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1 | /* -*-c-*- |
2 | * | |
3 | * Sensible Object Design header file | |
4 | * | |
5 | * (c) 2009 Straylight/Edgeware | |
6 | */ | |
7 | ||
8 | /*----- Licensing notice --------------------------------------------------* | |
9 | * | |
dea4d055 | 10 | * This file is part of the Sensble Object Design, an object system for C. |
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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 | ||
ddee4bb1 | 39 | #include "sod-base.h" |
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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 { | |
dea4d055 | 47 | const SodClass *_class; /* Pointer to class object */ |
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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 | * @p@ = 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, p) ((char *)(p) + (p)->_vt->_off_##chead) | |
86 | ||
a07d8d00 MW |
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 | ||
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100 | /* --- @SOD_ILAYOUT@ --- * |
101 | * | |
102 | * Arguments: @cls@ = name of a class | |
103 | * @chead@ = nickname of chain head of @cls@ | |
104 | * @p@ = pointer to the @chead@ ichain of an (exact) instance of | |
105 | * @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 | |
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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 | |
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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, p) \ | |
123 | ((struct cls##__ilayout *) \ | |
124 | ((char *)(p) - offsetof(struct cls##__ilayout, chead))) | |
125 | ||
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126 | /* --- @SOD_INSTBASE@ --- * |
127 | * | |
128 | * Arguments: @p@ = pointer to an instance (i.e., the address of one of its | |
129 | * instance chains) | |
130 | * | |
131 | * Returns: The base address of @p@'s instance layout. | |
132 | * | |
133 | * Use: Finds the base address of an instance. If you know the | |
134 | * dynamic class of the object then @SOD_ILAYOUT@ is faster. If | |
135 | * you don't, this is the right macro, but your options for | |
136 | * doing something sensible with the result are limited, mostly | |
137 | * to simple memory management operations such as freeing or | |
138 | * zeroizing the instance structure. | |
139 | */ | |
140 | ||
141 | #define SOD_INSTBASE(p) ((void *)((char *)(p) - (p)->_vt->_base)) | |
142 | ||
77027cca MW |
143 | /*----- Utility macros ----------------------------------------------------*/ |
144 | ||
145 | /* --- @SOD_CLASSOF@ --- * | |
146 | * | |
147 | * Arguments: @p@ = pointer to an instance chain | |
148 | * | |
149 | * Returns: A pointer to the instance's class, as a const SodClass. | |
150 | */ | |
151 | ||
152 | #define SOD_CLASSOF(p) ((const SodClass *)(p)->_vt->_class) | |
153 | ||
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154 | /*----- Functions provided ------------------------------------------------*/ |
155 | ||
77027cca MW |
156 | /* --- @sod_subclassp@ --- * |
157 | * | |
dea4d055 | 158 | * Arguments: @const SodClass *sub, *super@ = pointers to two classes |
77027cca MW |
159 | * |
160 | * Returns: Nonzero if @c@ is a subclass of @d@. | |
161 | */ | |
162 | ||
dea4d055 | 163 | extern int sod_subclassp(const SodClass */*sub*/, const SodClass */*super*/); |
77027cca | 164 | |
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165 | /* --- @sod_convert@ --- * |
166 | * | |
167 | * Arguments: @const SodClass *cls@ = desired class object | |
168 | * @const void *obj@ = pointer to instance | |
169 | * | |
170 | * Returns: Pointer to appropriate ichain of object, or null if the | |
171 | * instance isn't of the specified class. | |
172 | * | |
173 | * Use: General down/cross-casting function. | |
174 | * | |
175 | * Upcasts can be performed efficiently using the automatically | |
dea4d055 | 176 | * generated macros. In particular, upcasts within a chain are |
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177 | * trivial; cross-chain upcasts require information from vtables |
178 | * but are fairly fast. This function is rather slower, but is | |
179 | * much more general. | |
180 | * | |
181 | * Suppose we have an instance of a class C, referred to by a | |
dea4d055 | 182 | * pointer to an instance of one of C's superclasses S. If T |
1f1d88f5 | 183 | * is some other superclass of C then this function will return |
dea4d055 | 184 | * a pointer to C suitable for use as an instance of T. If T |
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185 | * is not a superclass of C, then the function returns null. |
186 | * (If the pointer doesn't point to an instance of some class | |
187 | * then the behaviour is undefined.) Note that you don't need | |
dea4d055 | 188 | * to know what either C or S actually are. |
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189 | */ |
190 | ||
191 | extern void *sod_convert(const SodClass */*cls*/, void */*p*/); | |
192 | ||
193 | /*----- That's all, folks -------------------------------------------------*/ | |
194 | ||
195 | #ifdef __cplusplus | |
196 | } | |
197 | #endif | |
198 | ||
199 | #endif |