Subject: Re: [boost] [outcome] expected vs. result
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-24 14:44:53
> I am trying to summarize differences between `expected<T, error_code>` and
> `result<T>`. So far, I have identified the following:
Sorry I didn't answer this earlier. I've been trying to reply to the
short emails and bug reports early and deal with the longer replies on a
first received first replied basis. I missed this one.
> 1. API/ABI stability guarantees.
> 2. `result` has empty state - `expected` does not.
*Formal* empty state. Yes.
> 3. `result` uses error_code_extended for more error details in the
result and outcome hard code E to error_code_extended. expected defaults
E to error_code. You can, of course, manually supply error_code_extended
as E to expected.
> 4. No ordering (operator<) for `result`
No, nothing gets ordering operators. It is unsafe to combine ordering
operators with implicit conversion according to your own blog!
> Is the above list complete?
No, result has a wide contract on all its member functions such that you
can never achieve undefined behaviour. That's those woolly "default
actions" previously discussed.
expected implements operator*, operator->, .error() etc as reinterpret_cast.
-- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk