Re: [boost] Exception Visitor

From: Oleg Abrosimov (beholder_at_[hidden])
Date: 2006-07-27 01:03:10

Jeremy Day wrote:
> [snip]
> Now if ExceptionHandler has a nested exceptions type you don't need to do
> something along the lines of
> catcher<my_exceptions>(my_exception_handler()).  However, if you want to
> avoid coupling the exceptions with the handler you can have them separate.
> 
> Here is the full example from General_Catcher.cpp.
> 
> #include "catcher.hpp"
> #include <iostream>
> #include <boost/mpl/vector.hpp>
> 
> [snip]
 >
> int main(int argc, char* argv[])
>     {
>     typedef boost::mpl::vector<std::logic_error, std::exception> exceptions;
> 
>     try
>         {
>         throw(std::logic_error("testing"));
>         } //end of try block
>     catch(...)
>         {
>         catcher<exceptions>(my_exception_handler2());
>         } //end of catch(...) block
> [snip]
>     } //end of int main(int argc, char* argv[])

Hello, Jeremy!

Thank you for your involvement in this topic. I'm very interested in 
pushing it to a complete solution one day.

one further improvement I see is to define simple macros to eliminate 
some details from client code. something like this would be appropriate:

try {
     throw std::logic_error("testing");
} BOOST_CATCH(my_exception_handler());

and

try {
     throw std::logic_error("testing");
} BOOST_CATCH_EX(exceptions, my_exception_handler());

and of course, I agree with David Abrahams that exceptions typelist 
should be sorted to handle most derived first. boost::is_base_of<Base, 
Derived> from type_traits library can be used to achieve it.

One more idea to improve maintainability of client code:

class my_exceptions_handler
{
     BOOST_DEFINE_EXCEPTION_HANDLER_FIRST(exception_type, 
exception_variable, 1)
     {
         //code here
     }
     BOOST_DEFINE_EXCEPTION_HANDLER(exception_type2, exception_variable, 
1, 2)
     {
         //code here
     }
     BOOST_DEFINE_EXCEPTION_HANDLER(exception_type2, exception_variable, 
2, 3)
     {
         //code here
     }
     BOOST_DEFINE_EXCEPTION_HANDLER_LAST(exception_type, 
exception_variable, 3)
     {
         //code here
     }
};

These macros automatically define exceptions list eliminating last piece 
of code duplication. numbers are used to decorate typelist' name that is 
already defined.

Best,
Oleg Abrosimov.