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 /*----- Preliminary utilities ---------------------------------------------*/
  36
  37 /* Various hacks for checking compiler versions. */
  38 #define SOD__GCC_P(maj, min)                                            \
  39         (__GNUC__ > (maj) || (__GNUC__ == (maj) && __GNUC_MINOR__ >= (min)))
  40
  41 #ifdef __GNUC__
  42 #  define SOD__EXTENSION __extension__
  43 #else
  44 #  define SOD__EXTENSION
  45 #endif
  46
  47 /* --- @SOD__HAVE_VARARGS_MACROS@ --- *
  48  *
  49  * Use:         Defined if the compiler supports C99-style variadic macros.
  50  *
  51  *              This is more complicated than just checking the value of
  52  *              @__STDC_VERSION__@ because GCC has traditionally claimed C89
  53  *              by default, but provides the functionality anyway unless it's
  54  *              been explicitly turned off.
  55  */
  56
  57 #if __STDC_VERSION__ >= 199901
  58    /* The feature exists.  All is well with the world. */
  59
  60 #  define SOD__HAVE_VARARGS_MACROS
  61
  62 #elif SOD__GCC_P(3, 0)
  63    /* We're using GCC, which is trying to deny it but we don't believe it.
  64     * Unfortunately there's a fly in the ointment: if `-pedantic' -- or,
  65     * worse, `-pedantic-errors' -- is set, then GCC will warn about these
  66     * macros being defined, and there isn't a way to detect pedantry from the
  67     * preprocessor.
  68     *
  69     * We must deploy bodges.  There doesn't seem to be a good way to suppress
  70     * particular warnings from the preprocessor: in particular, messing about
  71     * with `pragma GCC diagnostic' doesn't help.  So we're left with this
  72     * hack: just declare all Sod-generated header files which try to do
  73     * varargs macro things to be `system headers', which means that GCC's
  74     * preprocessor will let them get away with all manner of nefarious stuff.
  75     */
  76
  77 #  define SOD__HAVE_VARARGS_MACROS
  78 #  define SOD__VARARGS_MACROS_PREAMBLE _Pragma("GCC system_header")
  79
  80 #endif
  81
  82 /* Make sure this gratuitous hack is understood, at least vacuously. */
  83 #ifndef SOD__VARARGS_MACROS_PREAMBLE
  84 #  define SOD__VARARGS_MACROS_PREAMBLE
  85 #endif
  86
  87 /* We're going to want to make use of this ourselves. */
  88 SOD__VARARGS_MACROS_PREAMBLE
  89
  90 /* --- @SOD__ALIGNOF@ --- *
  91  *
  92  * Arguments:   @type@ = a C type name, consisting of declaration specifiers
  93  *                      and `*[QUALIFIERS]' declarator operators
  94  *
  95  * Returns:     A sufficient alignment for objects of the given @type@, as a
  96  *              @size_t@.
  97  */
  98
  99 #if __STDC_VERSION__ >= 201112
 100 #  define SOD__ALIGNOF(type) _Alignof(type)
 101 #elif SOD__GCC_P(4, 7)
 102 #  define SOD__ALIGNOF(type) __extension__ _Alignof(type)
 103 #elif defined(__GNUC__)
 104 #  define SOD__ALIGNOF(type) __alignof__(type)
 105 #else
 106 #  define SOD__ALIGNOF(type)                                            \
 107 offsetof(struct { char sod__x; type sod__y; }, sod__y)
 108 #endif
 109
 110 /* --- @SOD__CAR@ --- *
 111  *
 112  * Arguments:   @...@ = a nonempty list of arguments
 113  *
 114  * Returns:     The first argument only.
 115  */
 116
 117 #ifdef SOD__HAVE_VARARGS_MACROS
 118 #  define SOD__CAR(...) SOD__CARx(__VA_LIST__, _)
 119 #  define SOD__CARx(a, ...) a
 120 #endif
 121
 122 /*----- Header files ------------------------------------------------------*/
 123
 124 #include <stdarg.h>
 125 #include <stddef.h>
 126
 127 #include "sod-base.h"
 128
 129 /*----- Data structures ---------------------------------------------------*/
 130
 131 /* A skeletal vtable structure.  At the beginning of every ichain is a
 132  * pointer to one of these.
 133  */
 134 struct sod_vtable {
 135   const SodClass *_class;               /* Pointer to class object */
 136   size_t _base;                         /* Offset to instance base */
 137 };
 138
 139 /* A skeletal instance structure.  Every instance pointer points to one of
 140  * these.
 141  */
 142 struct sod_instance {
 143   const struct sod_vtable *_vt;         /* Pointer to (chain's) vtable */
 144 };
 145
 146 /* Information about a particular chain of superclasses.  In each class,
 147  * there's a pointer to an array of these.  If you search hard enough, you'll
 148  * be able to find out a fair amount of information about an instance and its
 149  * class.
 150  */
 151 struct sod_chain {
 152   size_t n_classes;                     /* Number of classes in chain */
 153   const SodClass *const *classes;       /* Vector of classes, head first */
 154   size_t off_ichain;                    /* Offset of ichain from base */
 155   const struct sod_vtable *vt;          /* Chain's vtable pointer */
 156   size_t ichainsz;                      /* Size of the ichain structure */
 157 };
 158
 159 /*----- Infrastructure macros ---------------------------------------------*/
 160
 161 /* --- @SOD_XCHAIN@ --- *
 162  *
 163  * Arguments:   @chead@ = nickname of target chain's head
 164  *              @obj@ = pointer to an instance chain
 165  *
 166  * Returns:     Pointer to target chain, as a @void *@.
 167  *
 168  * Use:         Utility for implementing cross-chain upcasts.  It's probably
 169  *              not that clever to use this macro directly; it's used to make
 170  *              the automatically-generated upcast macros more palatable.
 171  */
 172
 173 #define SOD_XCHAIN(chead, obj)                                          \
 174   ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
 175
 176 /* --- @SOD_OFFSETDIFF@ --- *
 177  *
 178  * Arguments:   @type@ = a simple (i.e., declaratorless) type name
 179  *              @mema, memb@ = members of @type@
 180  *
 181  * Returns:     The relative offset from @mema@ to @memb@, as a @ptrdiff_t@.
 182  *
 183  * Use:         Computes a signed offset between structure members.
 184  */
 185
 186 #define SOD_OFFSETDIFF(type, mema, memb)                                \
 187   ((ptrdiff_t)offsetof(type, memb) - (ptrdiff_t)offsetof(type, mema))
 188
 189 /* --- @SOD_ILAYOUT@ --- *
 190  *
 191  * Arguments:   @cls@ = name of a class
 192  *              @chead@ = nickname of chain head of @cls@
 193  *              @obj@ = pointer to the @chead@ ichain of an (exact) instance
 194  *                      of @cls@
 195  *
 196  * Returns:     A pointer to the instance's base, cast as a pointer to the
 197  *              ilayout structure.
 198  *
 199  * Use:         Finds an instance's base address given a pointer to one of
 200  *              its ichains, if you know precisely the instance's class and
 201  *              which chain you're pointing to.  If you don't, then (a) you
 202  *              want @SOD_INSTBASE@ below, and (b) you'll have the wrong
 203  *              ilayout anyway.
 204  *
 205  *              This macro is not intended to be used directly outside of
 206  *              automatically generated effective method and trampoline
 207  *              functions, which have the kinds of specific knowledge
 208  *              necessary to use it safely.
 209  */
 210
 211 #define SOD_ILAYOUT(cls, chead, obj)                                    \
 212   ((struct cls##__ilayout *)                                            \
 213    ((char *)(obj) - offsetof(struct cls##__ilayout, chead)))
 214
 215 /*----- Utility macros ----------------------------------------------------*/
 216
 217 /* --- @SOD_CLASSOF@ --- *
 218  *
 219  * Arguments:   @p@ = pointer to an instance chain
 220  *
 221  * Returns:     A pointer to the instance's class, as a @const SodClass *@.
 222  */
 223
 224 #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)
 225
 226 /* --- @SOD_INSTBASE@ --- *
 227  *
 228  * Arguments:   @obj@ = pointer to an instance (i.e., the address of one of
 229  *                      its instance chains)
 230  *
 231  * Returns:     The base address of @obj@'s instance layout, as a @void *@.
 232  *
 233  * Use:         Finds the base address of an instance.  If you know the
 234  *              dynamic class of the object then @SOD_ILAYOUT@ is faster.  If
 235  *              you don't, this is the right macro, but your options for
 236  *              doing something sensible with the result are limited, mostly
 237  *              to simple memory management operations such as freeing or
 238  *              zeroizing the instance structure.
 239  */
 240
 241 #define SOD_INSTBASE(obj) ((void *)((char *)(obj) - (obj)->_vt->_base))
 242
 243 /* --- @SOD_CONVERT@ --- *
 244  *
 245  * Arguments:   @cls@ = a class type name
 246  *              @const void *obj@ = a pointer to an instance
 247  *
 248  * Returns:     Pointer to appropriate instance ichain, or null if the
 249  *              instance isn't of the specified class.
 250  *
 251  * Use:         This is a simple wrapper around the @sod_convert@, which
 252  *              you should see for full details.  It accepts a class type
 253  *              name rather than a pointer to a class object, and arranges to
 254  *              return a pointer of the correct type.
 255  */
 256
 257 #define SOD_CONVERT(cls, obj) ((cls *)sod_convert(cls##__class, (obj)))
 258
 259 /* --- @SOD_DECL@ --- *
 260  *
 261  * Arguments:   @cls_@ = a class type name
 262  *              @var_@ = a variable name
 263  *
 264  * Use:         Declare @var_@ as a pointer to an initialized instance of
 265  *              @cls_@ with automatic lifetime.
 266  */
 267
 268 #define SOD_DECL(cls_, var_)                                            \
 269   struct cls_##__ilayout var_##__layout;                                \
 270   cls_ *var_ = cls_##__class->cls.init(&var_##__layout)
 271
 272 /*----- Functions provided ------------------------------------------------*/
 273
 274 /* --- @sod_subclassp@ --- *
 275  *
 276  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
 277  *
 278  * Returns:     Nonzero if @c@ is a subclass of @d@.
 279  */
 280
 281 extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/);
 282
 283 /* --- @sod_convert@ --- *
 284  *
 285  * Arguments:   @const SodClass *cls@ = desired class object
 286  *              @const void *obj@ = pointer to instance
 287  *
 288  * Returns:     Pointer to appropriate ichain of object, or null if the
 289  *              instance isn't of the specified class.
 290  *
 291  * Use:         General down/cross-casting function.
 292  *
 293  *              Upcasts can be performed efficiently using the automatically
 294  *              generated macros.  In particular, upcasts within a chain are
 295  *              trivial; cross-chain upcasts require information from vtables
 296  *              but are fairly fast.  This function is rather slower, but is
 297  *              much more general.
 298  *
 299  *              Suppose we have an instance of a class C, referred to by a
 300  *              pointer to an instance of one of C's superclasses S.  If T
 301  *              is some other superclass of C then this function will return
 302  *              a pointer to C suitable for use as an instance of T.  If T
 303  *              is not a superclass of C, then the function returns null.
 304  *              (If the pointer doesn't point to an instance of some class
 305  *              then the behaviour is undefined.)  Note that you don't need
 306  *              to know what either C or S actually are.
 307  */
 308
 309 extern void *sod_convert(const SodClass */*cls*/, const void */*obj*/);
 310
 311 /*----- That's all, folks -------------------------------------------------*/
 312
 313 #ifdef __cplusplus
 314   }
 315 #endif
 316
 317 #endif