what is the SEL,id and IMP,Class ,Method?

/* Basic data types for Objective C.
   Copyright (C) 1993, 1995, 1996, 2004 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* As a special exception, if you link this library with files
   compiled with GCC to produce an executable, this does not cause
   the resulting executable to be covered by the GNU General Public License.
   This exception does not however invalidate any other reasons why
   the executable file might be covered by the GNU General Public License.  */

#ifndef __objc_INCLUDE_GNU
#define __objc_INCLUDE_GNU

#ifdef __cplusplus
extern "C" {
#endif

#include <stddef.h>

/*
** Definition of the boolean type.  
*/
#ifdef __vxworks
typedef int BOOL;
#else
typedef unsigned char  BOOL;
#endif
#define YES   (BOOL)1
#define NO    (BOOL)0

/*
** Definition of a selector.  Selectors themselves are not unique, but
** the sel_id is a unique identifier.
*/
typedef const struct objc_selector 
{
  void *sel_id;
  const char *sel_types;
} *SEL;

inline static BOOL
sel_eq (SEL s1, SEL s2)
{
  if (s1 == 0 || s2 == 0)
    return s1 == s2;
  else
    return s1->sel_id == s2->sel_id;
}


/*
** ObjC uses this typedef for untyped instances.
*/
typedef struct objc_object {
  struct objc_class*  class_pointer;
} *id;

/*
** Definition of method type.  When retrieving the implementation of a
** method, this is type of the pointer returned.  The idea of the
** definition of IMP is to represent a 'pointer to a general function
** taking an id, a SEL, followed by other unspecified arguments'.  You
** must always cast an IMP to a pointer to a function taking the
** appropriate, specific types for that function, before calling it -
** to make sure the appropriate arguments are passed to it.  The code
** generated by the compiler to perform method calls automatically
** does this cast inside method calls.
*/
typedef id (*IMP)(id, SEL, ...); 

/*
** More simple types...
*/
#define nil (id)0                               /* id of Nil instance */
#define Nil (Class)0                            /* id of Nil class */
typedef char *STR;                              /* String alias */

/*
** The compiler generates one of these structures for each class.  
** 
** This structure is the definition for classes. 
** 
** This structure is generated by the compiler in the executable and used by
** the run-time during normal messaging operations.  Therefore some members
** change type. The compiler generates "char* const" and places a string in
** the following member variables:  super_class. 
*/
typedef struct objc_class *MetaClass;
typedef struct objc_class *Class;
struct objc_class {     
  MetaClass           class_pointer;          /* Pointer to the class's
                                                meta class. */
  struct objc_class*  super_class;            /* Pointer to the super 
                                                class. NULL for class 
                                                Object. */
  const char*         name;                   /* Name of the class. */
  long                version;                /* Unknown. */
  unsigned long       info;                   /* Bit mask.  See class masks 
                                                defined above. */
  long                instance_size;          /* Size in bytes of the class.  
                                                The sum of the class 
                        definition and all super 
                        class definitions. */
  struct objc_ivar_list* ivars;               /* Pointer to a structure that
                                                describes the instance 
                                                variables in the class
                                                definition.  NULL indicates
                                                no instance variables.  Does
                                                not include super class
                                                variables. */
  struct objc_method_list*  methods;          /* Linked list of instance
                                                methods defined for the 
                                                class. */
  struct sarray *    dtable;                  /* Pointer to instance 
                             method dispatch table. */  
  struct objc_class* subclass_list;           /* Subclasses */
  struct objc_class* sibling_class;

  struct objc_protocol_list *protocols;          /* Protocols conformed to */
  void* gc_object_type;
};

#ifndef __OBJC__
typedef struct objc_protocol {
  struct objc_class* class_pointer;
  char *protocol_name;
  struct objc_protocol_list *protocol_list;
  struct objc_method_description_list *instance_methods, *class_methods; 
} Protocol; 

#else /* __OBJC__ */
@class Protocol;
#endif 

typedef void* retval_t;        /* return value */
typedef void(*apply_t)(void);    /* function pointer */
typedef union arglist {
  char *arg_ptr;
  char arg_regs[sizeof (char*)];
} *arglist_t;            /* argument frame */


IMP objc_msg_lookup(id receiver, SEL op);

#ifdef __cplusplus
}
#endif

#endif /* not __objc_INCLUDE_GNU */

struct objc_class {

    struct objc_class super_class;  /*父类*/

    const char *name;                 /*类名字*/

    long version;                   /*版本信息*/

    long info;                        /*类信息*/

    long instance_size;               /*实例大小*/

    struct objc_ivar_list *ivars;     /*实例参数链表*/

    struct objc_method_list **methodLists;  /*方法链表*/

    struct objc_cache *cache;               /*方法缓存*/

    struct objc_protocol_list *protocols;   /*协议链表*/

};

typedef struct objc_method *Method;

typedef struct objc_ method {

    SEL method_name;

    char *method_types;

    IMP method_imp;

};

void (*setter)(id, SEL, BOOL);

int i;

 

setter = (void(*)(id, SEL, BOOL))[target methodForSelector:@selector(setFilled:)];

 

for (i = 0; i < 1000; i++)

    setter(targetList[i], @selector(setFilled:), YES);