.get<class_rw_ext_t *>(&ro_or_rw_ext)->methods;
    } else {
        return method_array_t{v.get<const class_ro_t *>(&ro_or_rw_ext)->baseMethods()};
    }
}

const property_array_t properties() const {
    auto v = get_ro_or_rwe();
    if (v.is<class_rw_ext_t *>()) {
        return v.get<class_rw_ext_t *>(&ro_or_rw_ext)->properties;
    } else {
        return property_array_t{v.get<const class_ro_t *>(&ro_or_rw_ext)->baseProperties};
    }
}

const protocol_array_t protocols() const {
    auto v = get_ro_or_rwe();
    if (v.is<class_rw_ext_t *>()) {
        return v.get<class_rw_ext_t *>(&ro_or_rw_ext)->protocols;
    } else {
        return protocol_array_t{v.get<const class_ro_t *>(&ro_or_rw_ext)->baseProtocols};
    }
}

  //存儲(chǔ)成員變量，比如age
const class_ro_t *ro() const {
    auto v = get_ro_or_rwe();
    if (slowpath(v.is<class_rw_ext_t *>())) {
        return v.get<class_rw_ext_t *>(&ro_or_rw_ext)->ro;
    }
    return v.get<const class_ro_t *>(&ro_or_rw_ext);
}
   ...//里面省略的包括一些copy之類的方法昵骤，這里不做研究
};

那么树碱，method_array_t、property_array_t变秦、protocol_array_t里面會(huì)不會(huì)存儲(chǔ)著我們定義的方法和成員變量呢赴恨？

• property_array_t：

   (lldb) x/4gx WJPerson.class
   0x100004470: 0x0000000100004498 0x0000000100354140
   0x100004480: 0x000000010034b360 0x0000802000000000
  (lldb) p/x 0x100004470+0x20  //首地址（第一個(gè)地址）+ 偏移量32字節(jié)（16進(jìn)制即0x20）
   (long) $5 = 0x0000000100004490
   (lldb) p (class_data_bits_t*)0x0000000100004490
   (class_data_bits_t *) $6 = 0x0000000100004490
  
   (lldb) p $6->data()
   (class_rw_t *) $9 = 0x0000000100706010  //獲取class_rw_t結(jié)構(gòu)體
  (lldb)  p $9->properties()   //獲取properties()
  (const property_array_t) $11 = {
  list_array_tt<property_t, property_list_t, RawPtr> = {
   = {
       list = {
          ptr = 0x0000000100004348
            }
       arrayAndFlag = 4294984520
     }
   }
  }
   (lldb) p $11.list
   (const RawPtr<property_list_t>) $12 = {
    ptr = 0x0000000100004348
   }
    (lldb) p $12.ptr
    (property_list_t *const) $13 = 0x0000000100004348
    (lldb) p   *$13
    (property_list_t) $14 = {
     entsize_list_tt<property_t, property_list_t, 0, PointerModifierNop> = (entsizeAndFlags = 16, count = 2)
  }
   (lldb) p $14.get(0)
   (property_t) $15 = (name = "name", attributes = "T@\"NSString\",C,N,V_name")
   (lldb) p $14.get(1)
   (property_t) $16 = (name = "height", attributes = "Tf,N,V_height")
   (lldb) p $14.get(2)
    Assertion failed: (i < count), function get, file
  

  至此，我們獲取到了屬性name和height,但是我們并沒有看到成員變量age伴栓，為什么伦连，age到底在哪里雨饺，這里放到最后探究。

• method_array_t：

  (lldb) p $9->methods()
  (const method_array_t) $17 = {
  list_array_tt<method_t, method_list_t, method_list_t_authed_ptr> = {
         = {
           list = {
             ptr = 0x0000000100004248
          }
       arrayAndFlag = 4294984264
      }
    }
  }
   (lldb) p $17.list.ptr
   (method_list_t *const) $18 = 0x0000000100004248
   (lldb) p *$18
    (method_list_t) $19 = {
     entsize_list_tt<method_t, method_list_t, 4294901763, method_t::pointer_modifier> =             (entsizeAndFlags = 27, count = 6)
    }
    (lldb) p $19.get(0)
    (method_t) $20 = {}//這個(gè)地方直接get()打印不出來我們想要的結(jié)果了惑淳，下面分析
    (lldb) p $19.get(0).big()
    (method_t::big) $21 = {
      name = "playGuitar"
      types = 0x0000000100003f72 "v16@0:8"
      imp = 0x0000000100003d20 (KCObjcBuild`-[WJPerson playGuitar])
  }
  
  (lldb) p $19.get(1).big()
   (method_t::big) $22 = {
    name = "init"
   types = 0x0000000100003f6a "@16@0:8"
   imp = 0x0000000100003cc0 (KCObjcBuild`-[WJPerson init])
  }
  (lldb) p $19.get(2).big()
  (method_t::big) $23 = {
     name = "name"
     types = 0x0000000100003f6a "@16@0:8"
    imp = 0x0000000100003d30 (KCObjcBuild`-[WJPerson name])
  }
  (lldb) p $19.get(3).big()
  (method_t::big) $24 = {
     name = "height"
     types = 0x0000000100003f89 "f16@0:8"
    imp = 0x0000000100003d90 (KCObjcBuild`-[WJPerson height])
  }
  (lldb) p $19.get(4).big()
  (method_t::big) $25 = {
      name = "setName:"
      types = 0x0000000100003f7a "v24@0:8@16"
      imp = 0x0000000100003d60 (KCObjcBuild`-[WJPerson setName:])
      }
  (lldb) p $19.get(5).big()
  (method_t::big) $26 = {
      name = "setHeight:"
      types = 0x0000000100003f91 "v20@0:8f16"
      imp = 0x0000000100003db0 (KCObjcBuild`-[WJPerson setHeight:])
  }
  (lldb) p $19.get(6).big()
  Assertion failed: (i < count), function get, file
  

至此额港，我們獲取到了- (void)playGuitar，同時(shí)還有name和height的set歧焦、get方法,但是我們并沒有看到+ (void)eatFood移斩，為什么，+ (void)eatFood到底在哪里绢馍，最后探究向瓷。

補(bǔ)充： method_t和property_t調(diào)用get()分析

struct property_t {
      const char *name;

      const char *attributes; //這個(gè)里面有name和attributes可以輸出相關(guān)的信息

  };
 struct method_t {  //這個(gè)里面什么都沒有，但是里面有一個(gè)big結(jié)構(gòu)體舰涌，它的里面有信息猖任。可以通過big()獲取

 struct big {

     SEL name;

     const char *types;

     MethodListIMP imp;

 };
 big &big() const {

 ASSERT(!isSmall());

  return *(struct big *)this;

 }

-vars（成員變量）存儲(chǔ)

(lldb) p $9->ro()
(const class_ro_t *) $34 = 0x0000000100004200
(lldb) p *$34
(const class_ro_t) $35 = {
flags = 0
instanceStart = 8
instanceSize = 24
reserved = 0
  = {
   ivarLayout = 0x0000000000000000
    nonMetaclass = nil
 }
name = {
std::__1::atomic<const char *> = "WJPerson" {
  Value = 0x0000000100003ee4 "WJPerson"
   }
 }
 baseMethodList = 0x0000000100004248
 baseProtocols = 0x0000000000000000
ivars = 0x00000001000042e0
weakIvarLayout = 0x0000000000000000
baseProperties = 0x0000000100004348
_swiftMetadataInitializer_NEVER_USE = {}
}
(lldb) p $35.ivars
(const ivar_list_t *const) $36 = 0x00000001000042e0
(lldb) p *$36
(const ivar_list_t) $37 = {
   entsize_list_tt<ivar_t, ivar_list_t, 0, PointerModifierNop> = (entsizeAndFlags = 32, count = 3)
}
 (lldb) p $37.get(0)
 (ivar_t) $38 = {
 offset = 0x0000000100004408
 name = 0x0000000100003e95 "age"  //這里輸出了age成員變量
 type = 0x0000000100003f85 "i"
  alignment_raw = 2
 size = 4
 }
(lldb) p $37.get(1)
(ivar_t) $39 = {
 offset = 0x0000000100004410
 name = 0x0000000100003e99 "_height"
 type = 0x0000000100003f87 "f"
 alignment_raw = 2
 size = 4
}
(lldb) p $37.get(2)
(ivar_t) $40 = {
 offset = 0x0000000100004418
 name = 0x0000000100003ea1 "_name"
 type = 0x0000000100003f5e "@\"NSString\""
alignment_raw = 3
size = 8
}
(lldb) p $37.get(3)
Assertion failed: (i < count), function get, file

至此瓷耙，我們從ivars獲取到了age朱躺，同時(shí)還有_name和_height。
由上面也可得出一個(gè)結(jié)論：property =ivar + get + set