Re: [boost] Proposal: boost::make_array()

Subject: Re: [boost] Proposal: boost::make_array()
From: Kyle Lutz (kyle.r.lutz_at_[hidden])
Date: 2013-01-16 00:40:07

On Sun, Jan 13, 2013 at 2:39 PM, Kyle Lutz <kyle.r.lutz_at_[hidden]> wrote:
>
> On Sun, Jan 13, 2013 at 11:23 AM, Thomas Heller <thom.heller_at_[hidden]>
wrote:
> >
> > On Sunday, January 13, 2013 14:36:50 Mathias Gaunard wrote:
> > > On 13/01/2013 10:38, Thomas Heller wrote:
> > > > The C++11 code looks too complicated. Wouldn't
> > > > https://gist.github.com/4522812 be enough?
>
> Indeed it is! I've updated the C++11 code to use the simpler
initialization method. Thanks!
>
> > >
> > > I don't think it is a good idea that make_array(1, 1., 1.f) makes an
> > > array of int.
> > > It seems quite arbitrary that the first argument would decide the
type.
> >
> > Right. That is another problem. I just tried to simplify the
implementation of
> > the original proposal.
>
> As far as type-deduction, how would you guys feel about an implementation
using boost::common_type? Something along the lines of:
>
> // make_array with deduced type
> template<class... Args>
> inline array<typename common_type<Args...>::type, sizeof...(Args)>
> make_array(Args&&... args)
> {
>     typedef typename common_type<Args...>::type T;
>
>     return
>         array<T, sizeof...(Args)> {{
>             static_cast<T>(std::forward<Args>(args))...
>         }};
> }
>
> So that make_array(1, 2.1f) would return array<float, 2> and
make_array(1, 2.1f, 3.2) would return array<double, 3>.
>
> Thoughts?
>
> Thanks,
> Kyle
>

Thanks for the feedback everyone!

I've updated the make_array() function to use boost::common_type<> to do
the type-deduction instead of always using the type of the first argument.
Furthermore, explicitly specifying the array's value type is still
supported.

To better illustrate, here's a set of make_array() invocations along with
the return type:

make_array(1) => array<int, 1>
make_array<float>(1) => array<float, 1>
make_array(1, 1.2f) => array<float, 2>
make_array<int>(1, 1.2f) => array<int, 2>
make_array(1, 1.2f, 3.2) => array<double, 3>

Thoughts/comments?

Cheers,
Kyle