On Wed, Oct 28, 2009 at 6:46 PM, Domagoj Saric <dsaritz@gmail.com> wrote:
"Emil Dotchevski" <emildotchevski@gmail.com> wrote in message news:c72e33ce0910281332m5ec6d444gf249609963661587@mail.gmail.com...
On Wed, Oct 28, 2009 at 12:40 PM, Detlef Vollmann <dv@vollmann.ch> wrote:
Domagoj Saric wrote:
~error() ( if ( !inspected ) throw actual_error_; )
This was discussed in the POSIX/C++ meeting 10 days ago, and was considered to be a good idea. Unfortunately, in the current C++ working paper, we have in 17.6.4.10 Restrictions on exception handling [res.on.exception.handling]: "4 Destructor operations defined in the C++ standard library shall not throw exceptions. "
A library should either throw when the error is detected or not. If it doesn't, the user might still throw, but the *library* throwing later seems a very bad idea. Not to mention the issue that throwing in a destructor can end up calling abort().
i mentioned the latter 'issue' already in the first post... generally both points seem to me like non-issues because they cannot become issues unintentionally... both can come into play _only_ if the user converts the temporary return object into a local scoped object/variable...which, as far as i know, you cannot do 'by accident'/unintentionally...you have to be verbose about it...(although, ironically the new auto makes it easier for you to do "the wrong thing"...but still not easy enough that you can do it by a 'non conscious mistake')...
bool diff(file srcA, file srcB, file output) { // get our files ready... error_code srcA_err = file_open(srcA); error_code srcB_err = file_open(srcB); error_code out_err = file_open(output); if (srcA_err || srcB_err || out_err) // check for errors return false; // do the diff... return true; } If srcA_err is true, then srcB_err and out_err aren't checked. On function exit, out_err throws on destruction, srcB_err throws on destruction during stack unwinding. (I think.) So that took a bit of thought for me to come up with, but the code doesn't look completely unreasonable, does it? Basically, you never want more than one actual error_code to exist at a time (per thread). Temporary copies would be OK (should be moveable anyhow, or ref counted). This could be checked for in the debug build. Tony <p.s. hope this doesn't get posted multiple times - gmail wasn't responding, so I'm resending...>