Re: [LEAF] A sort of review

From: Peter Dimov (pdimov_at_[hidden])
Date: 2020-06-04 22:10:20

Emil Dotchevski wrote:

> I remember when Boost Exception was discussed (ancient history now), David 
> Abrahams pointed out that it is unfortunate that it requires an exception 
> to be caught before it can be augmented. In terms of Boost Exception, you 
> must say:
>
> try
> {
>   f();
> }
> catch( boost::exception & e )
> {
>   e << more_info{};
>   throw;
> }
>
> He thought that we're not really doing error handling here, so the 
> addition of more_info should happen automatically. Unfortunately there is 
> no good way to do this with Boost Exception. In that design, you need to 
> interact with the exception object and the only way to get a reference to 
> it is to catch it.

I kind of suspect it will be possible. We could preload the more_info{}, 
a-la LEAF, and then move that into the active exception "record" on 
destruction, if that record is kept outside the exception object, but in a 
side storage like a thread-local map.

Sort of a LEAF/Boost.Exception hybrid, where the boost::exception base only 
contains the error_id like in LEAF, and the actual error_info is in the map.

The `preload` will need to allocate, but the destructor won't, which seems 
enough for our purposes.