mdw@git.distorted.org.uk Git - sod/blob - lib/sod.h

   1 /* -*-c-*-
   2  *
   3  * Sensible Object Design header file
   4  *
   5  * (c) 2009 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the Sensible Object Design, an object system for C.
  11  *
  12  * The SOD Runtime Library is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * The SOD Runtime is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with SOD; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef SOD_H
  29 #define SOD_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <stdarg.h>
  38 #include <stddef.h>
  39
  40 #include "sod-base.h"
  41
  42 /*----- Data structures ---------------------------------------------------*/
  43
  44 /* A skeletal vtable structure.  At the beginning of every ichain is a
  45  * pointer to one of these.
  46  */
  47 struct sod_vtable {
  48   const SodClass *_class;               /* Pointer to class object */
  49   size_t _base;                         /* Offset to instance base */
  50 };
  51
  52 /* A skeletal instance structure.  Every instance pointer points to one of
  53  * these.
  54  */
  55 struct sod_instance {
  56   const struct sod_vtable *_vt;         /* Pointer to (chain's) vtable */
  57 };
  58
  59 /* Information about a particular chain of superclasses.  In each class,
  60  * there's a pointer to an array of these.  If you search hard enough, you'll
  61  * be able to find out a fair amount of information about an instance and its
  62  * class.
  63  */
  64 struct sod_chain {
  65   size_t n_classes;                     /* Number of classes in chain */
  66   const SodClass *const *classes;       /* Vector of classes, head first */
  67   size_t off_ichain;                    /* Offset of ichain from base */
  68   const struct sod_vtable *vt;          /* Chain's vtable pointer */
  69   size_t ichainsz;                      /* Size of the ichain structure */
  70 };
  71
  72 /*----- Infrastructure macros ---------------------------------------------*/
  73
  74 /* --- @SOD_XCHAIN@ --- *
  75  *
  76  * Arguments:   @chead@ = nickname of target chain's head
  77  *              @obj@ = pointer to an instance chain
  78  *
  79  * Returns:     Pointer to target chain, as a @void *@.
  80  *
  81  * Use:         Utility for implementing cross-chain upcasts.  It's probably
  82  *              not that clever to use this macro directly; it's used to make
  83  *              the automatically-generated upcast macros more palatable.
  84  */
  85
  86 #define SOD_XCHAIN(chead, obj)                                          \
  87   ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
  88
  89 /* --- @SOD_OFFSETDIFF@ --- *
  90  *
  91  * Arguments:   @type@ = a simple (i.e., declaratorless) type name
  92  *              @mema, memb@ = members of @type@
  93  *
  94  * Returns:     The relative offset from @mema@ to @memb@, as a @ptrdiff_t@.
  95  *
  96  * Use:         Computes a signed offset between structure members.
  97  */
  98
  99 #define SOD_OFFSETDIFF(type, mema, memb)                                \
 100   ((ptrdiff_t)offsetof(type, memb) - (ptrdiff_t)offsetof(type, mema))
 101
 102 /* --- @SOD_ILAYOUT@ --- *
 103  *
 104  * Arguments:   @cls@ = name of a class
 105  *              @chead@ = nickname of chain head of @cls@
 106  *              @obj@ = pointer to the @chead@ ichain of an (exact) instance
 107  *                      of @cls@
 108  *
 109  * Returns:     A pointer to the instance's base, cast as a pointer to the
 110  *              ilayout structure.
 111  *
 112  * Use:         Finds an instance's base address given a pointer to one of
 113  *              its ichains, if you know precisely the instance's class and
 114  *              which chain you're pointing to.  If you don't, then (a) you
 115  *              want @SOD_INSTBASE@ below, and (b) you'll have the wrong
 116  *              ilayout anyway.
 117  *
 118  *              This macro is not intended to be used directly outside of
 119  *              automatically generated effective method and trampoline
 120  *              functions, which have the kinds of specific knowledge
 121  *              necessary to use it safely.
 122  */
 123
 124 #define SOD_ILAYOUT(cls, chead, obj)                                    \
 125   ((struct cls##__ilayout *)                                            \
 126    ((char *)(obj) - offsetof(struct cls##__ilayout, chead)))
 127
 128 /* --- @SOD_CAR@ --- *
 129  *
 130  * Arguments:   @...@ = a nonempty list of arguments
 131  *
 132  * Returns:     The first argument only.
 133  */
 134
 135 #if __STDC_VERSION__ >= 199901
 136 #  define SOD_CAR(...) SOD__CARx(__VA_LIST__, _)
 137 #  define SOD__CARx(a, ...) a
 138 #endif
 139
 140 /*----- Utility macros ----------------------------------------------------*/
 141
 142 /* --- @SOD_CLASSOF@ --- *
 143  *
 144  * Arguments:   @p@ = pointer to an instance chain
 145  *
 146  * Returns:     A pointer to the instance's class, as a @const SodClass *@.
 147  */
 148
 149 #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)
 150
 151 /* --- @SOD_INSTBASE@ --- *
 152  *
 153  * Arguments:   @obj@ = pointer to an instance (i.e., the address of one of
 154  *                      its instance chains)
 155  *
 156  * Returns:     The base address of @obj@'s instance layout, as a @void *@.
 157  *
 158  * Use:         Finds the base address of an instance.  If you know the
 159  *              dynamic class of the object then @SOD_ILAYOUT@ is faster.  If
 160  *              you don't, this is the right macro, but your options for
 161  *              doing something sensible with the result are limited, mostly
 162  *              to simple memory management operations such as freeing or
 163  *              zeroizing the instance structure.
 164  */
 165
 166 #define SOD_INSTBASE(obj) ((void *)((char *)(obj) - (obj)->_vt->_base))
 167
 168 /* --- @SOD_CONVERT@ --- *
 169  *
 170  * Arguments:   @cls@ = a class type name
 171  *              @const void *obj@ = a pointer to an instance
 172  *
 173  * Returns:     Pointer to appropriate instance ichain, or null if the
 174  *              instance isn't of the specified class.
 175  *
 176  * Use:         This is a simple wrapper around the @sod_convert@, which
 177  *              you should see for full details.  It accepts a class type
 178  *              name rather than a pointer to a class object, and arranges to
 179  *              return a pointer of the correct type.
 180  */
 181
 182 #define SOD_CONVERT(cls, obj) ((cls *)sod_convert(cls##__class, (obj)))
 183
 184 /* --- @SOD_DECL@ --- *
 185  *
 186  * Arguments:   @cls_@ = a class type name
 187  *              @var_@ = a variable name
 188  *
 189  * Use:         Declare @var_@ as a pointer to an initialized instance of
 190  *              @cls_@ with automatic lifetime.
 191  */
 192
 193 #define SOD_DECL(cls_, var_)                                            \
 194   struct cls_##__ilayout var_##__layout;                                \
 195   cls_ *var_ = cls_##__class->cls.init(&var_##__layout)
 196
 197 /*----- Functions provided ------------------------------------------------*/
 198
 199 /* --- @sod_subclassp@ --- *
 200  *
 201  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
 202  *
 203  * Returns:     Nonzero if @c@ is a subclass of @d@.
 204  */
 205
 206 extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/);
 207
 208 /* --- @sod_convert@ --- *
 209  *
 210  * Arguments:   @const SodClass *cls@ = desired class object
 211  *              @const void *obj@ = pointer to instance
 212  *
 213  * Returns:     Pointer to appropriate ichain of object, or null if the
 214  *              instance isn't of the specified class.
 215  *
 216  * Use:         General down/cross-casting function.
 217  *
 218  *              Upcasts can be performed efficiently using the automatically
 219  *              generated macros.  In particular, upcasts within a chain are
 220  *              trivial; cross-chain upcasts require information from vtables
 221  *              but are fairly fast.  This function is rather slower, but is
 222  *              much more general.
 223  *
 224  *              Suppose we have an instance of a class C, referred to by a
 225  *              pointer to an instance of one of C's superclasses S.  If T
 226  *              is some other superclass of C then this function will return
 227  *              a pointer to C suitable for use as an instance of T.  If T
 228  *              is not a superclass of C, then the function returns null.
 229  *              (If the pointer doesn't point to an instance of some class
 230  *              then the behaviour is undefined.)  Note that you don't need
 231  *              to know what either C or S actually are.
 232  */
 233
 234 extern void *sod_convert(const SodClass */*cls*/, const void */*obj*/);
 235
 236 /*----- That's all, folks -------------------------------------------------*/
 237
 238 #ifdef __cplusplus
 239   }
 240 #endif
 241
 242 #endif