Re: [boost] [outcome] Change semantics on UB from peer review agreed semantics?

czw., 13 wrz 2018 o 09:51 Niall Douglas via Boost napisał(a):

...

*Having said that*, if I'm understanding correctly, this sounds like it would mean that you won't be able to use a custom error_type with Outcome unless you either:

1. Declare some "this is how you throw an exception for this error_type" method (presumably a template specialisation?)

2. Only ever use it with some non-default policy (that either never throws or has user-implemented code to throw).

Is that correct? (Or would #1 always be required regardless of usage?)

Front line `result` would become unusable with UDT E types yes. If people want UDT E types, they would need to use `result`, `unchecked`, or `checked`.

So what's being proposed here is that `result` becomes strictly for E types which are convertible to error code or exception ptr only. Everything else fails to compile with a suggestion "please go use checked or unchecked for UDT E types".

Just for completeness, users will have a yet another option already available today: Specify customization points for your type UDT (funciton make_error_code()) and you can continue using `result` with the default policy (which will throw `system_error`). Regards, &rzej;

...

On the *other* other hand, it wouldn't be a silly idea to have a generic "throw this error_type" method. system_error itself was somewhat trying to be that generic method, but with the caveat of only supporting plain enum error_types.

Perhaps boost::throw_error, which is expected to internally construct an appropriate exception based on its argument type and then call boost::throw_exception?

Me personally I almost exclusively use Outcome in P1028 SG14 `status_code` mode now. Far superior codegen. SG14 `status_code` permits arbitrary error coding types, and can throw arbitrary exceptions from those. Outcome in SG14 `status_code` mode delegates the exception throwing to `status_code`.

I'm fairly sure a major games studio has rolled out SG14 `status_code` into its code. They seem very pleased with it. It does indeed produce very lovely looking assembler.

Niall

_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost