Re: Mother of all Variants

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-07-04 08:42:05

On 7/4/19 8:00 AM, Robert Ramey via Boost wrote:
> On 7/3/19 12:40 PM, Andrey Semashev via Boost wrote:
>> On 7/3/19 7:42 PM, Robert Ramey via Boost wrote:
>>>
>>> The policy based design is an implement technique to specify the set 
>>> of legitimate variations of a design which the user might need 
>>> without the need to write multiple types.  Right now we have:
>>>
>>> boost::variant
>>> std::variant
>>> boost::variant2
>>> boost::outcome
>>> ?::expected
>>> boost::optional
>>> std::optional
>>> ... ?
>>>
>>> Each one of these is a hodgepodge of design decisions arrived at 
>>> after very, very, very long speculative discussion.  That are really 
>>> all just special cases of the the concept of "typesafe variant".
>>
>> We've already had this discussion, and I'll reiterate that these types 
>> are not merely special cases - they serve their specific purposes and 
>> have interfaces and behavior tailored for their respective uses.
> 
> To me, it's just about code reuse.  The class with the policies contains 
> all the variations for different features.  The aliases just select 
> which features are to be used.

Code can be reused without implementing this meta-variant.