Re: [v3 PATCH] Implement N4387 and LWG 2367

[Ville Voutilainen <ville.voutilainen@gmail.com>]

On 7 June 2015 at 09:53, Marc Glisse <marc.glisse@inria.fr> wrote:
> Since the paper does not mention looking at _MoveConstructibleTuple or
> _ImplicitlyMoveConvertibleTuple here, could you add a comment explaining
> why that is needed?

Sure.

> Does the following code still compile with your patch?
> struct A { int a,b; };
> std::tuple<int,int,A> a(3,4,{1,2});

No. :/ And we have no test for it.. I'll need to look at that.

> IMO the parts with is_default_constructible point to a core issue, we should
> not have to duplicate information, especially in such a convoluted way. But
> I guess that has lower priority than noexcept(auto), and I haven't yet
> looked if concepts will help.

Concepts would help a lot, but being able to use them in a library
implementation
is some ways off.

> You use a lot: typename enable_if<X, bool>::type=true
> while the current code seems to favor: class=typename enable_if<X>::type.
> I don't really care which one is used, but it is easier to read when the
> style is consistent through the library.

It's not a style issue. That template parameter needs to be a non-type one,
otherwise the overloads are ambiguous.

> Introducing
> typename _XXX = _TC<(sizeof...(_Elements) == sizeof...(_UElements)),
> _Elements...>
> and then using _XXX::template thing() might give less clutter when you have
> to repeat it 4 times.

Sounds good, I'll give it a spin.