lib/ccan/typesafe_cb/typesafe_cb.h

   1 #ifndef CCAN_TYPESAFE_CB_H
   2 #define CCAN_TYPESAFE_CB_H
   3 #include "config.h"
   4
   5 #if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
   6 /**
   7  * typesafe_cb_cast - only cast an expression if it matches a given type
   8  * @desttype: the type to cast to
   9  * @oktype: the type we allow
  10  * @expr: the expression to cast
  11  *
  12  * This macro is used to create functions which allow multiple types.
  13  * The result of this macro is used somewhere that a @desttype type is
  14  * expected: if @expr is exactly of type @oktype, then it will be
  15  * cast to @desttype type, otherwise left alone.
  16  *
  17  * This macro can be used in static initializers.
  18  *
  19  * This is merely useful for warnings: if the compiler does not
  20  * support the primitives required for typesafe_cb_cast(), it becomes an
  21  * unconditional cast, and the @oktype argument is not used.  In
  22  * particular, this means that @oktype can be a type which uses the
  23  * "typeof": it will not be evaluated if typeof is not supported.
  24  *
  25  * Example:
  26  *      // We can take either an unsigned long or a void *.
  27  *      void _set_some_value(void *val);
  28  *      #define set_some_value(e)                       \
  29  *              _set_some_value(typesafe_cb_cast(void *, (e), unsigned long))
  30  */
  31 #define typesafe_cb_cast(desttype, oktype, expr)                        \
  32         __builtin_choose_expr(                                          \
  33                 __builtin_types_compatible_p(__typeof__(0?(expr):(expr)), \
  34                                              oktype),                   \
  35                 (desttype)(expr), (expr))
  36 #else
  37 #define typesafe_cb_cast(desttype, oktype, expr) ((desttype)(expr))
  38 #endif
  39
  40 /**
  41  * typesafe_cb_cast3 - only cast an expression if it matches given types
  42  * @desttype: the type to cast to
  43  * @ok1: the first type we allow
  44  * @ok2: the second type we allow
  45  * @ok3: the third type we allow
  46  * @expr: the expression to cast
  47  *
  48  * This is a convenient wrapper for multiple typesafe_cb_cast() calls.
  49  * You can chain them inside each other (ie. use typesafe_cb_cast()
  50  * for expr) if you need more than 3 arguments.
  51  *
  52  * Example:
  53  *      // We can take either a long, unsigned long, void * or a const void *.
  54  *      void _set_some_value(void *val);
  55  *      #define set_some_value(expr)                                    \
  56  *              _set_some_value(typesafe_cb_cast3(void *,,              \
  57  *                                          long, unsigned long, const void *,\
  58  *                                          (expr)))
  59  */
  60 #define typesafe_cb_cast3(desttype, ok1, ok2, ok3, expr)                \
  61         typesafe_cb_cast(desttype, ok1,                                 \
  62                          typesafe_cb_cast(desttype, ok2,                \
  63                                           typesafe_cb_cast(desttype, ok3, \
  64                                                            (expr))))
  65
  66 /**
  67  * typesafe_cb - cast a callback function if it matches the arg
  68  * @rtype: the return type of the callback function
  69  * @atype: the (pointer) type which the callback function expects.
  70  * @fn: the callback function to cast
  71  * @arg: the (pointer) argument to hand to the callback function.
  72  *
  73  * If a callback function takes a single argument, this macro does
  74  * appropriate casts to a function which takes a single atype argument if the
  75  * callback provided matches the @arg.
  76  *
  77  * It is assumed that @arg is of pointer type: usually @arg is passed
  78  * or assigned to a void * elsewhere anyway.
  79  *
  80  * Example:
  81  *      void _register_callback(void (*fn)(void *arg), void *arg);
  82  *      #define register_callback(fn, arg) \
  83  *              _register_callback(typesafe_cb(void, (fn), void*, (arg)), (arg))
  84  */
  85 #define typesafe_cb(rtype, atype, fn, arg)                      \
  86         typesafe_cb_cast(rtype (*)(atype),                      \
  87                          rtype (*)(__typeof__(arg)),            \
  88                          (fn))
  89
  90 /**
  91  * typesafe_cb_preargs - cast a callback function if it matches the arg
  92  * @rtype: the return type of the callback function
  93  * @atype: the (pointer) type which the callback function expects.
  94  * @fn: the callback function to cast
  95  * @arg: the (pointer) argument to hand to the callback function.
  96  *
  97  * This is a version of typesafe_cb() for callbacks that take other arguments
  98  * before the @arg.
  99  *
 100  * Example:
 101  *      void _register_callback(void (*fn)(int, void *arg), void *arg);
 102  *      #define register_callback(fn, arg)                                 \
 103  *              _register_callback(typesafe_cb_preargs(void, (fn), void *, \
 104  *                                 (arg), int),                            \
 105  *                                 (arg))
 106  */
 107 #define typesafe_cb_preargs(rtype, atype, fn, arg, ...)                 \
 108         typesafe_cb_cast(rtype (*)(__VA_ARGS__, atype),                 \
 109                          rtype (*)(__VA_ARGS__, __typeof__(arg)),       \
 110                          (fn))
 111
 112 /**
 113  * typesafe_cb_postargs - cast a callback function if it matches the arg
 114  * @rtype: the return type of the callback function
 115  * @atype: the (pointer) type which the callback function expects.
 116  * @fn: the callback function to cast
 117  * @arg: the (pointer) argument to hand to the callback function.
 118  *
 119  * This is a version of typesafe_cb() for callbacks that take other arguments
 120  * after the @arg.
 121  *
 122  * Example:
 123  *      void _register_callback(void (*fn)(void *arg, int), void *arg);
 124  *      #define register_callback(fn, arg) \
 125  *              _register_callback(typesafe_cb_postargs(void, (fn), void *, \
 126  *                                 (arg), int),                             \
 127  *                                 (arg))
 128  */
 129 #define typesafe_cb_postargs(rtype, atype, fn, arg, ...)                \
 130         typesafe_cb_cast(rtype (*)(atype, __VA_ARGS__),                 \
 131                          rtype (*)(__typeof__(arg), __VA_ARGS__),       \
 132                          (fn))
 133 #endif /* CCAN_CAST_IF_TYPE_H */