Block realizes the essence of-block

The essence of Block:

#import <Foundation/Foundation.h>int  main () {    void(^BLK) (void) =^{ printf ("Block");    Blk ();     return 0 ;}

Use Clang to convert the block.

CLANG-REWRITE-OBJC  Source code files

The block files formed after conversion are:

struct __block_impl {  void *Isa;   int Flags;   int Reserved;   void *funcptr;};

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;

}

};

static void __main_block_func_0 (struct __main_block_impl_0 *__cself) {

printf ("Block");}

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)};

int Main () {

void(*BLK) (void) = ((void (*) ()) &__main_block_impl_0 ( (void *) __main_ Block_func_0, &__main_block_desc_0_data));

((void (*) (__block_impl *)) ((__block_impl *) blk)->funcptr) ((__block_impl *) blk);

return 0;

}

Here's a detailed analysis of these source code:

First we see

^{printf ("Block");

After conversion is called

Static void __main_block_func_0 (struct __main_block_impl_0 *__cself) {printf ("  Block");}

As shown above, the anonymous function used by block is actually converted to the C-language function processing, and the _cself in the function is a pointer to the _MAIN_BLOCK_FUNC_0 struct.

struct __main_block_impl_0 {  struct  __block_impl impl;   struct __main_block_desc_0* desc;

With two member variables, the _BLOCK_IMPLD code is as follows:

struct __block_impl {  void *Isa;   int Flags;   int Reserved;   void *funcptr;};

The second member variable is

__MAIN_BLOCK_DESC_0: The code is as follows:

Static struct __main_block_desc_0 {

SIZE_T reserved;

size_t Block_size;

}

This includes the area required for future version upgrades and the size of the block.

Let's take a look at the code that initializes the struct containing the data:

__main_block_impl_0 (voidstructint flags=0) {    = &_ Nsconcretestackblock;     = flags;     = fp;     = desc;  }

In this case the Nsconcretestackblock is used to initialize, and then we call the constructor:

void (*BLK) (void) = (( Void (*) ()) &__main_block_impl_0 (void *) __main_block_func_0, &_ _main_block_desc_0_data));

Because the conversion is too much to understand, so we get rid of the transformation of the part, so that the result is:

struct _main_block_impl_0 tmp=_main_block_impl_0 (_main_block_func_0,&_main_block_desc_data); struct _main_block_impl_0  *blk=&tmp;

So that we can clearly see that

void (^BLK) (void) =^{printf ("Block");

This statement implements the two variables of _main_block_impl_0, a function function, a desc, and the block type object generated by the block syntax is then assigned to the BLK, which is equivalent to assigning the pointer of the instance to BLK,_MAIN_BLOCK_DESC_ Data is primarily initialized for the size of the _main_block_impl_0 instance of the struct.

Blk ();

This part of the code is converted to

((void (*) (__block_impl *)) ((__block_impl *) blk)->funcptr) ((__block_impl *) blk);

As we get rid of the parts of the transformation are:

(*BLK)->impl. Funcptr (BLK)

This is actually the simplest function pointer call function, as we have just confirmed, in the calling function we see that the block is passed as a parameter.

So what exactly is Nsconcretestackblock?

In order to understand him first we need to understand the OC class and the essence of the object, in fact, the so-called block is the object, "id" This variable is used to store OC object, Nsconcretestackblock is equivalent to C struct body instance, when the block as OC object processing, The information for this class is placed at the Nsconcretestackblock.

Block realizes the essence of-block