Re: [boost] [review] Outcome Review Report

Subject: Re: [boost] [review] Outcome Review Report
From: Gottlob Frege (gottlobfrege_at_[hidden])
Date: 2017-06-06 15:31:07

Consider also "assume" instead of "accept":

T & t = oc.assume_value();

?

On Tue, Jun 6, 2017 at 11:15 AM, Niall Douglas via Boost
<boost_at_[hidden]> wrote:
>> Since conclusion of the review period, discussion continues (on and
>> off-list) regarding possible evolution to the Outcome library, related to
>> feedback provided during this review, and related to discussions of design
>> evolution for pertinent libraries (e.g., possible changes to
>> std::expected<>, and evolution of a never-empty ‘variant2<>’).  It is
>> promising that such a strong library as Outcome continues to receive
>> critical attention and evolution by multiple interested parties.
>
> Thank you so much Charley for review managing one of the lengthiest and
> most complex reviews we have had here at Boost in some year.
>
> I like to take a month's break from all programming after a review has
> ended, as it happens I have lots of non-programming stuff backlogged
> anyway, so it's good timing. But for those not following the continuing
> discussions, the rough plan moving forward is this:
>
> 1. Expected implementation to be no longer implemented by Outcome, maybe
> by Peter Dimov's Variant2 library at some future point instead.
>
> 2. Outcome to drop the variant based storage. Outcome gets simplified
> into this synopsis (design still evolving, this is a snapshot of current
> thinking):
>
> ```
> template<
>   class T,
>   class EC = error_code_extended
>> class result
> {
>   T _value;
>   EC _error;  // 24 bytes
> public:
>   // Constructors to be inspired by std::variant's
>
>   // Narrow observers
>   T &access_value() noexcept;
>   EC &access_error() noexcept;
>
>   // Wide observers
>   T &value();
>   EC &error();
> };
>
> template<
>   class T,
>   class P = shared_ptr<void>,
>   class EC = error_code_extended,
>   class E = exception_ptr
>>
> class outcome
>   : private result<T, EC>
> {
>   using base = result<T, EC>;
>   union
>   {
>     P _payload;    // 16 bytes
>     E _exception;  //  8 bytes
>   };
> public:
>   // Constructors to be inspired by std::variant's
>
>   // Explicit construction from compatible result<_T, _EC>
>   template<class _T, class _EC> explicit outcome(result<_T, _EC>);
>
>   // Narrow observers
>   using base::access_value;
>   using base::access_error;
>   P &access_payload() noexcept;
>   E &access_exception() noexcept;
>
>   // Wide observers
>   using base::value;
>   using base::error;
>   P payload();
>   E exception();
>   // Returns exception state, but if errored, synthesises
>   // an exception_ptr of the error code
>   E failure();
> };
>
> static_assert(sizeof(outcome<void>) == 40);  // bytes overhead
> ```
>
> I've left out some detail, but the above gives the idea.
>
>> Great thanks to the Boost Community for their tremendous efforts,
>> disciplined review, and detailed exploration of topics in considering this
>> library submission.
>>
>> Sincerest appreciation to Niall Douglas (Author of the Outcome Library) for
>> pushing the envelope for low-latency <error|exception> handling and for
>> submitting his work to the Boost Review process.
>
> Thank you to the Boost community so much for helping me with the design
> of this library. It helps a great deal to return to the drawing board
> armed with so much high quality feedback.
>
> Niall
>
> --
> ned Productions Limited Consulting
> http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/
>
>
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