The exceptions will be caught in the order of the items in the exception handler's nested type argument. So in the example catcher tries std::logic_error first, and if the exception isn't of that type it tries std::exception. If the exception isn't of that type it defaults to operator()(void). So basically you take the order of the catch block (top to bottom) and "rotate" it so that the exception types appear in the list from left to right. Jeremy On 7/18/06, Emil Dotchevski <emildotchevski@hotmail.com> wrote:
You seem to be replacing the sequence of catch-es (which is order-specific), with overloading (which isn't). The order is important, because in a way each catch is a more generic fallback for the previous ones.
--Emil
Jeremy Day wrote:
All,
A message a few days ago, along with my current reading of the book 'C++ Template Metaprogramming', piqued my interest in the idea of an "exception visitor". I put together a little something, and I'm wondering if people might be interested in my (rather poor, at the moment) code.
Problem:
When using exceptions it is very easy to end up with code that looks something like this:
try { //Some code that might throw exceptions. } catch(std::logic_error&) { //Handle the exception. } catch(std::exception&) { //Handle exception. } catch(...) { //Handle everything else }
With my code you can transform the above into something along these lines:
struct my_exception_handler { typedef boost::mpl::vector<std::logic_error, std::exception> exceptions;
void operator()(std::exception& oError) { std::cout << "my_exception_handler::operator()(std::exception&)" << std::endl; }
void operator()(std::logic_error& oError) { std::cout << "my_exception_handler::operator()(std::logic_error&)" << std::endl; }
void operator()(void) { std::cout << "my_exception_handler::operator()(void)" << std::endl; } };
//Application code.
try { //Some code that might throw exceptions, such as: throw std::logic_error("A sample logic error."); } catch(...) { //Magic happens here. catcher(my_exception_handler()); //This prints out "my_exception_handler::operator()(std::logic_error&)" }
If anyone is interested I will post what I have for critique (I'm a relative newbie with MPL, so I will likely need a lot of help). I look forward to any and all comments.
Jeremy _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
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