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 "sod-base.h"
  98
  99 /*----- Data structures ---------------------------------------------------*/
 100
 101 /* A skeletal vtable structure.  At the beginning of every ichain is a
 102  * pointer to one of these.
 103  */
 104 struct sod_vtable {
 105   const SodClass *_class;               /* Pointer to class object */
 106   size_t _base;                         /* Offset to instance base */
 107 };
 108
 109 /* A skeletal instance structure.  Every instance pointer points to one of
 110  * these.
 111  */
 112 struct sod_instance {
 113   const struct sod_vtable *_vt;         /* Pointer to (chain's) vtable */
 114 };
 115
 116 /* Information about a particular chain of superclasses.  In each class,
 117  * there's a pointer to an array of these.  If you search hard enough, you'll
 118  * be able to find out a fair amount of information about an instance and its
 119  * class.
 120  */
 121 struct sod_chain {
 122   size_t n_classes;                     /* Number of classes in chain */
 123   const SodClass *const *classes;       /* Vector of classes, head first */
 124   size_t off_ichain;                    /* Offset of ichain from base */
 125   const struct sod_vtable *vt;          /* Chain's vtable pointer */
 126   size_t ichainsz;                      /* Size of the ichain structure */
 127 };
 128
 129 /*----- Infrastructure macros ---------------------------------------------*/
 130
 131 /* --- @SOD_XCHAIN@ --- *
 132  *
 133  * Arguments:   @chead@ = nickname of target chain's head
 134  *              @obj@ = pointer to an instance chain
 135  *
 136  * Returns:     Pointer to target chain, as a @void *@.
 137  *
 138  * Use:         Utility for implementing cross-chain upcasts.  It's probably
 139  *              not that clever to use this macro directly; it's used to make
 140  *              the automatically-generated upcast macros more palatable.
 141  */
 142
 143 #define SOD_XCHAIN(chead, obj)                                          \
 144   ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
 145
 146 /* --- @SOD_OFFSETDIFF@ --- *
 147  *
 148  * Arguments:   @type@ = a simple (i.e., declaratorless) type name
 149  *              @mema, memb@ = members of @type@
 150  *
 151  * Returns:     The relative offset from @mema@ to @memb@, as a @ptrdiff_t@.
 152  *
 153  * Use:         Computes a signed offset between structure members.
 154  */
 155
 156 #define SOD_OFFSETDIFF(type, mema, memb)                                \
 157   ((ptrdiff_t)offsetof(type, memb) - (ptrdiff_t)offsetof(type, mema))
 158
 159 /* --- @SOD_ILAYOUT@ --- *
 160  *
 161  * Arguments:   @cls@ = name of a class
 162  *              @chead@ = nickname of chain head of @cls@
 163  *              @obj@ = pointer to the @chead@ ichain of an (exact) instance
 164  *                      of @cls@
 165  *
 166  * Returns:     A pointer to the instance's base, cast as a pointer to the
 167  *              ilayout structure.
 168  *
 169  * Use:         Finds an instance's base address given a pointer to one of
 170  *              its ichains, if you know precisely the instance's class and
 171  *              which chain you're pointing to.  If you don't, then (a) you
 172  *              want @SOD_INSTBASE@ below, and (b) you'll have the wrong
 173  *              ilayout anyway.
 174  *
 175  *              This macro is not intended to be used directly outside of
 176  *              automatically generated effective method and trampoline
 177  *              functions, which have the kinds of specific knowledge
 178  *              necessary to use it safely.
 179  */
 180
 181 #define SOD_ILAYOUT(cls, chead, obj)                                    \
 182   ((struct cls##__ilayout *)                                            \
 183    ((char *)(obj) - offsetof(struct cls##__ilayout, chead)))
 184
 185 /*----- Utility macros ----------------------------------------------------*/
 186
 187 /* --- @SOD_CLASSOF@ --- *
 188  *
 189  * Arguments:   @p@ = pointer to an instance chain
 190  *
 191  * Returns:     A pointer to the instance's class, as a @const SodClass *@.
 192  */
 193
 194 #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)
 195
 196 /* --- @SOD_INSTBASE@ --- *
 197  *
 198  * Arguments:   @obj@ = pointer to an instance (i.e., the address of one of
 199  *                      its instance chains)
 200  *
 201  * Returns:     The base address of @obj@'s instance layout, as a @void *@.
 202  *
 203  * Use:         Finds the base address of an instance.  If you know the
 204  *              dynamic class of the object then @SOD_ILAYOUT@ is faster.  If
 205  *              you don't, this is the right macro, but your options for
 206  *              doing something sensible with the result are limited, mostly
 207  *              to simple memory management operations such as freeing or
 208  *              zeroizing the instance structure.
 209  */
 210
 211 #define SOD_INSTBASE(obj) ((void *)((char *)(obj) - (obj)->_vt->_base))
 212
 213 /* --- @SOD_CONVERT@ --- *
 214  *
 215  * Arguments:   @cls@ = a class type name
 216  *              @const void *obj@ = a pointer to an instance
 217  *
 218  * Returns:     Pointer to appropriate instance ichain, or null if the
 219  *              instance isn't of the specified class.
 220  *
 221  * Use:         This is a simple wrapper around the @sod_convert@, which
 222  *              you should see for full details.  It accepts a class type
 223  *              name rather than a pointer to a class object, and arranges to
 224  *              return a pointer of the correct type.
 225  */
 226
 227 #define SOD_CONVERT(cls, obj) ((cls *)sod_convert(cls##__class, (obj)))
 228
 229 /* --- @SOD_DECL@ --- *
 230  *
 231  * Arguments:   @cls_@ = a class type name
 232  *              @var_@ = a variable name
 233  *
 234  * Use:         Declare @var_@ as a pointer to an initialized instance of
 235  *              @cls_@ with automatic lifetime.
 236  */
 237
 238 #define SOD_DECL(cls_, var_)                                            \
 239   struct cls_##__ilayout var_##__layout;                                \
 240   cls_ *var_ = cls_##__class->cls.init(&var_##__layout)
 241
 242 /*----- Functions provided ------------------------------------------------*/
 243
 244 /* --- @sod_subclassp@ --- *
 245  *
 246  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
 247  *
 248  * Returns:     Nonzero if @c@ is a subclass of @d@.
 249  */
 250
 251 extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/);
 252
 253 /* --- @sod_convert@ --- *
 254  *
 255  * Arguments:   @const SodClass *cls@ = desired class object
 256  *              @const void *obj@ = pointer to instance
 257  *
 258  * Returns:     Pointer to appropriate ichain of object, or null if the
 259  *              instance isn't of the specified class.
 260  *
 261  * Use:         General down/cross-casting function.
 262  *
 263  *              Upcasts can be performed efficiently using the automatically
 264  *              generated macros.  In particular, upcasts within a chain are
 265  *              trivial; cross-chain upcasts require information from vtables
 266  *              but are fairly fast.  This function is rather slower, but is
 267  *              much more general.
 268  *
 269  *              Suppose we have an instance of a class C, referred to by a
 270  *              pointer to an instance of one of C's superclasses S.  If T
 271  *              is some other superclass of C then this function will return
 272  *              a pointer to C suitable for use as an instance of T.  If T
 273  *              is not a superclass of C, then the function returns null.
 274  *              (If the pointer doesn't point to an instance of some class
 275  *              then the behaviour is undefined.)  Note that you don't need
 276  *              to know what either C or S actually are.
 277  */
 278
 279 extern void *sod_convert(const SodClass */*cls*/, const void */*obj*/);
 280
 281 /*----- That's all, folks -------------------------------------------------*/
 282
 283 #ifdef __cplusplus
 284   }
 285 #endif
 286
 287 #endif