Subject: Re: P2320: "The Syntax of Static Reflection" feedback request
From: Roland Bock (rbock_at_[hidden])
Date: 2021-02-17 00:26:43
On 15.02.21 22:25, Hana Dusíková via SG7 wrote:
> Andrew, Wyatt, and Daveed kindly finished the paper which was mentioned
> during last SG7 session and because the next SG7 meeting is next week *I
> would like all of you to read the paper and send feedback to SG7 mailing
> list*, so we have as much of information as possible.
> The paper is here: https://isocpp.org/files/papers/P2320R0.pdf
> <https://isocpp.org/files/papers/P2320R0.pdf> and it will be part of the
> next mailing.
The syntax looks looks good to me in general. But I am easy to please,
as long as I get the functionality :-)
The real concern I have is that examples are (probably by nature) rather
wooden. In the last couple of weeks, I tried to implement std::tuple
without inheritance, as a simple struct with data members, i.e.
// ... some operators
// And then data members that are generated as something like
// This part might require fragments as proposed in P2237R0
I know the current syntax proposal is incomplete, e.g. leaving out
identifier splices, but I would like to urge/challenge you to try
writing such a tuple as a litmus test.
In particular, I would like to draw your attention to
a) the following constructors
constexpr tuple(const Ts&... args);
constexpr tuple(Us&&... args);
template< class... Us>
constexpr tuple(const tuple<Us...>& other);
template <class... Us>
constexpr tuple(tuple<Us...>&& other);
template< class... Tuples >
constexpr std::tuple<CTypes...> tuple_cat(Tuples&&... args);
Both tasks look deceivingly simple. And they /should/ be simple with
reflection in place, IMHO. Give it a try. How would that look like?
If we cannot write std::tuple nicely(!), I would claim we are doing it
Just my 2ct.
PS: As of today, I have an ugly version of tuple_cat but cannot seem to
figure out how to write those constructors.
PPS: Most other stuff is actually quite elegant.
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