OC源码剖析对象的本质

类的底层实现

先写一个 Person 类:

@interface Person : NSObject

@property (nonatomic, copy) NSString *p_name;

@property (nonatomic, assign) int p_age;

- (void)p_instanceMethod1;

@end

@implementation Person

- (void)p_instanceMethod1{

NSLog(@"%s",__func__);

}

@end

使用 clang 编译器， clang -rewrite-objc Person.m -o Person.cpp  将 Person.m  编译成 Person.cpp 文件，部分代码如下：

/// 1: Person 类型的底层结构

struct NSObject_IMPL {

Class isa;

};

struct Person_IMPL {

struct NSObject_IMPL NSObject_IVARS;

int _p_age;

NSString * _Nonnull _p_name;

};

/// 2: p_name 属性的底层结构

// get

static NSString * _Nonnull _I_Person_p_name(Person * self, SEL _cmd) { return (*(NSString * _Nonnull *)((char *)self + OBJC_IVAR_$_Person$_p_name)); }

extern "C" __declspec(dllimport) void objc_setProperty (id, SEL, long, id, bool, bool);

// set

static void _I_Person_setP_name_(Person * self, SEL _cmd, NSString * _Nonnull p_name) { objc_setProperty (self, _cmd, __OFFSETOFIVAR__(struct Person, _p_name), (id)p_name, 0, 1); }

/// 3: p_age 类型的底层结构

// get

static int _I_Person_p_age(Person * self, SEL _cmd) { return (*(int *)((char *)self + OBJC_IVAR_$_Person$_p_age)); }

// set

static void _I_Person_setP_age_(Person * self, SEL _cmd, int p_age) { (*(int *)((char *)self + OBJC_IVAR_$_Person$_p_age)) = p_age; }

/// 4: p_instanceMethod1 方法的底层结构

static void _I_Person_p_instanceMethod1(Person * self, SEL _cmd) {

NSLog((NSString *)&__NSConstantStringImpl__var_folders_86_0y_j3bzj65z6vw6hy1chw_4m0000gp_T_Person_f010c0_mi_0,__func__);

}