Emil Dotchevski wrote:
On 9/30/07, Tom Brinkman <reportbase@gmail.com> wrote:
3) Support for linking multiple error tags in a single expression might be useful and help in standarizing errors throughout an application.
throw boost:::exception() << boost::error_info<tag_errorno,tag_filename,tag_size,tag_width>( (1,"output.txt",100,200);
Could you clarify what you mean? Well, I could do something like this:
typedef boost::error_info<tag_errorno, tag_filename,tag_size,tag_width> error_t;
throw error_t(1,"output.txt",100,200);
You probably mean:
throw my_error() << error_t(1,"output.txt",100,200);
In my opinion what you're describing is better accomplished like this:
<snip lot's of code> It's not at all obvious why using that much boilerplate is better.
I think it is a mistake to standardize globally on the info you want to stuff into the exception at the time of the throw. What if you detect an error condition that matches the my_error semantics completely, yet you don't have a file name to pass to its constructor? You'd find a way to make the file name available to the throw site, right?
Instead, Boost Exception allows you to just throw my_error(), even though you don't have all info needed to handle it; such info can be added later on, as the exception bubbles up to a context where it is available naturally.
I see. This feature is most valuable. However, so is Tom's suggestion and I don't think both are mutually exclusive (that is if we let go of using the template-id 'error_info' for the latter): typedef boost::custom_exception<tag:: errno,tag::filename,tag::size> file_error; Note custom_exceptions would inherit from boost::exception. We could go further and check the first argument for being an exception type (directly or indirectly derived from boost::exception) to replace that default: typedef boost::custom_exception< an_error , tag::errno,tag::filename,tag::size> file_error; After catching an 'an_error& e' thrown like this throw file_error(errno,name,size); you can still e << boost::error_info<tag::more>(more); Regards, Tobias Schwinger - Review Manager -