lib/ccan/typesafe_cb/typesafe_cb.h

   1 /* Licensed under LGPLv2.1+ - see LICENSE file for details */
   2 #ifndef CCAN_TYPESAFE_CB_H
   3 #define CCAN_TYPESAFE_CB_H
   4 #include "config.h"
   5
   6 #if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
   7 /**
   8  * typesafe_cb_cast - only cast an expression if it matches a given type
   9  * @desttype: the type to cast to
  10  * @oktype: the type we allow
  11  * @expr: the expression to cast
  12  *
  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 is exactly of type @oktype, then it will be
  16  * cast to @desttype type, otherwise left alone.
  17  *
  18  * This macro can be used in static initializers.
  19  *
  20  * This is merely useful for warnings: if the compiler does not
  21  * support the primitives required for typesafe_cb_cast(), it becomes an
  22  * unconditional cast, and the @oktype argument is not used.  In
  23  * particular, this means that @oktype can be a type which uses the
  24  * "typeof": it will not be evaluated if typeof is not supported.
  25  *
  26  * Example:
  27  *      // We can take either an unsigned long or a void *.
  28  *      void _set_some_value(void *val);
  29  *      #define set_some_value(e)                       \
  30  *              _set_some_value(typesafe_cb_cast(void *, (e), unsigned long))
  31  */
  32 #define typesafe_cb_cast(desttype, oktype, expr)                        \
  33         __builtin_choose_expr(                                          \
  34                 __builtin_types_compatible_p(__typeof__(0?(expr):(expr)), \
  35                                              oktype),                   \
  36                 (desttype)(expr), (expr))
  37 #else
  38 #define typesafe_cb_cast(desttype, oktype, expr) ((desttype)(expr))
  39 #endif
  40
  41 /**
  42  * typesafe_cb_cast3 - only cast an expression if it matches given types
  43  * @desttype: the type to cast to
  44  * @ok1: the first type we allow
  45  * @ok2: the second type we allow
  46  * @ok3: the third type we allow
  47  * @expr: the expression to cast
  48  *
  49  * This is a convenient wrapper for multiple typesafe_cb_cast() calls.
  50  * You can chain them inside each other (ie. use typesafe_cb_cast()
  51  * for expr) if you need more than 3 arguments.
  52  *
  53  * Example:
  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(typesafe_cb_cast3(void *,,              \
  58  *                                          long, unsigned long, const void *,\
  59  *                                          (expr)))
  60  */
  61 #define typesafe_cb_cast3(desttype, ok1, ok2, ok3, expr)                \
  62         typesafe_cb_cast(desttype, ok1,                                 \
  63                          typesafe_cb_cast(desttype, ok2,                \
  64                                           typesafe_cb_cast(desttype, ok3, \
  65                                                            (expr))))
  66
  67 /**
  68  * typesafe_cb - cast a callback function if it matches the arg
  69  * @rtype: the return type of the callback function
  70  * @atype: the (pointer) type which the callback function expects.
  71  * @fn: the callback function to cast
  72  * @arg: the (pointer) argument to hand to the callback function.
  73  *
  74  * If a callback function takes a single argument, this macro does
  75  * appropriate casts to a function which takes a single atype argument if the
  76  * callback provided matches the @arg.
  77  *
  78  * It is assumed that @arg is of pointer type: usually @arg is passed
  79  * or assigned to a void * elsewhere anyway.
  80  *
  81  * Example:
  82  *      void _register_callback(void (*fn)(void *arg), void *arg);
  83  *      #define register_callback(fn, arg) \
  84  *              _register_callback(typesafe_cb(void, (fn), void*, (arg)), (arg))
  85  */
  86 #define typesafe_cb(rtype, atype, fn, arg)                      \
  87         typesafe_cb_cast(rtype (*)(atype),                      \
  88                          rtype (*)(__typeof__(arg)),            \
  89                          (fn))
  90
  91 /**
  92  * typesafe_cb_preargs - cast a callback function if it matches the arg
  93  * @rtype: the return type of the callback function
  94  * @atype: the (pointer) type which the callback function expects.
  95  * @fn: the callback function to cast
  96  * @arg: the (pointer) argument to hand to the callback function.
  97  *
  98  * This is a version of typesafe_cb() for callbacks that take other arguments
  99  * before the @arg.
 100  *
 101  * Example:
 102  *      void _register_callback(void (*fn)(int, void *arg), void *arg);
 103  *      #define register_callback(fn, arg)                                 \
 104  *              _register_callback(typesafe_cb_preargs(void, void *,       \
 105  *                                 (fn), (arg), int),                      \
 106  *                                 (arg))
 107  */
 108 #define typesafe_cb_preargs(rtype, atype, fn, arg, ...)                 \
 109         typesafe_cb_cast(rtype (*)(__VA_ARGS__, atype),                 \
 110                          rtype (*)(__VA_ARGS__, __typeof__(arg)),       \
 111                          (fn))
 112
 113 /**
 114  * typesafe_cb_postargs - cast a callback function if it matches the arg
 115  * @rtype: the return type of the callback function
 116  * @atype: the (pointer) type which the callback function expects.
 117  * @fn: the callback function to cast
 118  * @arg: the (pointer) argument to hand to the callback function.
 119  *
 120  * This is a version of typesafe_cb() for callbacks that take other arguments
 121  * after the @arg.
 122  *
 123  * Example:
 124  *      void _register_callback(void (*fn)(void *arg, int), void *arg);
 125  *      #define register_callback(fn, arg) \
 126  *              _register_callback(typesafe_cb_postargs(void, (fn), void *, \
 127  *                                 (arg), int),                             \
 128  *                                 (arg))
 129  */
 130 #define typesafe_cb_postargs(rtype, atype, fn, arg, ...)                \
 131         typesafe_cb_cast(rtype (*)(atype, __VA_ARGS__),                 \
 132                          rtype (*)(__typeof__(arg), __VA_ARGS__),       \
 133                          (fn))
 134 #endif /* CCAN_CAST_IF_TYPE_H */