OC中block对于变量的捕获

block中对于变量的捕获分为三种: 值传递、指针传递和直接访问

值传递

block捕获的局部变量，用auto修饰的，auto一般省略

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        int age = 10;
        void (^block)(void) = ^{
            NSLog(@"%d",age);
        };
        block();
    }
    return 0;
}

转为C++代码如下:

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int age;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _age, int flags=0) : age(_age) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
void (*block)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, age));

这种直接捕获的age的值，为值传递

指针传递

block捕获局部的静态变量

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        static int age = 10;
        void (^block)(void) = ^{
            NSLog(@"%d",age);
        };
        block();
    }
    return 0;
}

转为C++代码:

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int *age;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int *_age, int flags=0) : age(_age) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};

 void (*block)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, &age));

直接获取

block捕获全局变量

#import <Foundation/Foundation.h>

int age = 10;

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        void (^block)(void) = ^{
            NSLog(@"%d",age);
        };
        block();
    }
    return 0;
}

转C++代码如下:

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};

void (*block)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));