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

   1 /* -*-c-*-
   2  *
   3  * Runtime support for the Sensible Object Design
   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 /*----- Header files ------------------------------------------------------*/
  29
  30 #include "sod.h"
  31
  32 /*----- Main code ---------------------------------------------------------*/
  33
  34 /* --- @find_chain@ --- *
  35  *
  36  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
  37  *
  38  * Returns:     If @sub@ is a subclass of @super@, then a pointer to @sub@'s
  39  *              chain entry describing @super@'s chain; otherwise null.
  40  */
  41
  42 static const struct sod_chain *find_chain(const SodClass *sub,
  43                                           const SodClass *super)
  44 {
  45   const SodClass *head = super->cls.head;
  46   const struct sod_chain *chain, *limit;
  47
  48   /* Slightly fancy footwork.  Each class carries a table describing its
  49    * constituent chains, and each chain has a vector of the classes in that
  50    * chain, with the head (least specific) first.  Chains are always
  51    * non-empty.
  52    *
  53    * Another useful bit of information in the class is its level, i.e., its
  54    * index in its own chain vector.  This is invariant because the chains are
  55    * linear.
  56    *
  57    * This suggests the following algorithm.  Search @sub@'s chains for one
  58    * headed by @super@'s chain head.  If we find one, check that the chain's
  59    * class vector is long enough, and look at the entry corresponding to
  60    * @super@'s level.  If it matches @super@ then @sub@ is indeed a subclass
  61    * and we're done.  Otherwise it isn't, and we lose.  We also lose if no
  62    * matching chain is found.
  63    */
  64   for (chain = sub->cls.chains, limit = chain + sub->cls.n_chains;
  65        chain < limit; chain++) {
  66     if (chain->classes[0] != head)
  67       continue;
  68     if (super->cls.level < chain->n_classes &&
  69         chain->classes[super->cls.level] == super)
  70       return (chain);
  71     break;
  72   }
  73   return (0);
  74 }
  75
  76 /* --- @sod_subclassp@ --- *
  77  *
  78  * Arguments:   @const SodClass *sub, *super@ = pointers to two classes
  79  *
  80  * Returns:     Nonzero if @sub@ is a subclass of @super@.
  81  */
  82
  83 int sod_subclassp(const SodClass *sub, const SodClass *super)
  84   { return (!!find_chain(sub, super)); }
  85
  86 /* --- @sod_convert@ --- *
  87  *
  88  * Arguments:   @const SodClass *cls@ = desired class object
  89  *              @const void *obj@ = pointer to instance
  90  *
  91  * Returns:     Pointer to appropriate ichain of object, or null if the
  92  *              instance isn't of the specified class.
  93  *
  94  * Use:         General down/cross-casting function.
  95  *
  96  *              Upcasts can be performed efficiently using the automatically
  97  *              generated macros.  In particular, upcasts with a chain are
  98  *              trivial; cross-chain upcasts require information from vtables
  99  *              but are fairly fast.  This function is rather slower, but is
 100  *              much more general.
 101  *
 102  *              Suppose we have an instance of a class C, referred to by a
 103  *              pointer to an instance of one of C's superclasses S.  If S'
 104  *              is some other superclass of C then this function will return
 105  *              a pointer to C suitable for use as an instance of S'.  If S'
 106  *              is not a superclass of C, then the function returns null.
 107  *              (If the pointer doesn't point to an instance of some class
 108  *              then the behaviour is undefined.)  Note that you don't need
 109  *              to know what C or S actually are.
 110  */
 111
 112 void *sod_convert(const SodClass *cls, const void *obj)
 113 {
 114   const struct sod_instance *inst = obj;
 115   const struct sod_vtable *vt = inst->_vt;
 116   const SodClass *realcls = vt->_class;
 117   const struct sod_chain *chain = find_chain(realcls, cls);
 118
 119   if (!chain) return (0);
 120   return ((char *)obj - vt->_base + chain->off_ichain);
 121 }
 122
 123 /* --- @sod_init@, @sod_initv@ --- *
 124  *
 125  * Arguments:   @const SodClass *cls@ = class object for new instance
 126  *              @void *p@ = pointer to storage for new instance
 127  *              @va_list ap, ...@ = initialization keyword arguments
 128  *
 129  * Returns:     Pointer to the initialized instance.
 130  *
 131  * Use:         Initializes an instance in pre-allocated storage, and returns
 132  *              a pointer to it.
 133  *
 134  *              This function will imprint the storage, and then send an
 135  *              `initialize' message to the fresh instance containing the
 136  *              provided keyword arguments.
 137  *
 138  *              It's usually convenient to use the macro @SOD_INIT@ rather
 139  *              than calling @sod_init@ directly.
 140  */
 141
 142 void *sod_init(const SodClass *cls, void *p, ...)
 143 {
 144   va_list ap;
 145
 146   va_start(ap, p);
 147   sod_initv(cls, p, ap);
 148   va_end(ap);
 149   return (p);
 150 }
 151
 152 void *sod_initv(const SodClass *cls, void *p, va_list ap)
 153 {
 154   SodObject *obj;
 155
 156   cls->cls.imprint(p);
 157   obj = SOD_CONVERT(SodObject, p);
 158   SodObject_init__v(obj, ap);
 159   return (p);
 160 }
 161
 162 /* --- @sod_teardown@ --- *
 163  *
 164  * Arguments:   @void *p@ = pointer to an instance to be torn down
 165  *
 166  * Returns:     Zero if the object is torn down; nonzero if it refused for
 167  *              some reason.
 168  *
 169  * Use:         Invokes the instance's `teardown' method to release any held
 170  *              resources.
 171  *
 172  *              If this function returns nonzero, then the object is still
 173  *              active, and may still hold important resources.  This is not
 174  *              intended to be a failure condition: failures in teardown are
 175  *              usually unrecoverable (or very hard to recover from) and
 176  *              should probably cause the program to abort.  A refusal, on
 177  *              the other hand, means that the object is still live and
 178  *              shouldn't be deallocated, but that this is a normal situation
 179  *              and the caller shouldn't worry about it.
 180  */
 181
 182 int sod_teardown(void *p)
 183 {
 184   SodObject *obj;
 185
 186   obj = SOD_CONVERT(SodObject, p);
 187   return (SodObject_teardown(obj));
 188 }
 189
 190 /*----- That's all, folks -------------------------------------------------*/