| 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 Sensble Object Design, an object system for C. |
| 11 | * |
| 12 | * SOD is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU General Public License as published by |
| 14 | * the Free Software Foundation; either version 2 of the License, or |
| 15 | * (at your option) any later version. |
| 16 | * |
| 17 | * SOD 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 General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU General Public License |
| 23 | * along with SOD; if not, write to the Free Software Foundation, |
| 24 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 25 | */ |
| 26 | |
| 27 | #ifndef SOD_H |
| 28 | #define SOD_H |
| 29 | |
| 30 | #ifdef __cplusplus |
| 31 | extern "C" { |
| 32 | #endif |
| 33 | |
| 34 | /*----- Header files ------------------------------------------------------*/ |
| 35 | |
| 36 | #include <stdarg.h> |
| 37 | #include <stddef.h> |
| 38 | |
| 39 | #include "sod-base.h" |
| 40 | |
| 41 | /*----- Data structures ---------------------------------------------------*/ |
| 42 | |
| 43 | /* A skeletal vtable structure. At the beginning of every ichain is a |
| 44 | * pointer to one of these. |
| 45 | */ |
| 46 | struct sod_vtable { |
| 47 | const SodClass *_class; /* Pointer to class object */ |
| 48 | size_t _base; /* Offset to instance base */ |
| 49 | }; |
| 50 | |
| 51 | /* A skeletal instance structure. Every instance pointer points to one of |
| 52 | * these. |
| 53 | */ |
| 54 | struct sod_instance { |
| 55 | struct sod_vtable *_vt; /* Pointer to (chain's) vtable */ |
| 56 | }; |
| 57 | |
| 58 | /* Information about a particular chain of superclasses. In each class, |
| 59 | * there's a pointer to an array of these. If you search hard enough, you'll |
| 60 | * be able to find out a fair amount of information about an instance and its |
| 61 | * class. |
| 62 | */ |
| 63 | struct sod_chain { |
| 64 | size_t n_classes; /* Number of classes in chain */ |
| 65 | const SodClass *const *classes; /* Vector of classes, head first */ |
| 66 | size_t off_ichain; /* Offset of ichain from base */ |
| 67 | const struct sod_vtable *vt; /* Chain's vtable pointer */ |
| 68 | size_t ichainsz; /* Size of the ichain structure */ |
| 69 | }; |
| 70 | |
| 71 | /*----- Infrastructure macros ---------------------------------------------*/ |
| 72 | |
| 73 | /* --- @SOD_XCHAIN@ --- * |
| 74 | * |
| 75 | * Arguments: @chead@ = nickname of target chain's head |
| 76 | * @obj@ = pointer to an instance chain |
| 77 | * |
| 78 | * Returns: Pointer to target chain, as a @char *@. |
| 79 | * |
| 80 | * Use: Utility for implementing cross-chain upcasts. It's probably |
| 81 | * not that clever to use this macro directly; it's used to make |
| 82 | * the automatically-generated upcast macros more palatable. |
| 83 | */ |
| 84 | |
| 85 | #define SOD_XCHAIN(chead, obj) ((char *)(obj) + (obj)->_vt->_off_##chead) |
| 86 | |
| 87 | /* --- @SOD_OFFSETDIFF@ --- * |
| 88 | * |
| 89 | * Arguments: @type@ = a simple (i.e., declaratorless) type name |
| 90 | * @mema, memb@ = members of @type@ |
| 91 | * |
| 92 | * Returns: The relative offset from @mema@ to @memb@, as a @ptrdiff_t@. |
| 93 | * |
| 94 | * Use: Computes a signed offset between structure members. |
| 95 | */ |
| 96 | |
| 97 | #define SOD_OFFSETDIFF(type, mema, memb) \ |
| 98 | ((ptrdiff_t)offsetof(type, memb) - (ptrdiff_t)offsetof(type, mema)) |
| 99 | |
| 100 | /* --- @SOD_ILAYOUT@ --- * |
| 101 | * |
| 102 | * Arguments: @cls@ = name of a class |
| 103 | * @chead@ = nickname of chain head of @cls@ |
| 104 | * @obj@ = pointer to the @chead@ ichain of an (exact) instance |
| 105 | * of @cls@ |
| 106 | * |
| 107 | * Returns: A pointer to the instance's base, cast as a pointer to the |
| 108 | * ilayout structure. |
| 109 | * |
| 110 | * Use: Finds an instance's base address given a pointer to one of |
| 111 | * its ichains, if you know precisely the instance's class and |
| 112 | * which chain you're pointing to. If you don't, then (a) you |
| 113 | * want @SOD_INSTBASE@ below, and (b) you'll have the wrong |
| 114 | * ilayout anyway. |
| 115 | * |
| 116 | * This macro is not intended to be used directly outside of |
| 117 | * automatically generated effective method and trampoline |
| 118 | * functions, which have the kinds of specific knowledge |
| 119 | * necessary to use it safely. |
| 120 | */ |
| 121 | |
| 122 | #define SOD_ILAYOUT(cls, chead, obj) \ |
| 123 | ((struct cls##__ilayout *) \ |
| 124 | ((char *)(obj) - offsetof(struct cls##__ilayout, chead))) |
| 125 | |
| 126 | /*----- Utility macros ----------------------------------------------------*/ |
| 127 | |
| 128 | /* --- @SOD_CLASSOF@ --- * |
| 129 | * |
| 130 | * Arguments: @p@ = pointer to an instance chain |
| 131 | * |
| 132 | * Returns: A pointer to the instance's class, as a const SodClass. |
| 133 | */ |
| 134 | |
| 135 | #define SOD_CLASSOF(obj) ((const SodClass *)(obj)->_vt->_class) |
| 136 | |
| 137 | /* --- @SOD_INSTBASE@ --- * |
| 138 | * |
| 139 | * Arguments: @obj@ = pointer to an instance (i.e., the address of one of |
| 140 | * its instance chains) |
| 141 | * |
| 142 | * Returns: The base address of @obj@'s instance layout, as a @void *@. |
| 143 | * |
| 144 | * Use: Finds the base address of an instance. If you know the |
| 145 | * dynamic class of the object then @SOD_ILAYOUT@ is faster. If |
| 146 | * you don't, this is the right macro, but your options for |
| 147 | * doing something sensible with the result are limited, mostly |
| 148 | * to simple memory management operations such as freeing or |
| 149 | * zeroizing the instance structure. |
| 150 | */ |
| 151 | |
| 152 | #define SOD_INSTBASE(obj) ((void *)((char *)(obj) - (obj)->_vt->_base)) |
| 153 | |
| 154 | /* --- @SOD_CONVERT@ --- * |
| 155 | * |
| 156 | * Arguments: @cls@ = a class type name |
| 157 | * @const void *obj@ = a pointer to an instance |
| 158 | * |
| 159 | * Returns: Pointer to appropriate instance ichain, or null if the |
| 160 | * instance isn't of the specified class. |
| 161 | * |
| 162 | * Use: This is a simple wrapper around the @sod_convert@, which |
| 163 | * you should see for full details. It accepts a class type |
| 164 | * name rather than a pointer to a class object, and arranges to |
| 165 | * return a pointer of the correct type. |
| 166 | */ |
| 167 | |
| 168 | #define SOD_CONVERT(cls, obj) ((cls *)sod_convert(cls##__class, (obj))) |
| 169 | |
| 170 | /*----- Functions provided ------------------------------------------------*/ |
| 171 | |
| 172 | /* --- @sod_subclassp@ --- * |
| 173 | * |
| 174 | * Arguments: @const SodClass *sub, *super@ = pointers to two classes |
| 175 | * |
| 176 | * Returns: Nonzero if @c@ is a subclass of @d@. |
| 177 | */ |
| 178 | |
| 179 | extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/); |
| 180 | |
| 181 | /* --- @sod_convert@ --- * |
| 182 | * |
| 183 | * Arguments: @const SodClass *cls@ = desired class object |
| 184 | * @const void *obj@ = pointer to instance |
| 185 | * |
| 186 | * Returns: Pointer to appropriate ichain of object, or null if the |
| 187 | * instance isn't of the specified class. |
| 188 | * |
| 189 | * Use: General down/cross-casting function. |
| 190 | * |
| 191 | * Upcasts can be performed efficiently using the automatically |
| 192 | * generated macros. In particular, upcasts within a chain are |
| 193 | * trivial; cross-chain upcasts require information from vtables |
| 194 | * but are fairly fast. This function is rather slower, but is |
| 195 | * much more general. |
| 196 | * |
| 197 | * Suppose we have an instance of a class C, referred to by a |
| 198 | * pointer to an instance of one of C's superclasses S. If T |
| 199 | * is some other superclass of C then this function will return |
| 200 | * a pointer to C suitable for use as an instance of T. If T |
| 201 | * is not a superclass of C, then the function returns null. |
| 202 | * (If the pointer doesn't point to an instance of some class |
| 203 | * then the behaviour is undefined.) Note that you don't need |
| 204 | * to know what either C or S actually are. |
| 205 | */ |
| 206 | |
| 207 | extern void *sod_convert(const SodClass */*cls*/, const void */*obj*/); |
| 208 | |
| 209 | /*----- That's all, folks -------------------------------------------------*/ |
| 210 | |
| 211 | #ifdef __cplusplus |
| 212 | } |
| 213 | #endif |
| 214 | |
| 215 | #endif |