Boost logo

Boost :

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2006-11-10 14:18:06

Oliver.Kowalke_at_[hidden] wrote:
>> throw my_exception() <<
>> throw_info<tag_errno>(errno) <<
>> throw_info<tag_function>(BOOST_CURRENT_FUNCTION);
>> <snip>
>> Any strong preferences?
> What about upcoming boost::system::error_code and
> boost::system::system_error (used to report os errors)?

My example (above) was derived from,
and it was only intended to visualize what that example would look like if
exception_info is renamed to throw_info due to the name clash with the
exception_info macro defined in windows.h (but see Minh's responce in which
he proposes the name error_info, which I think is what I'm going with now.)

If I read you correctly, what you're saying is that if boost::exception is
accepted, we need to think about integration with the rest of boost. For
example, if boost::system::system_error derives from std::runtime_error (as
it does now) and also from boost::exception, (someone correct me if I'm
missing something) the definition of boost::system_error could be reduced

struct tag_system_error_code: exception_info_value<error_code> { };
struct tag_sytem_error_msg: exception_info_value<std::string> { };
struct tag_system_error_action: exception_info_value<message_action> { };
struct tag_system_error_category: exception_info_value<error_category> { };

class system_error:
    public std::runtime_error,
    public boost::exception
    char const * what() const throw() //resolve ambiguity.
        return boost::exception::what();

Then, when throwing, we can write:

throw system_error() <<
    exception_info<tag_system_error_code>(ec) <<
    exception_info<tag_system_error_msg>(msg) <<
    ... ;

depending on what information is available to us. This also allows contexts
that are higher in the call stack to catch( boost::exception & ), encode
additional information available to them and rethrow. The rationale for this
is discussed here:

It is also possible to keep the current definition of class system_error,
and simply change throw statements to:

throw enable_exception_info(system_error(....));

This also enables contexts that are higher in the call stack to catch(
boost::exception & ), add more values and rethrow, without interfering with
code unaware of boost::exception.

--Emil Dotchevski

Boost list run by bdawes at, gregod at, cpdaniel at, john at