Re: [boost] Exception Visitor

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2006-07-18 13:42:10

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
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