1 files changed, 133 insertions, 0 deletions
diff --git a/lib/ccan/typesafe_cb/typesafe_cb.h b/lib/ccan/typesafe_cb/typesafe_cb.h
new file mode 100644
index 00000000000..40cfa397989
--- /dev/null
+++ b/lib/ccan/typesafe_cb/typesafe_cb.h
@@ -0,0 +1,133 @@
+#ifndef CCAN_TYPESAFE_CB_H
+#define CCAN_TYPESAFE_CB_H
+#include "config.h"
+
+#if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
+/**
+ * typesafe_cb_cast - only cast an expression if it matches a given type
+ * @desttype: the type to cast to
+ * @oktype: the type we allow
+ * @expr: the expression to cast
+ *
+ * This macro is used to create functions which allow multiple types.
+ * The result of this macro is used somewhere that a @desttype type is
+ * expected: if @expr is exactly of type @oktype, then it will be
+ * cast to @desttype type, otherwise left alone.
+ *
+ * This macro can be used in static initializers.
+ *
+ * This is merely useful for warnings: if the compiler does not
+ * support the primitives required for typesafe_cb_cast(), it becomes an
+ * unconditional cast, and the @oktype argument is not used.  In
+ * particular, this means that @oktype can be a type which uses the
+ * "typeof": it will not be evaluated if typeof is not supported.
+ *
+ * Example:
+ *	// We can take either an unsigned long or a void *.
+ *	void _set_some_value(void *val);
+ *	#define set_some_value(e)			\
+ *		_set_some_value(typesafe_cb_cast(void *, (e), unsigned long))
+ */
+#define typesafe_cb_cast(desttype, oktype, expr)			\
+	__builtin_choose_expr(						\
+		__builtin_types_compatible_p(__typeof__(0?(expr):(expr)), \
+					     oktype),			\
+		(desttype)(expr), (expr))
+#else
+#define typesafe_cb_cast(desttype, oktype, expr) ((desttype)(expr))
+#endif
+
+/**
+ * typesafe_cb_cast3 - only cast an expression if it matches given types
+ * @desttype: the type to cast to
+ * @ok1: the first type we allow
+ * @ok2: the second type we allow
+ * @ok3: the third type we allow
+ * @expr: the expression to cast
+ *
+ * This is a convenient wrapper for multiple typesafe_cb_cast() calls.
+ * You can chain them inside each other (ie. use typesafe_cb_cast()
+ * for expr) if you need more than 3 arguments.
+ *
+ * Example:
+ *	// We can take either a long, unsigned long, void * or a const void *.
+ *	void _set_some_value(void *val);
+ *	#define set_some_value(expr)					\
+ *		_set_some_value(typesafe_cb_cast3(void *,,		\
+ *					    long, unsigned long, const void *,\
+ *					    (expr)))
+ */
+#define typesafe_cb_cast3(desttype, ok1, ok2, ok3, expr)		\
+	typesafe_cb_cast(desttype, ok1,					\
+			 typesafe_cb_cast(desttype, ok2,		\
+					  typesafe_cb_cast(desttype, ok3, \
+							   (expr))))
+
+/**
+ * typesafe_cb - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @atype: the (pointer) type which the callback function expects.
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * If a callback function takes a single argument, this macro does
+ * appropriate casts to a function which takes a single atype argument if the
+ * callback provided matches the @arg.
+ *
+ * It is assumed that @arg is of pointer type: usually @arg is passed
+ * or assigned to a void * elsewhere anyway.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(void *arg), void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb(void, (fn), void*, (arg)), (arg))
+ */
+#define typesafe_cb(rtype, atype, fn, arg)			\
+	typesafe_cb_cast(rtype (*)(atype),			\
+			 rtype (*)(__typeof__(arg)),		\
+			 (fn))
+
+/**
+ * typesafe_cb_preargs - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @atype: the (pointer) type which the callback function expects.
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * This is a version of typesafe_cb() for callbacks that take other arguments
+ * before the @arg.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(int, void *arg), void *arg);
+ *	#define register_callback(fn, arg)				   \
+ *		_register_callback(typesafe_cb_preargs(void, (fn), void *, \
+ *				   (arg), int),				   \
+ *				   (arg))
+ */
+#define typesafe_cb_preargs(rtype, atype, fn, arg, ...)			\
+	typesafe_cb_cast(rtype (*)(__VA_ARGS__, atype),			\
+			 rtype (*)(__VA_ARGS__, __typeof__(arg)),	\
+			 (fn))
+
+/**
+ * typesafe_cb_postargs - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @atype: the (pointer) type which the callback function expects.
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * This is a version of typesafe_cb() for callbacks that take other arguments
+ * after the @arg.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(void *arg, int), void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb_postargs(void, (fn), void *, \
+ *				   (arg), int),				    \
+ *				   (arg))
+ */
+#define typesafe_cb_postargs(rtype, atype, fn, arg, ...)		\
+	typesafe_cb_cast(rtype (*)(atype, __VA_ARGS__),			\
+			 rtype (*)(__typeof__(arg), __VA_ARGS__),	\
+			 (fn))
+#endif /* CCAN_CAST_IF_TYPE_H */