Re: [boost] [outcome] success-or-failure objects

Subject: Re: [boost] [outcome] success-or-failure objects
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2018-01-26 01:14:04

On 25/01/2018 21:32, Niall Douglas wrote:
> Not to nitpick, but as
> https://ned14.github.io/outcome/tutorial/default-actions/happens1/#fn:1
> describes, calling .error() when there is no error there results in
> *hard* UB. As in, the compiler doesn't generate code to handle the
> situation where there is no error, no branches, no stack handling, nothing.
> 
> The consequence of that *might* be to proceed as if there is no error,
> but sometimes it is not. The Tutorial gives an example of where it
> segfaults. You can't really say, depends on what the optimiser generates
> for some given situation.
> 
> Now, in terms of storage, yes we do always place default initialised E
> in there. That's for the C compatibility. But we don't place a default
> initialised T there, that can be random bits, so .value() where there is
> no value can yield the same random input as you mentioned Outcome v1 had.

Sure.  I didn't mean to imply that just because some UB *might* be 
relatively benign that you should ever intentionally allow it to happen. 
  We're talking about logic errors, where the call was made unintentionally.