从OC代码转为C++代码查看Category实现

1. 使用命令将OC代码转为CPP

xcrun -sdk iphoneos clang -arch arm64 -rewrite-objc OC源文件 -o 输出CPP文件

1. Category在C++中结构

struct _category_t {
	const char *name;
	struct _class_t *cls;
	const struct _method_list_t *instance_methods;
	const struct _method_list_t *class_methods;
	const struct _protocol_list_t *protocols;
	const struct _prop_list_t *properties;
};

从struct _category_t结构中可以看到分类包含6个元素

• name： 类名，是哪个类的分类
• cls：
• instance_methods：对象方法列表
• class_mehtods：类方法列表
• protocols：遵循的协议列表
• proerties：属性列表

1. 实现一个分类看看转成C++代码，下面是一个NSObject分类Test

   @interface NSObject (Test)<NSCopying, NSMutableCopying>
   
   @property (nonatomic, assign) int age;
   	
   - (void)test01;
   
   + (void)test02;
   
   @end
   
   @implementation NSObject (Test)
   - (void)test01 {}
   
   + (void)test02 {}
   
   - (id)copyWithZone:(nullable NSZone *)zone {return [NSObject new];}
   @end
   

3.1 Test 分类在C++的初始化

static struct _category_t _OBJC_$_CATEGORY_NSObject_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = 
{
	"NSObject",
	0, // &OBJC_CLASS_$_NSObject,
	(const struct _method_list_t *)&_OBJC_$_CATEGORY_INSTANCE_METHODS_NSObject_$_Test,
	(const struct _method_list_t *)&_OBJC_$_CATEGORY_CLASS_METHODS_NSObject_$_Test,
	(const struct _protocol_list_t *)&_OBJC_CATEGORY_PROTOCOLS_$_NSObject_$_Test,
	(const struct _prop_list_t *)&_OBJC_$_PROP_LIST_NSObject_$_Test,
};

• "NSObject"：所属类（name）

• 0, // &OBJC_CLASS_$_NSObject：cls

• (const struct _method_list_t *)&OBJC$CATEGORY_INSTANCE_METHODS_NSObject$_Test : 对象方法列表(instance_methods)

• (const struct _method_list_t *)&OBJC$CATEGORY_CLASS_METHODS_NSObject$_Test：类方法列表(class_mehtods)

• (const struct _protocol_list_t *)&OBJC_CATEGORY_PROTOCOLS$NSObject$_Test：协议列表(protocols)

• (const struct _prop_list_t *)&OBJC$PROP_LIST_NSObject$_Test：属性列表(proerties)

• 从Test分类初始化我们知道了Category存储的内容，现在我们继续分析他们

  • instance_methods

    static struct /*_method_list_t*/ {
    	unsigned int entsize;  // sizeof(struct _objc_method)
    	unsigned int method_count;
    	struct _objc_method method_list[2];
    } _OBJC_$_CATEGORY_INSTANCE_METHODS_NSObject_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {
    	sizeof(_objc_method),
    	2,
    	{{(struct objc_selector *)"test01", "v16@0:8", (void *)_I_NSObject_Test_test01},
    	{(struct objc_selector *)"copyWithZone:", "@24@0:8^{_NSZone=}16", (void *)_I_NSObject_Test_copyWithZone_}}
    };
    

  • class_mehtods

    static struct /*_method_list_t*/ {
    	unsigned int entsize;  // sizeof(struct _objc_method)
    	unsigned int method_count;
    	struct _objc_method method_list[1];
    } _OBJC_$_CATEGORY_CLASS_METHODS_NSObject_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {
    	sizeof(_objc_method),
    	1,
    	{{(struct objc_selector *)"test02", "v16@0:8", (void *)_C_NSObject_Test_test02}}
    };
    

  • protocols

  ------------**NSCopying start**------------
  static const char *_OBJC_PROTOCOL_METHOD_TYPES_NSCopying [] __attribute__ ((used, section ("__DATA,__objc_const"))) = 
  {
  	"@24@0:8^{_NSZone=}16"
  };
  
  static struct /*_method_list_t*/ {
  	unsigned int entsize;  // sizeof(struct _objc_method)
  	unsigned int method_count;
  	struct _objc_method method_list[1];
  } _OBJC_PROTOCOL_INSTANCE_METHODS_NSCopying __attribute__ ((used, section ("__DATA,__objc_const"))) = {
  	sizeof(_objc_method),
  	1,
  	{{(struct objc_selector *)"copyWithZone:", "@24@0:8^{_NSZone=}16", 0}}
  };
  
  struct _protocol_t _OBJC_PROTOCOL_NSCopying __attribute__ ((used)) = {
  	0,
  	"NSCopying",
  	0,
  	(const struct method_list_t *)&_OBJC_PROTOCOL_INSTANCE_METHODS_NSCopying,
  	0,
  	0,
  	0,
  	0,
  	sizeof(_protocol_t),
  	0,
  	(const char **)&_OBJC_PROTOCOL_METHOD_TYPES_NSCopying
  };
  struct _protocol_t *_OBJC_LABEL_PROTOCOL_$_NSCopying = &_OBJC_PROTOCOL_NSCopying;
  ------------**NSCopying end**------------
  
  ------------**NSMutableCopying start**------------
  static const char *_OBJC_PROTOCOL_METHOD_TYPES_NSMutableCopying [] __attribute__ ((used, section ("__DATA,__objc_const"))) = 
  {
  	"@24@0:8^{_NSZone=}16"
  };
  
  static struct /*_method_list_t*/ {
  	unsigned int entsize;  // sizeof(struct _objc_method)
  	unsigned int method_count;
  	struct _objc_method method_list[1];
  } _OBJC_PROTOCOL_INSTANCE_METHODS_NSMutableCopying __attribute__ ((used, section ("__DATA,__objc_const"))) = {
  	sizeof(_objc_method),
  	1,
  	{{(struct objc_selector *)"mutableCopyWithZone:", "@24@0:8^{_NSZone=}16", 0}}
  };
  
  struct _protocol_t _OBJC_PROTOCOL_NSMutableCopying __attribute__ ((used)) = {
  	0,
  	"NSMutableCopying",
  	0,
  	(const struct method_list_t *)&_OBJC_PROTOCOL_INSTANCE_METHODS_NSMutableCopying,
  	0,
  	0,
  	0,
  	0,
  	sizeof(_protocol_t),
  	0,
  	(const char **)&_OBJC_PROTOCOL_METHOD_TYPES_NSMutableCopying
  };
  struct _protocol_t *_OBJC_LABEL_PROTOCOL_$_NSMutableCopying = &_OBJC_PROTOCOL_NSMutableCopying;
  ------------**NSMutableCopying end**------------
  
  ------------**分类中的协议 end**------------
  static struct /*_protocol_list_t*/ {
  	long protocol_count;  // Note, this is 32/64 bit
  	struct _protocol_t *super_protocols[2];
  } _OBJC_CATEGORY_PROTOCOLS_$_NSObject_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {
  	2,
  	&_OBJC_PROTOCOL_NSCopying,
  	&_OBJC_PROTOCOL_NSMutableCopying
  };
  

  • proerties

  static struct /*_prop_list_t*/ {
  	unsigned int entsize;  // sizeof(struct _prop_t)
  	unsigned int count_of_properties;
  	struct _prop_t prop_list[2];
  } _OBJC_$_PROP_LIST_NSObject_$_Test __attribute__ ((used, section ("__DATA,__objc_const"))) = {
  	sizeof(_prop_t),
  	2,
  	{{"age","Ti,N"},
  	{"sex","Ti,N"}}
  };
  

  到这里我们基本知道了Category转为C++中实现，知道了他真实的类型为结构体，接下来我们看看Category在苹果源码中的声明吧

Category在苹果源码中的样子

苹果源码是在不停更新的，这里看到的版本是"818.2"

struct category_t {
    const char *name;
    classref_t cls;
    WrappedPtr<method_list_t, PtrauthStrip> instanceMethods;
    WrappedPtr<method_list_t, PtrauthStrip> classMethods;
    struct protocol_list_t *protocols;
    struct property_list_t *instanceProperties;
    // Fields below this point are not always present on disk.
    struct property_list_t *_classProperties;

    method_list_t *methodsForMeta(bool isMeta) {
        if (isMeta) return classMethods;
        else return instanceMethods;
    }

    property_list_t *propertiesForMeta(bool isMeta, struct header_info *hi);
    
    protocol_list_t *protocolsForMeta(bool isMeta) {
        if (isMeta) return nullptr;
        else return protocols;
    }
};

从源码的表现来看基本上和我们转为C++上一样