Re: New JSON library from the maker of Beast!

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2019-10-22 22:00:58

On Tue, Oct 22, 2019 at 2:53 PM Gavin Lambert via Boost <
boost_at_[hidden]> wrote:

> On 23/10/2019 05:25, Vinnie Falco wrote:
> >> So I'm curious why it should be different here. Does the doc goes into
> that already?
> >
> > `json::value` is not `variant<...>` for the same reason that
> > `string_view` is not `std::pair<char const*, std::size_t>`.
>
> That's a good reason for not inheriting from it.
>
> It's not a good reason for not using it as a private member, to avoid
> reimplementing the variant-storage concept.
> (Though there may be other good reasons for that.)
>

There are always two kinds of dependencies, logical and physical.
Logically, you use something as a private member, you're ok, but physically
you're still dependent on it, and that may be a problem. Further,
std::variant may be problematic for portability, and it may or may not be
as efficient as something hand-written specifically for the purpose.
Consider that if performance is critical, you don't want to deal with "I
changed my compiler and now your JSON parser runs 2x slower".