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