iOS objc.h
objc属于Objective-C这门语言中的一个重要文件，接下来，我们将逐步解开objc的神秘面纱。
在xcode中打开一个任意一个objc项目，按下shift + command + O组合快捷键，
在"open quickly"搜索框中，输入objc.h, 敲下enter键，即可看到objc.h头文件的内容如下图：
我们在顶部路径区域，操作，点击usr/include可以看到对应iOS结构如下图:
我们可以看到主结构如下:
- Simulator - iOS 14.5
- Frameworks
- DeveloperFrameworks
- usr/include
而objc目录属于usr/include目录中的其中一项，其他挑选一些常见的列举如下:
- usr/include
- 目录
- architecture
- arm
- arm64
- CommonCrypto
- device
- dispatch
- i386
- mach
- mach_debug
- mach-o
- machine
- malloc
- os
- pthread
- secure
- sys
- unicode
- uuid
- voucher
- 独立.h文件
- assert.h
- Block.h
- cache.h
- math.h
- pthread.h
- regex.h
- stdio.h
- sqlite3.h
- 目录
等耳熟能祥的名字. 若是需要研究其他类，可以参考路径来查找对应的文件。
objc目录结构如下:
- objc
- message.h
- module.modulemap
- NSObjCRuntime.h
- NSObject.h
- objc-api.h
- objc-auto.h
- objc-exception.h
- objc-sync.h
- objc.h
- ObjectiveC.apinotes
- runtime.h
其中message.h、NSObject.h、objc.h、runtime.h等文件是最最常见的。
struct objc_class {
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class _Nullable super_class OBJC2_UNAVAILABLE;
const char * _Nonnull name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list * _Nullable ivars OBJC2_UNAVAILABLE;
struct objc_method_list * _Nullable * _Nullable methodLists OBJC2_UNAVAILABLE;
struct objc_cache * _Nonnull cache OBJC2_UNAVAILABLE;
struct objc_protocol_list * _Nullable protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
/* Use `Class` instead of `struct objc_class *` */struct objc_object {
private:
isa_t isa;
public:
// ISA() assumes this is NOT a tagged pointer object
Class ISA();
// getIsa() allows this to be a tagged pointer object
Class getIsa();
// initIsa() should be used to init the isa of new objects only.
// If this object already has an isa, use changeIsa() for correctness.
// initInstanceIsa(): objects with no custom RR/AWZ
// initClassIsa(): class objects
// initProtocolIsa(): protocol objects
// initIsa(): other objects
void initIsa(Class cls /*nonpointer=false*/);
void initClassIsa(Class cls /*nonpointer=maybe*/);
void initProtocolIsa(Class cls /*nonpointer=maybe*/);
void initInstanceIsa(Class cls, bool hasCxxDtor);
// changeIsa() should be used to change the isa of existing objects.
// If this is a new object, use initIsa() for performance.
Class changeIsa(Class newCls);
bool hasNonpointerIsa();
bool isTaggedPointer();
bool isBasicTaggedPointer();
bool isExtTaggedPointer();
bool isClass();
// object may have associated objects?
bool hasAssociatedObjects();
void setHasAssociatedObjects();
// object may be weakly referenced?
bool isWeaklyReferenced();
void setWeaklyReferenced_nolock();
// object may have -.cxx_destruct implementation?
bool hasCxxDtor();
// Optimized calls to retain/release methods
id retain();
void release();
id autorelease();
// Implementations of retain/release methods
id rootRetain();
bool rootRelease();
id rootAutorelease();
bool rootTryRetain();
bool rootReleaseShouldDealloc();
uintptr_t rootRetainCount();
// Implementation of dealloc methods
bool rootIsDeallocating();
void clearDeallocating();
void rootDealloc();
private:
void initIsa(Class newCls, bool nonpointer, bool hasCxxDtor);
// Slow paths for inline control
id rootAutorelease2();
bool overrelease_error();
#if SUPPORT_NONPOINTER_ISA
// Unified retain count manipulation for nonpointer isa
id rootRetain(bool tryRetain, bool handleOverflow);
bool rootRelease(bool performDealloc, bool handleUnderflow);
id rootRetain_overflow(bool tryRetain);
bool rootRelease_underflow(bool performDealloc);
void clearDeallocating_slow();
// Side table retain count overflow for nonpointer isa
void sidetable_lock();
void sidetable_unlock();
void sidetable_moveExtraRC_nolock(size_t extra_rc, bool isDeallocating, bool weaklyReferenced);
bool sidetable_addExtraRC_nolock(size_t delta_rc);
size_t sidetable_subExtraRC_nolock(size_t delta_rc);
size_t sidetable_getExtraRC_nolock();
#endif
// Side-table-only retain count
bool sidetable_isDeallocating();
void sidetable_clearDeallocating();
bool sidetable_isWeaklyReferenced();
void sidetable_setWeaklyReferenced_nolock();
id sidetable_retain();
id sidetable_retain_slow(SideTable& table);
uintptr_t sidetable_release(bool performDealloc = true);
uintptr_t sidetable_release_slow(SideTable& table, bool performDealloc = true);
bool sidetable_tryRetain();
uintptr_t sidetable_retainCount();
#if DEBUG
bool sidetable_present();
#endif
};还可以看到isa_t是一个联合体
union isa_t
{
isa_t() { }
isa_t(uintptr_t value) : bits(value) { }
Class cls;
uintptr_t bits;
#if SUPPORT_PACKED_ISA
// extra_rc must be the MSB-most field (so it matches carry/overflow flags)
// nonpointer must be the LSB (fixme or get rid of it)
// shiftcls must occupy the same bits that a real class pointer would
// bits + RC_ONE is equivalent to extra_rc + 1
// RC_HALF is the high bit of extra_rc (i.e. half of its range)
// future expansion:
// uintptr_t fast_rr : 1; // no r/r overrides
// uintptr_t lock : 2; // lock for atomic property, @synch
// uintptr_t extraBytes : 1; // allocated with extra bytes
# if __arm64__
# define ISA_MASK 0x0000000ffffffff8ULL
# define ISA_MAGIC_MASK 0x000003f000000001ULL
# define ISA_MAGIC_VALUE 0x000001a000000001ULL
struct {
uintptr_t nonpointer : 1;
uintptr_t has_assoc : 1;
uintptr_t has_cxx_dtor : 1;
uintptr_t shiftcls : 33; // MACH_VM_MAX_ADDRESS 0x1000000000
uintptr_t magic : 6;
uintptr_t weakly_referenced : 1;
uintptr_t deallocating : 1;
uintptr_t has_sidetable_rc : 1;
uintptr_t extra_rc : 19;
# define RC_ONE (1ULL<<45)
# define RC_HALF (1ULL<<18)
};
# elif __x86_64__
# define ISA_MASK 0x00007ffffffffff8ULL
# define ISA_MAGIC_MASK 0x001f800000000001ULL
# define ISA_MAGIC_VALUE 0x001d800000000001ULL
struct {
uintptr_t nonpointer : 1;
uintptr_t has_assoc : 1;
uintptr_t has_cxx_dtor : 1;
uintptr_t shiftcls : 44; // MACH_VM_MAX_ADDRESS 0x7fffffe00000
uintptr_t magic : 6;
uintptr_t weakly_referenced : 1;
uintptr_t deallocating : 1;
uintptr_t has_sidetable_rc : 1;
uintptr_t extra_rc : 8;
# define RC_ONE (1ULL<<56)
# define RC_HALF (1ULL<<7)
};
# else
# error unknown architecture for packed isa
# endif
// SUPPORT_PACKED_ISA
#endif
#if SUPPORT_INDEXED_ISA
# if __ARM_ARCH_7K__ >= 2
# define ISA_INDEX_IS_NPI 1
# define ISA_INDEX_MASK 0x0001FFFC
# define ISA_INDEX_SHIFT 2
# define ISA_INDEX_BITS 15
# define ISA_INDEX_COUNT (1 << ISA_INDEX_BITS)
# define ISA_INDEX_MAGIC_MASK 0x001E0001
# define ISA_INDEX_MAGIC_VALUE 0x001C0001
struct {
uintptr_t nonpointer : 1;
uintptr_t has_assoc : 1;
uintptr_t indexcls : 15;
uintptr_t magic : 4;
uintptr_t has_cxx_dtor : 1;
uintptr_t weakly_referenced : 1;
uintptr_t deallocating : 1;
uintptr_t has_sidetable_rc : 1;
uintptr_t extra_rc : 7;
# define RC_ONE (1ULL<<25)
# define RC_HALF (1ULL<<6)
};
# else
# error unknown architecture for indexed isa
# endif
// SUPPORT_INDEXED_ISA
#endif
};struct cache_t {
struct bucket_t *_buckets;
mask_t _mask;
mask_t _occupied;
public:
struct bucket_t *buckets();
mask_t mask();
mask_t occupied();
void incrementOccupied();
void setBucketsAndMask(struct bucket_t *newBuckets, mask_t newMask);
void initializeToEmpty();
mask_t capacity();
bool isConstantEmptyCache();
bool canBeFreed();
static size_t bytesForCapacity(uint32_t cap);
static struct bucket_t * endMarker(struct bucket_t *b, uint32_t cap);
void expand();
void reallocate(mask_t oldCapacity, mask_t newCapacity);
struct bucket_t * find(cache_key_t key, id receiver);
static void bad_cache(id receiver, SEL sel, Class isa) __attribute__((noreturn));
};struct bucket_t {
private:
cache_key_t _key;
IMP _imp;
public:
inline cache_key_t key() const { return _key; }
inline IMP imp() const { return (IMP)_imp; }
inline void setKey(cache_key_t newKey) { _key = newKey; }
inline void setImp(IMP newImp) { _imp = newImp; }
void set(cache_key_t newKey, IMP newImp);
};struct category_t {
const char *name;
classref_t cls;
struct method_list_t *instanceMethods;
struct method_list_t *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);
};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() {
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);
}
bool hasCustomRR() {
return ! bits.hasDefaultRR();
}
void setHasDefaultRR() {
assert(isInitializing());
bits.setHasDefaultRR();
}
void setHasCustomRR(bool inherited = false);
void printCustomRR(bool inherited);
bool hasCustomAWZ() {
return ! bits.hasDefaultAWZ();
}
void setHasDefaultAWZ() {
assert(isInitializing());
bits.setHasDefaultAWZ();
}
void setHasCustomAWZ(bool inherited = false);
void printCustomAWZ(bool inherited);
bool instancesRequireRawIsa() {
return bits.instancesRequireRawIsa();
}
void setInstancesRequireRawIsa(bool inherited = false);
void printInstancesRequireRawIsa(bool inherited);
bool canAllocNonpointer() {
assert(!isFuture());
return !instancesRequireRawIsa();
}
bool canAllocFast() {
assert(!isFuture());
return bits.canAllocFast();
}
bool hasCxxCtor() {
// addSubclass() propagates this flag from the superclass.
assert(isRealized());
return bits.hasCxxCtor();
}
void setHasCxxCtor() {
bits.setHasCxxCtor();
}
bool hasCxxDtor() {
// addSubclass() propagates this flag from the superclass.
assert(isRealized());
return bits.hasCxxDtor();
}
void setHasCxxDtor() {
bits.setHasCxxDtor();
}
bool isSwift() {
return bits.isSwift();
}
// Return YES if the class's ivars are managed by ARC,
// or the class is MRC but has ARC-style weak ivars.
bool hasAutomaticIvars() {
return data()->ro->flags & (RO_IS_ARC | RO_HAS_WEAK_WITHOUT_ARC);
}
// Return YES if the class's ivars are managed by ARC.
bool isARC() {
return data()->ro->flags & RO_IS_ARC;
}
#if SUPPORT_NONPOINTER_ISA
// Tracked in non-pointer isas; not tracked otherwise
#else
bool instancesHaveAssociatedObjects() {
// this may be an unrealized future class in the CF-bridged case
assert(isFuture() || isRealized());
return data()->flags & RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS;
}
void setInstancesHaveAssociatedObjects() {
// this may be an unrealized future class in the CF-bridged case
assert(isFuture() || isRealized());
setInfo(RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS);
}
#endif
bool shouldGrowCache() {
return true;
}
void setShouldGrowCache(bool) {
// fixme good or bad for memory use?
}
bool isInitializing() {
return getMeta()->data()->flags & RW_INITIALIZING;
}
void setInitializing() {
assert(!isMetaClass());
ISA()->setInfo(RW_INITIALIZING);
}
bool isInitialized() {
return getMeta()->data()->flags & RW_INITIALIZED;
}
void setInitialized();
bool isLoadable() {
assert(isRealized());
return true; // any class registered for +load is definitely loadable
}
IMP getLoadMethod();
// Locking: To prevent concurrent realization, hold runtimeLock.
bool isRealized() {
return data()->flags & RW_REALIZED;
}
// Returns true if this is an unrealized future class.
// Locking: To prevent concurrent realization, hold runtimeLock.
bool isFuture() {
return data()->flags & RW_FUTURE;
}
bool isMetaClass() {
assert(this);
assert(isRealized());
return data()->ro->flags & RO_META;
}
// NOT identical to this->ISA when this is a metaclass
Class getMeta() {
if (isMetaClass()) return (Class)this;
else return this->ISA();
}
bool isRootClass() {
return superclass == nil;
}
bool isRootMetaclass() {
return ISA() == (Class)this;
}
const char *mangledName() {
// fixme can't assert locks here
assert(this);
if (isRealized() || isFuture()) {
return data()->ro->name;
} else {
return ((const class_ro_t *)data())->name;
}
}
const char *demangledName(bool realize = false);
const char *nameForLogging();
// May be unaligned depending on class's ivars.
uint32_t unalignedInstanceStart() {
assert(isRealized());
return data()->ro->instanceStart;
}
// Class's instance start rounded up to a pointer-size boundary.
// This is used for ARC layout bitmaps.
uint32_t alignedInstanceStart() {
return word_align(unalignedInstanceStart());
}
// May be unaligned depending on class's ivars.
uint32_t unalignedInstanceSize() {
assert(isRealized());
return data()->ro->instanceSize;
}
// Class's ivar size rounded up to a pointer-size boundary.
uint32_t alignedInstanceSize() {
return word_align(unalignedInstanceSize());
}
size_t instanceSize(size_t extraBytes) {
size_t size = alignedInstanceSize() + extraBytes;
// CF requires all objects be at least 16 bytes.
if (size < 16) size = 16;
return size;
}
void setInstanceSize(uint32_t newSize) {
assert(isRealized());
if (newSize != data()->ro->instanceSize) {
assert(data()->flags & RW_COPIED_RO);
*const_cast<uint32_t *>(&data()->ro->instanceSize) = newSize;
}
bits.setFastInstanceSize(newSize);
}
void chooseClassArrayIndex();
void setClassArrayIndex(unsigned Idx) {
bits.setClassArrayIndex(Idx);
}
unsigned classArrayIndex() {
return bits.classArrayIndex();
}
};参考 https://www.jianshu.com/p/cadf8152c777
https://blog.csdn.net/IOSSHAN/article/details/106228177
objc_class结构体的内容，结合class_rw_t、class_ro_t结构体，可以看出：Class里面有isa、superclass指针，方法列表、属性列表、协议列表以及成员变量列表以及其他信息。 其中，方法列表包含了自己的方法列表以及分类的方法列表，且分类方法列表在原类方法列表前面。
通过操作objc_class里面的bits与上一个定义好的数值，就可以找到class_rw_t里面的内容。这种做法我们在上一篇文章中已经讲解过，用到的是位运算操作，这里不再做叙述。
其中： class_rw_t中的rw是read和write的意思，也就是class_rw_t里面的内容是可读可写的。 class_ro_t中的ro是read和only read的意思，也就是class_ro_t里面的内容是只读的。
接下来我们先来看objc.h有什么信息:
/// An opaque type that represents an Objective-C class.
typedef struct objc_class *Class;
/// Represents an instance of a class.
struct objc_object {
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
};
/// A pointer to an instance of a class.
typedef struct objc_object *id;
#endif
/// An opaque type that represents a method selector.
typedef struct objc_selector *SEL;切换到"runtime.h"中, 看到信息如下:
/// An opaque type that represents a method in a class definition.
typedef struct objc_method *Method;
/// An opaque type that represents an instance variable.
typedef struct objc_ivar *Ivar;
/// An opaque type that represents a category.
typedef struct objc_category *Category;
/// An opaque type that represents an Objective-C declared property.
typedef struct objc_property *objc_property_t;
struct objc_class {
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class _Nullable super_class OBJC2_UNAVAILABLE;
const char * _Nonnull name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list * _Nullable ivars OBJC2_UNAVAILABLE;
struct objc_method_list * _Nullable * _Nullable methodLists OBJC2_UNAVAILABLE;
struct objc_cache * _Nonnull cache OBJC2_UNAVAILABLE;
struct objc_protocol_list * _Nullable protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
/* Use `Class` instead of `struct objc_class *` */
#endif
#ifdef __OBJC__
@class Protocol;
#else
typedef struct objc_object Protocol;
#endif
/// Defines a method
struct objc_method_description {
SEL _Nullable name; /**< The name of the method */
char * _Nullable types; /**< The types of the method arguments */
};
/// Defines a property attribute
typedef struct {
const char * _Nonnull name; /**< The name of the attribute */
const char * _Nonnull value; /**< The value of the attribute (usually empty) */
} objc_property_attribute_t;
可以看出上面的objc.h中常用的Class是objc_class类型的结构体指针，整理几者如下:
typedef struct objc_class *Class;
typedef struct objc_object *id;
typedef struct objc_selector *SEL;runtime.h中
typedef struct objc_method *Method;
typedef struct objc_ivar *Ivar;
typedef struct objc_category *Category;
typedef struct objc_property *objc_property_t;
typedef struct objc_object Protocol;可以看到Class、id、SEL、Method、Ivar、Category、objc_property_t、Protocol等分别对应的结构体指针， 其中objc_object里面内嵌的是Class _Nonnull isa, 也就是我们还是得看objc_class, struct嵌套之多，随处可见; 嵌套之深，复杂异常。
以上都是objc.h头文件对外公开的信息, 我们需要查看objc_class内部信息以及其他更多的信息，就需要查看源码了: objc4, objc4源码的详情信息查看iOS-objc4这篇文章。
打开下载后objc4代码，全局搜索objc_class, 可以看到对应源代码是在
struct objc_class {
Class isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class super_class OBJC2_UNAVAILABLE;
const char *name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list *ivars OBJC2_UNAVAILABLE;
struct objc_method_list **methodLists OBJC2_UNAVAILABLE;
struct objc_cache *cache OBJC2_UNAVAILABLE;
struct objc_protocol_list *protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
/* Use `Class` instead of `struct objc_class *` */可以看到内部还内嵌有其他如objc_ivar_list等结构体，我们先往下深入一下
/// Defines a property attribute
typedef struct {
const char *name; /**< The name of the attribute */
const char *value; /**< The value of the attribute (usually empty) */
} objc_property_attribute_t;https://www.jianshu.com/p/df6629ec9a25
https://www.jianshu.com/p/ead476cdb828 https://www.jianshu.com/p/41735c66dccb
https://juejin.cn/post/6844903639094394893 https://blog.csdn.net/u014773226/article/details/54617716 https://www.jianshu.com/p/62913d6cbc40 https://juejin.cn/post/6844903633113317390 https://juejin.cn/post/6844903600968171533
https://www.jianshu.com/p/f1b2085c4179 https://www.jianshu.com/p/15071d70034e https://www.cnblogs.com/-boy/p/4065783.html https://www.baidu.com/s?wd=oc%20struct%E5%B5%8C%E5%A5%97&rsv_spt=1&rsv_iqid=0xdea253aa0000b849&issp=1&f=8&rsv_bp=1&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_enter=1&rsv_dl=tb&rsv_sug3=24&rsv_sug1=14&rsv_sug7=100&rsv_sug2=0&rsv_btype=i&inputT=8957&rsv_sug4=8957
https://www.baidu.com/s?wd=ios%20property%20syn&rsv_spt=1&rsv_iqid=0x8d5cff410001515e&issp=1&f=8&rsv_bp=1&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_enter=1&rsv_dl=tb&rsv_sug3=23&rsv_sug1=16&rsv_sug7=100&rsv_sug2=0&rsv_btype=i&inputT=12149&rsv_sug4=12149 https://www.jianshu.com/p/50e290f21ff4