iOS - block - 捕获对象类型

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block - 捕获对象类型

捕获全局/静态对象类型 <TBC?>

OC代码

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSObject *obj = [[NSObject alloc] init];
        NSLog(@"1_obj = %@ - %p", obj, &obj);

        void (^block)(void) = ^{
            NSLog(@"2_obj = %@ - %p", obj, &obj);
        };
        NSLog(@"3_obj = %@ - %p", obj, &obj);

        block();
        NSLog(@"4_obj = %@ - %p", obj, &obj);
    }
    return 0;
}

MRC 输出: 
1_obj = <NSObject: 0x103801d20> - 0x7ffeefbff408
3_obj = <NSObject: 0x103801d20> - 0x7ffeefbff408
2_obj = <NSObject: 0x103801d20> - 0x7ffeefbff3f8 // 捕获了obj瞬时值, 所以是不同的地址, 但也和block一样, 都在栈上 
4_obj = <NSObject: 0x103801d20> - 0x7ffeefbff408

ARC 输出: 
1_obj = <NSObject: 0x103007670> - 0x7ffeefbff408
3_obj = <NSObject: 0x103007670> - 0x7ffeefbff408
2_obj = <NSObject: 0x103007670> - 0x100503e90 // 指针随block拷贝到堆
4_obj = <NSObject: 0x103007670> - 0x7ffeefbff408

C++代码

MRC/ARC下, 编译的C++代码一致:

int main(int argc, const char * argv[]) {
    { __AtAutoreleasePool __autoreleasepool;  /* @autoreleasepool */
        NSObject *obj = ((NSObject *(*)(id, SEL))(void *)objc_msgSend)((id)((NSObject *(*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("NSObject"), sel_registerName("alloc")), sel_registerName("init"));
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_p5_mp3284bs2xb073r91w__n99r0000gn_T_main_9da835_mi_0, obj, &obj);

        void (*block)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, obj, 570425344));
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_p5_mp3284bs2xb073r91w__n99r0000gn_T_main_9da835_mi_2, obj, &obj);

        ((void (*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_p5_mp3284bs2xb073r91w__n99r0000gn_T_main_9da835_mi_3, obj, &obj);
    }
    return 0;
}


struct __main_block_impl_0 {
    struct __block_impl impl;
    struct __main_block_desc_0* Desc;
    NSObject *__strong obj; // 捕获
    // 第3个入参
    __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, NSObject *__strong _obj, int flags=0) : obj(_obj) {
        impl.isa = &_NSConcreteStackBlock;
        impl.Flags = flags;
        impl.FuncPtr = fp;
        Desc = desc;
    }
};


static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
    // 从block结构中获取捕获的变量
    NSObject *__strong obj = __cself->obj; // bound by copy 
    NSLog((NSString *)&__NSConstantStringImpl__var_folders_p5_mp3284bs2xb073r91w__n99r0000gn_T_main_9da835_mi_1, obj, &obj);
}


// block捕获了对象类型的局部变量, desc 增加了 copy 和 dispose 两个函数 (与对象是否可变无关)★
static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
  void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
  void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};


static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {
    _Block_object_assign((void*)&dst->obj, (void*)src->obj, 3/*BLOCK_FIELD_IS_OBJECT*/);
}


static void __main_block_dispose_0(struct __main_block_impl_0*src) {
    _Block_object_dispose((void*)src->obj, 3/*BLOCK_FIELD_IS_OBJECT*/);
}

捕获对象类型的局部变量, 会增加 copy 和 dispose 函数