Re: [boost] [variant2] Review of Variant2 started today : April 1 - April 10

Subject: Re: [boost] [variant2] Review of Variant2 started today : April 1 - April 10
From: Robert Ramey (ramey_at_[hidden])
Date: 2019-04-02 14:38:14

On 4/2/19 7:31 AM, Andrey Semashev via Boost wrote:
> On 4/2/19 4:18 PM, Peter Dimov via Boost wrote:
>> Andrey Semashev wrote:
>>> On 4/2/19 3:55 PM, Peter Dimov via Boost wrote:
>>> > Michael Caisse wrote:
>>> >
>>> >> Note: The repository contains an expected implementation also; 
>>> however, >> that is not being considered in this review.
>>> >
>>> > To be clear, I do intend to finish `expected` and provide it as 
>>> part of > the library.
>>>
>>> Will it be reviewed separately?
>>
>> No. If you don't like it, now is the time to reject.
> 
> In that case, `expected` should be part of this review and contribute to 
> the final decision.
> 
>>> Also, IMHO, it's better to have libraries more focused and fine 
>>> grained. Why not have `expected` as a separate library?
>>
>> expected<T, E...> is basically a variant, with a slightly different 
>> interface.
> 
> It might be implemented like/with variant, but conceptually this is a 
> different component. Just like `optional` is a different component than 
> `variant`. All these components have different use cases and communicate 
> different intentions.

Personally, I've always found that characterizing option, expected, et. 
all as different/unique components is a bad idea.  I much prefer a 
single simple idea - a variant as a simple sum of other types - while 
the others are more specific "variations" of the fundamental type.  It's 
less redundant, easier to reason about, easier to remember, and less 
work to document.  There is also a natural C++ implementation in terms 
of inheritance.

Robert Ramey
> 
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