[strongswan] strongswan METHOD宏

使用METHOD宏的函数定义：

METHOD(message_t, get_message_id, uint32_t,
        private_message_t *this)
{
        return this->message_id;
}     

METHOD宏的定义：

/**
 * Method declaration/definition macro, providing private and public interface.
 *
 * Defines a method name with this as first parameter and a return value ret,
 * and an alias for this method with a _ prefix, having the this argument
 * safely casted to the public interface iface.
 * _name is provided a function pointer, but will get optimized out by GCC.
 */
#define METHOD(iface, name, ret, this, ...) \
        static ret name(union {iface *_public; this;} \
        __attribute__((transparent_union)), ##__VA_ARGS__); \
        static typeof(name) *_##name = (typeof(name)*)name; \
        static ret name(this, ##__VA_ARGS__)  

将METHOD宏展开后的定义：

static uint32_t get_message_id(union {message_t *_public; private_message_t *this;} __attribute__((transparent_union)));
static typeof(get_message_id)* _get_message_id = (typeof(get_message_id)*)get_message_id;
static uint32_t get_message_id(private_message_t *this)  

关于transparent_union的定义：

http://nanjingabcdefg.is-programmer.com/categories/5966/posts