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__IGNORE@ --- *
 111  *
 112  * Arguments:   @var@ = some variable name
 113  *
 114  * Use:         Suppress any warning that @var@ isn't used.
 115  */
 116
 117 #define SOD__IGNORE(var) ((void)(var))
 118
 119 /* --- @SOD__CAR@ --- *
 120  *
 121  * Arguments:   @...@ = a nonempty list of arguments
 122  *
 123  * Returns:     The first argument only.
 124  */
 125
 126 #ifdef SOD__HAVE_VARARGS_MACROS
 127 #  define SOD__CAR(...) SOD__CARx(__VA_ARGS__, _)
 128 #  define SOD__CARx(a, ...) a
 129 #endif
 130
 131 /*----- Header files ------------------------------------------------------*/
 132
 133 #include <stdarg.h>
 134 #include <stddef.h>
 135
 136 #include "keyword.h"
 137 #include "sod-base.h"
 138
 139 /*----- Data structures ---------------------------------------------------*/
 140
 141 /* A skeletal vtable structure.  At the beginning of every ichain is a
 142  * pointer to one of these.
 143  */
 144 struct sod_vtable {
 145   const SodClass *_class;               /* Pointer to class object */
 146   size_t _base;                         /* Offset to instance base */
 147 };
 148
 149 /* A skeletal instance structure.  Every instance pointer points to one of
 150  * these.
 151  */
 152 struct sod_instance {
 153   const struct sod_vtable *_vt;         /* Pointer to (chain's) vtable */
 154 };
 155
 156 /* Information about a particular chain of superclasses.  In each class,
 157  * there's a pointer to an array of these.  If you search hard enough, you'll
 158  * be able to find out a fair amount of information about an instance and its
 159  * class.
 160  */
 161 struct sod_chain {
 162   size_t n_classes;                     /* Number of classes in chain */
 163   const SodClass *const *classes;       /* Vector of classes, head first */
 164   size_t off_ichain;                    /* Offset of ichain from base */
 165   const struct sod_vtable *vt;          /* Chain's vtable pointer */
 166   size_t ichainsz;                      /* Size of the ichain structure */
 167 };
 168
 169 /*----- Infrastructure macros ---------------------------------------------*/
 170
 171 /* --- @SOD_XCHAIN@ --- *
 172  *
 173  * Arguments:   @chead@ = nickname of target chain's head
 174  *              @obj@ = pointer to an instance chain
 175  *
 176  * Returns:     Pointer to target chain, as a @void *@.
 177  *
 178  * Use:         Utility for implementing cross-chain upcasts.  It's probably
 179  *              not that clever to use this macro directly; it's used to make
 180  *              the automatically-generated upcast macros more palatable.
 181  */
 182
 183 #define SOD_XCHAIN(chead, obj)                                          \
 184   ((void *)((char *)(obj) + (obj)->_vt->_off_##chead))
 185
 186 /* --- @SOD_OFFSETDIFF@ --- *
 187  *
 188  * Arguments:   @type@ = a simple (i.e., declaratorless) type name
 189  *              @mema, memb@ = members of @type@
 190  *
 191  * Returns:     The relative offset from @mema@ to @memb@, as a @ptrdiff_t@.
 192  *
 193  * Use:         Computes a signed offset between structure members.
 194  */
 195
 196 #define SOD_OFFSETDIFF(type, mema, memb)                                \
 197   ((ptrdiff_t)offsetof(type, memb) - (ptrdiff_t)offsetof(type, mema))
 198
 199 /* --- @SOD_ILAYOUT@ --- *
 200  *
 201  * Arguments:   @cls@ = name of a class
 202  *              @chead@ = nickname of chain head of @cls@
 203  *              @obj@ = pointer to the @chead@ ichain of an (exact) instance
 204  *                      of @cls@
 205  *
 206  * Returns:     A pointer to the instance's base, cast as a pointer to the
 207  *              ilayout structure.
 208  *
 209  * Use:         Finds an instance's base address given a pointer to one of
 210  *              its ichains, if you know precisely the instance's class and
 211  *              which chain you're pointing to.  If you don't, then (a) you
 212  *              want @SOD_INSTBASE@ below, and (b) you'll have the wrong
 213  *              ilayout anyway.
 214  *
 215  *              This macro is not intended to be used directly outside of
 216  *              automatically generated effective method and trampoline
 217  *              functions, which have the kinds of specific knowledge
 218  *              necessary to use it safely.
 219  */
 220
 221 #define SOD_ILAYOUT(cls, chead, obj)                                    \
 222   ((struct cls##__ilayout *)                                            \
 223    ((char *)(obj) - offsetof(struct cls##__ilayout, chead)))
 224
 225 /*----- Utility macros ----------------------------------------------------*/
 226
 227 /* --- @SOD_CLASSOF@ --- *
 228  *
 229  * Arguments:   @p@ = pointer to an instance chain
 230  *
 231  * Returns:     A pointer to the instance's class, as a @const SodClass *@.
 232  */
 233
 234 #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class)
 235
 236 /* --- @SOD_INSTBASE@ --- *
 237  *
 238  * Arguments:   @obj@ = pointer to an instance (i.e., the address of one of
 239  *                      its instance chains)
 240  *
 241  * Returns:     The base address of @obj@'s instance layout, as a @void *@.
 242  *
 243  * Use:         Finds the base address of an instance.  If you know the
 244  *              dynamic class of the object then @SOD_ILAYOUT@ is faster.  If
 245  *              you don't, this is the right macro, but your options for
 246  *              doing something sensible with the result are limited, mostly
 247  *              to simple memory management operations such as freeing or
 248  *              zeroizing the instance structure.
 249  */
 250
 251 #define SOD_INSTBASE(obj) ((void *)((char *)(obj) - (obj)->_vt->_base))
 252
 253 /* --- @SOD_CONVERT@ --- *
 254  *
 255  * Arguments:   @cls@ = a class type name
 256  *              @const void *obj@ = a pointer to an instance
 257  *
 258  * Returns:     Pointer to appropriate instance ichain, or null if the
 259  *              instance isn't of the specified class.
 260  *
 261  * Use:         This is a simple wrapper around the @sod_convert@, which
 262  *              you should see for full details.  It accepts a class type
 263  *              name rather than a pointer to a class object, and arranges to
 264  *              return a pointer of the correct type.
 265  */
 266
 267 #define SOD_CONVERT(cls, obj) ((cls *)sod_convert(cls##__class, (obj)))
 268
 269 /* --- @SOD_INIT@ --- *
 270  *
 271  * Arguments:   @cls@ = a class type name
 272  *              @p@ = pointer to storage to initialize
 273  *              @keys@ = a @KWARGS(...)@ keyword argument sequence
 274  *
 275  * Use:         Initializes raw storage as an instance of @cls@.
 276  */
 277
 278 #define SOD_INIT(cls, p, keys) ((cls *)sod_init(cls##__class, (p), keys))
 279
 280 /* --- @SOD_MAKE@ --- *
 281  *
 282  * Arguments:   @cls@ = a class type name
 283  *              @keys@ = a @KWARGS(...)@ keyword argument sequence
 284  *
 285  * Use:         Allocates (using @malloc@) eand initializes storage to be an
 286  *              instance of @cls@.  Returns a null pointer if allocation
 287  *              fails.  Use @sod_destroy@ to release the instance.
 288  */
 289
 290 #define SOD_MAKE(cls, keys) ((cls *)sod_make(cls##__class, keys))
 291
 292 /* --- @SOD_DECL@ --- *
 293  *
 294  * Arguments:   @cls@ = a class type name
 295  *              @var@ = a variable name
 296  *              @keys@ = a @KWARGS(...)@ keyword argument sequence
 297  *
 298  * Use:         Declare @var@ as a pointer to an initialized instance of
 299  *              @cls@ with automatic lifetime.
 300  */
 301
 302 #define SOD_DECL(cls, var, keys)                                        \
 303   struct cls##__ilayout var##__layout;                                  \
 304   cls *var = (cls *)sod_init(cls##__class, &var##__layout, keys)
 305
 306 /*----- Functions provided ------------------------------------------------*/
 307
 308 /* --- @sod_subclassp@ --- *
 309  *
 310  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
 311  *
 312  * Returns:     Nonzero if @c@ is a subclass of @d@.
 313  */
 314
 315 extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/);
 316
 317 /* --- @sod_convert@ --- *
 318  *
 319  * Arguments:   @const SodClass *cls@ = desired class object
 320  *              @const void *obj@ = pointer to instance
 321  *
 322  * Returns:     Pointer to appropriate ichain of object, or null if the
 323  *              instance isn't of the specified class.
 324  *
 325  * Use:         General down/cross-casting function.
 326  *
 327  *              Upcasts can be performed efficiently using the automatically
 328  *              generated macros.  In particular, upcasts within a chain are
 329  *              trivial; cross-chain upcasts require information from vtables
 330  *              but are fairly fast.  This function is rather slower, but is
 331  *              much more general.
 332  *
 333  *              Suppose we have an instance of a class C, referred to by a
 334  *              pointer to an instance of one of C's superclasses S.  If T
 335  *              is some other superclass of C then this function will return
 336  *              a pointer to C suitable for use as an instance of T.  If T
 337  *              is not a superclass of C, then the function returns null.
 338  *              (If the pointer doesn't point to an instance of some class
 339  *              then the behaviour is undefined.)  Note that you don't need
 340  *              to know what either C or S actually are.
 341  */
 342
 343 extern void *sod_convert(const SodClass */*cls*/, const void */*obj*/);
 344
 345 /* --- @sod_init@, @sod_initv@ --- *
 346  *
 347  * Arguments:   @const SodClass *cls@ = class object for new instance
 348  *              @void *p@ = pointer to storage for new instance
 349  *              @va_list ap, ...@ = initialization keyword arguments
 350  *
 351  * Returns:     Pointer to the initialized instance.
 352  *
 353  * Use:         Initializes an instance in pre-allocated storage, and returns
 354  *              a pointer to it.
 355  *
 356  *              This function will imprint the storage, and then send an
 357  *              `initialize' message to the fresh instance containing the
 358  *              provided keyword arguments.
 359  *
 360  *              It's usually convenient to use the macro @SOD_INIT@ rather
 361  *              than calling @sod_init@ directly.
 362  */
 363
 364 extern KWCALL void *sod_init(const SodClass */*cls*/, void */*p*/, ...);
 365 extern void *sod_initv(const SodClass */*cls*/, void */*p*/, va_list /*ap*/);
 366
 367 /* --- @sod_make@, @sod_makev@ --- *
 368  *
 369  * Arguments:   @const SodClass *cls@ = class object for new instance
 370  *              @va_list ap, ...@ = initialization keyword arguments
 371  *
 372  * Returns:     Pointer to the newly-allocated initialized instance, or null.
 373  *
 374  * Use:         Allocates storage for a new instance, initializes it, and
 375  *              returns a pointer to it.  If allocation fails, a null pointer
 376  *              is returned instead.
 377  *
 378  *              This function will allocate the storage using @malloc@, and
 379  *              then initialize it as for @sod_init@.
 380  *
 381  *              It's usually convenient to use the macro @SOD_MAKE@ rather
 382  *              than calling @sod_make@ directly.
 383  *
 384  *              (This function is not available in freestanding environments
 385  *              lacking @malloc@ and @free@.)
 386  */
 387
 388 extern KWCALL void *sod_make(const SodClass */*cls*/, ...);
 389 extern void *sod_makev(const SodClass */*cls*/, va_list /*ap*/);
 390
 391 /* --- @sod_teardown@ --- *
 392  *
 393  * Arguments:   @void *p@ = pointer to an instance to be torn down
 394  *
 395  * Returns:     Zero if the object is torn down; nonzero if it refused for
 396  *              some reason.
 397  *
 398  * Use:         Invokes the instance's `teardown' method to release any held
 399  *              resources.
 400  *
 401  *              If this function returns nonzero, then the object is still
 402  *              active, and may still hold important resources.  This is not
 403  *              intended to be a failure condition: failures in teardown are
 404  *              usually unrecoverable (or very hard to recover from) and
 405  *              should probably cause the program to abort.  A refusal, on
 406  *              the other hand, means that the object is still live and
 407  *              shouldn't be deallocated, but that this is a normal situation
 408  *              and the caller shouldn't worry about it.
 409  */
 410
 411 extern int sod_teardown(void */*p*/);
 412
 413 /* --- @sod_destroy@ --- *
 414  *
 415  * Arguments:   @void *p@ = pointer to an instance to be torn down, or null
 416  *
 417  * Returns:     Zero if the object was freed; nonzero if it refused for some
 418  *              reason.
 419  *
 420  * Use:         Invokes the instance's `teardown' method to release any held
 421  *              resources, and then calls @free@ to release the instance's
 422  *              storage.  See @sod_teardown@ for details, especially
 423  *              regarding the return value's meaning.
 424  *
 425  *              If @p@ is null, then this function does nothing except
 426  *              returns zero.
 427  *
 428  *              (This function is not available in freestanding environments
 429  *              lacking @malloc@ and @free@.)
 430  */
 431
 432 extern int sod_destroy(void */*p*/);
 433
 434 /*----- That's all, folks -------------------------------------------------*/
 435
 436 #ifdef __cplusplus
 437   }
 438 #endif
 439
 440 #endif