Re: Diagnostic improvements in 1.78/1.79

From: Gavin Lambert (boost_at_[hidden])
Date: 2022-02-15 03:18:22

On 15/02/2022 15:38, Peter Dimov wrote:
> I think there might be a misunderstanding here. What I envisage is this
> 
> void (*throw_handler)( std::exception const& ex, boost::exception& bx,
>    boost::source_location const* loc ) = default_throw_handler;
> 
> void set_throw_handler( auto* p ) { throw_handler = p; }
[...]

My point is that only the final end-user can call set_throw_handler 
(unless perhaps you make it a registration chain instead, and invoke all 
of the callbacks -- which after adding RAII makes it resemble the 
context objects I mentioned previously), which makes it harder to tack 
on additional information from a library context (or in passing rather 
than having to catch and rethrow).

But that's also a bit different from what I was envisaging -- why is it 
that you've modified the callback signature to carry the source_location 
across?  Wouldn't this be better:

     void (*throw_handler)( std::exception const& ex, boost::exception& 
bx ) = default_throw_handler;

     void set_throw_handler( auto* p ) { throw_handler = p; }

     void default_throw_handler( std::exception const& ex, 
boost::exception& bx )
     {
     }

     template<class E> BOOST_NORETURN void throw_exception( E const & e )
     {
         wrapexcept<E> wx( e );
         throw_handler( e, wx );
         throw wx;
     }

     template<class E> BOOST_NORETURN void throw_exception( E const & e,
       boost::source_location const & loc )
     {
         wrapexcept<E> wx( e );
         wx.set_location( loc );
         throw_handler( e, wx );
         throw wx;
     }

(Or perhaps only passing the boost::exception to the handler; I'm not 
sure why it would need both.)

This means the source_location is just like any other data you want to 
attach; it doesn't get special treatment.