Re: [boost] [review] **NEXT WEEK** Review of Outcome (starts Fri-19-May)

Subject: Re: [boost] [review] **NEXT WEEK** Review of Outcome (starts Fri-19-May)
From: Peter Dimov (lists_at_[hidden])
Date: 2017-05-15 10:37:19

Andrzej Krzemienski вроте:
> vector<outcome<T>> os (20); // no value or error to assign yet
>
> for (auto const& e : some_collection)
> if (cond(e))
>   os[i].set_value();
> else
>   os[i].set_exception();

.set_error presumably. (Incidentally, result<> is documented to have 
set_exception, which makes no sense to me.)

> And in some cases, you cannot immediately rewrite the code in order to 
> avoid default construction. You do not want to return an "empty" object, 
> but you need this value temporarily, end there may be no good value of `E` 
> to use.

The argument that it's better to default-construct to some kind of a 
valueless state instead of T{} is legitimate, but even if I grant all the 
premises of that example (which is a stretch), I still don't see why 
default-constructing to make_error_code( outcome_errc::uninitiaized ) isn't 
better than special-casing the empty state.