Re: [boost] Boost and exceptions

23 Jun 2012


      On 23/06/2012 18:25, Robert Ramey wrote:
...
Steven Watanabe wrote:
...
Actually, inheriting from boost::exception doesn't
work for this.  To enable copying you have to throw
using boost::enable_current_exception.
...
try {
  throw enable_current_exception(x);
} catch(...) {
  exception_ptr e = current_exception();
}
// move e to another thread
rethrow_exception(e);
OK - get it - but I don't see that it adds any value compared to
try {
     throw x;
}
catch(...){
     exception_ptr e = std::current_exception();
     std::rethrow_exception(e); //  n3242 18.8}
}
Would you happen to know which compilers implement n3242 already? 
Boost.Exception works for me with the compilers I use everyday, as long 
as the original exception was thrown with enable_current_exception.
...
...
The code using Boost.Exception would look like:
...
typedef boost::error_info<
  struct tag_archive_filename, std::string> archive_filename;
...
try {
  ifstream is(filename);
  binary_archive ia(is);
  my_data d;
  ia >> d;
} catch (boost::exception& e) {
  e << archive_filename(filename);
  throw;
}
lol - now you've thrown away all the information in archive_exception!
Use this instead.
Most certainly not, the **type** of the original exception is not lost 
when using boost::throw_exception. In this case, e is still an 
archive_exception.
...
...
...
If you really like
boost::exception
your code when you eventually can eventually rethrow
catch (std::exception e){
     BOOST_EXCEPTION_THROW_EXCEPTION(e)
}
This of course loses the original type of the exception.
I don't think that's true. It's not clear to me from the documentation.
I get this idea from looking at the code.  Of course if it
were true it would be huge blunder in the design of the library.
Wouldn't that just throw a sliced copy of the exception, a new exception 
of type std::exception, instead of rethrowing the original exception?

Agustín K-ballo Bergé.-