Block

作者: 凶猛老鹰 | 来源:发表于2021-05-30 17:53 被阅读0次

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block 初探
Block

一.block本质上也是一个OC对象，它内部也有个isa指针

block是封装了函数调用以及函数调用环境的OC对象

为了保证block内部能够正常访问外部的变量，block有个变量捕获机制

auto: 这个关键字用于声明变量的生存期为自动，即将不在任何类、结构、枚举、联合和函数中定义的变量视为全局变量，而在函数中定义的变量视为局部变量。这个关键字不怎么多写，因为所有的变量默认就是auto的。

static: 存储类指示编译器在程序的生命周期内保持局部变量的存在，而不需要在每次它进入和离开作用域时进行创建和销毁。因此，使用 static 修饰局部变量可以在函数调用之间保持局部变量的值。

通过编译后的代码可以验证

int c=12;

static int d = 13;

struct __main_block_impl_0 {

struct __block_impl impl;

struct __main_block_desc_0* Desc;

inta;

int*b;

__main_block_impl_0(void*fp,struct__main_block_desc_0 *desc,int_a,int*_b,intflags=0) : a(_a), b(_b) {

impl.isa = &_NSConcreteStackBlock;

impl.Flags = flags;

impl.FuncPtr = fp;

Desc = desc;

}

};

staticvoid__main_block_func_0(struct__main_block_impl_0 *__cself) {

inta = __cself->a;// bound by copy

int*b = __cself->b;// bound by copy

NSLog((NSString *)&__NSConstantStringImpl__var_folders_tn_tyzyh17s5kn7yppk11jsw6t40000gn_T_main_2bce02_mi_0,a);

NSLog((NSString *)&__NSConstantStringImpl__var_folders_tn_tyzyh17s5kn7yppk11jsw6t40000gn_T_main_2bce02_mi_1,(*b));

NSLog((NSString *)&__NSConstantStringImpl__var_folders_tn_tyzyh17s5kn7yppk11jsw6t40000gn_T_main_2bce02_mi_2,c);

NSLog((NSString *)&__NSConstantStringImpl__var_folders_tn_tyzyh17s5kn7yppk11jsw6t40000gn_T_main_2bce02_mi_3,d);

}

static struct __main_block_desc_0 {

size_t reserved;

size_t Block_size;

}__main_block_desc_0_DATA= {0,sizeof(struct__main_block_impl_0)};

intmain(intargc,constchar* argv[]) {

/* @autoreleasepool */{ __AtAutoreleasePool __autoreleasepool;

autointa =10;

staticintb =11;

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

a =20;

b =21;

c =22;

d =23;

((void(*)(__block_impl *))((__block_impl *)block)->FuncPtr)((__block_impl *)block);

}

return0;

}