AMDG On 06/25/2012 09:37 AM, Robert Ramey wrote:
Emil Dotchevski wrote:
On Sun, Jun 24, 2012 at 11:33 PM, Robert Ramey <ramey@rrsd.com> wrote: <snipped code>
First, as you point out, your code can't be deployed even if it was correct, because many compilers don't yet implement std::exception_ptr.
There a couple of possible answers here, but the simplest would be just to say that you'd need to implement the standard functions for this compiler. I cursory look at the microsoft documentation suggests that this would be possible. and not all that difficult.
Secondly, your program erases the type of the exception object. In C++, the type of the exception and not its value corresponds to its semantics.
hmmm looks to me that my program is not losing the type.
That's not what Emil said. "erases the type" means that it hides everything behind a single static type and forces you to dynamic cast to find the real type. I really don't want to read or write code that looks like this, and I don't think that the problem can be solved without adding something to the original throw site. The problems become even worse when you have more than one independent implementation of this kind of handling, which don't know about each other: void handle_my_exception(my_exception&); void handle_exception_wrapper1(exception_wrapper_base1& e) { try { std::rethrow_exception(e.me); } catch(my_exception& me) { handle_my_exception(me); } catch(exception_wrapper_base2& e2) { handle_exception_wrapper2(e2); } catch(...) { handle_unknown_exception(); } } void handle_exception_wrapper2(exception_wrapper_base2& e) { try { std::rethrow_exception(e.me); } catch(my_exception& me) { handle_my_exception(me); } catch(exception_wrapper_base1& e1) { handle_exception_wrapper1(e1); } catch(...) { handle_unknown_exception(); } } try { // Lots of stuff } catch(my_exception& e) { handle_my_exception(e); } catch(exception_wrapper_base1& e) { handle_exception_wrapper1(e); } catch(exception_wrapper_base2& e) { handle_exception_wrapper2(e); } I don't even want to think about what you need to do if you want to let anything that isn't my_exception go by unchanged. I think that you've gotten so fixated on avoiding instrumenting the original throw site, that it's blinding to the readability issues with your solutions.
The highest level catch does catch the original type and just to be sure I used typeid to print the type restored at this level. So the program output is
$ ./test_misc caught other exception # display original exception type caught exception_wrapper_base caught my_exception # display exception type at highest level 999 # display attached information.
In Christ, Steven Watanabe