Re: Mother of all Variants

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-07-03 12:41:07

On 7/3/19 3:36 PM, Emil Dotchevski via Boost wrote:
> On Tue, Jul 2, 2019 at 7:19 PM Nevin Liber via Boost <boost_at_[hidden]>
> wrote:
>>
>> On Thu, Jun 27, 2019 at 7:41 PM Robert Ramey via Boost <
>> boost_at_[hidden]> wrote:
>>
>>> Here you've exactly hit on the motivation for mother of all variants.
>>>
>>> It should be clear by now that as library developers we cannot correctly
>>> anticipate the needs and desires of our potential users and at the same
>>> time document the rational and restrictions of the particular variant in
>>> question.
>>
>>
>> That is true about every type in existence.  Variant is not special in
> this
>> regard.
>>
>> And if "we cannot correctly anticipate the needs and desires of our
>> potential users", policies also "cannot correctly
>> anticipate the needs and desires of our potential users" either.  Policies
>> do not solve this problem.
> 
> +1
> 
> Worse, policy-based designs are the result of the expert in the problem
> domain (the library author), unable to make up his mind about the library
> design, pushing that responsibility to people who are less knowledgeable
> (the library users).

I wouldn't put it that far. A policy can be useful when there are 
legitimate use cases for multiple behaviors in some aspect for the 
otherwise same component.