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: Peter Dimov (pdimov_at_[hidden])
Date: 2019-04-02 14:44:28

Andrey Semashev wrote:
> >> 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.

It is a different component. That wasn't the question though. The question 
was, why not have it as a separate library. And the answer is, because the 
two components share too much of an implementation, and because the design 
decisions made about one component affect the other (and vice versa - the 
converting constructor and the subset() member function of `variant` are 
needed by `expected`).