1 #ifndef CCAN_CAST_IF_TYPE_H
2 #define CCAN_CAST_IF_TYPE_H
5 #if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
7 * cast_if_type - only cast an expression if test matches a given type
8 * @desttype: the type to cast to
9 * @expr: the expression to cast
10 * @test: the expression to test
11 * @oktype: the type we allow
13 * This macro is used to create functions which allow multiple types.
14 * The result of this macro is used somewhere that a @desttype type is
15 * expected: if @expr was of type @oktype, it will be cast to
16 * @desttype type. As a result, if @expr is any type other than
17 * @oktype or @desttype, a compiler warning will be issued.
19 * This macro can be used in static initializers.
21 * This is merely useful for warnings: if the compiler does not
22 * support the primitives required for cast_if_type(), it becomes an
23 * unconditional cast, and the @test and @oktype argument is not used. In
24 * particular, this means that @oktype can be a type which uses
25 * the "typeof": it will not be evaluated if typeof is not supported.
28 * // We can take either an unsigned long or a void *.
29 * void _set_some_value(void *val);
30 * #define set_some_value(e) \
31 * _set_some_value(cast_if_type(void *, (e), (e), unsigned long))
33 #define cast_if_type(desttype, expr, test, oktype) \
34 __builtin_choose_expr(__builtin_types_compatible_p(typeof(1?(test):0), oktype), \
35 (desttype)(expr), (expr))
37 #define cast_if_type(desttype, expr, test, oktype) ((desttype)(expr))
41 * cast_if_any - only cast an expression if it is one of the three given types
42 * @desttype: the type to cast to
43 * @expr: the expression to cast
44 * @test: the expression to test
45 * @ok1: the first type we allow
46 * @ok2: the second type we allow
47 * @ok3: the third type we allow
49 * This is a convenient wrapper for multiple cast_if_type() calls. You can
50 * chain them inside each other (ie. use cast_if_any() for expr) if you need
51 * more than 3 arguments.
54 * // We can take either a long, unsigned long, void * or a const void *.
55 * void _set_some_value(void *val);
56 * #define set_some_value(expr) \
57 * _set_some_value(cast_if_any(void *, (expr), (expr), \
58 * long, unsigned long, const void *))
60 #define cast_if_any(desttype, expr, test, ok1, ok2, ok3) \
61 cast_if_type(desttype, \
62 cast_if_type(desttype, \
63 cast_if_type(desttype, (expr), (test), ok1), \
68 * typesafe_cb - cast a callback function if it matches the arg
69 * @rtype: the return type of the callback function
70 * @fn: the callback function to cast
71 * @arg: the (pointer) argument to hand to the callback function.
73 * If a callback function takes a single argument, this macro does
74 * appropriate casts to a function which takes a single void * argument if the
75 * callback provided matches the @arg (or a const or volatile version).
77 * It is assumed that @arg is of pointer type: usually @arg is passed
78 * or assigned to a void * elsewhere anyway.
81 * void _register_callback(void (*fn)(void *arg), void *arg);
82 * #define register_callback(fn, arg) \
83 * _register_callback(typesafe_cb(void, (fn), (arg)), (arg))
85 #define typesafe_cb(rtype, fn, arg) \
86 cast_if_type(rtype (*)(void *), (fn), (fn)(arg), rtype)
89 * typesafe_cb_const - cast a const callback function if it matches the arg
90 * @rtype: the return type of the callback function
91 * @fn: the callback function to cast
92 * @arg: the (pointer) argument to hand to the callback function.
94 * If a callback function takes a single argument, this macro does appropriate
95 * casts to a function which takes a single const void * argument if the
96 * callback provided matches the @arg.
98 * It is assumed that @arg is of pointer type: usually @arg is passed
99 * or assigned to a void * elsewhere anyway.
102 * void _register_callback(void (*fn)(const void *arg), const void *arg);
103 * #define register_callback(fn, arg) \
104 * _register_callback(typesafe_cb_const(void, (fn), (arg)), (arg))
106 #define typesafe_cb_const(rtype, fn, arg) \
107 sizeof((fn)((const void *)0)), \
108 cast_if_type(rtype (*)(const void *), \
109 (fn), (fn)(arg), rtype (*)(typeof(arg)))
112 * typesafe_cb_preargs - cast a callback function if it matches the arg
113 * @rtype: the return type of the callback function
114 * @fn: the callback function to cast
115 * @arg: the (pointer) argument to hand to the callback function.
117 * This is a version of typesafe_cb() for callbacks that take other arguments
121 * void _register_callback(void (*fn)(int, void *arg), void *arg);
122 * #define register_callback(fn, arg) \
123 * _register_callback(typesafe_cb_preargs(void, (fn), (arg), int),\
126 #define typesafe_cb_preargs(rtype, fn, arg, ...) \
127 cast_if_type(rtype (*)(__VA_ARGS__, void *), (fn), (fn), \
128 rtype (*)(__VA_ARGS__, typeof(arg)))
130 * typesafe_cb_postargs - cast a callback function if it matches the arg
131 * @rtype: the return type of the callback function
132 * @fn: the callback function to cast
133 * @arg: the (pointer) argument to hand to the callback function.
135 * This is a version of typesafe_cb() for callbacks that take other arguments
139 * void _register_callback(void (*fn)(void *arg, int), void *arg);
140 * #define register_callback(fn, arg) \
141 * _register_callback(typesafe_cb_postargs(void, (fn), (arg), int),\
144 #define typesafe_cb_postargs(rtype, fn, arg, ...) \
145 cast_if_type(rtype (*)(void *, __VA_ARGS__), (fn), (fn), \
146 rtype (*)(typeof(arg), __VA_ARGS__))
148 * typesafe_cb_cmp - cast a compare function if it matches the arg
149 * @rtype: the return type of the callback function
150 * @fn: the callback function to cast
151 * @arg: the (pointer) argument(s) to hand to the compare function.
153 * If a callback function takes two matching-type arguments, this macro does
154 * appropriate casts to a function which takes two const void * arguments if
155 * the callback provided takes two a const pointers to @arg.
157 * It is assumed that @arg is of pointer type: usually @arg is passed
158 * or assigned to a void * elsewhere anyway. Note also that the type
159 * arg points to must be defined.
162 * void _my_qsort(void *base, size_t nmemb, size_t size,
163 * int (*cmp)(const void *, const void *));
164 * #define my_qsort(base, nmemb, cmpfn) \
165 * _my_qsort((base), (nmemb), sizeof(*(base)), \
166 * typesafe_cb_cmp(int, (cmpfn), (base)), (arg))
168 #define typesafe_cb_cmp(rtype, cmpfn, arg) \
169 cast_if_type(rtype (*)(const void *, const void *), (cmpfn), \
170 rtype (*)(const typeof(*arg)*, const typeof(*arg)*))
172 #endif /* CCAN_CAST_IF_TYPE_H */