There has been work towards universal template parameters (<
https://wg21.link/P1985R3>), and probably the most generic thing that could
be added is something like
`std::apply(std::constructor_for<std::ranges::subrange>, pair)`. This would
also allow `std::ranges::to` for templates with {constant,template}
template parameters

On Sat, 6 Jun 2026, 01:46 Keenan Horrigan via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> For what it's worth, this could be done in C++26 if you would find it
> acceptable to spell it instead as
>
> auto subrange = make_from_tuple<^^ranges::subrange>(m.equal_range(1));
>
> If you accept a std::meta::info in the template parameter for
> make_from_tuple.
>
> It's likely still beneficial to pursue universal templates as a language
> feature, but if you just wanted to write your own version of this function
> then you can in C++26.
>
> On Friday, June 5th, 2026 at 10:39 AM, Hewill Kang via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>
>
> Rainer Deyke via Std-Proposals <std-proposals_at_[hidden]> 於
> 2026年6月5日週五 下午11:23寫道：
>
>>
>>
>> On 6/5/26 14:40, Hewill Kang wrote:
>> > Rainer Deyke via Std-Proposals <std-proposals_at_[hidden]> 於
>> > 2026年6月5日週五 下午6:09寫道：
>> >> Add a free function to convert a std::pair of iterators into a
>> >> std::ranges::subrange. This is the safest solution; highly unlikely to
>> >> break user code and any user code it does breaks is the fault of the
>> user.
>> >>
>> >>
>> > Yep, but it can be done very easily with:
>> >
>> > auto to_subrange = [](auto&&... iters) { return
>> > std::ranges::subrange(iters...); };
>> > auto subrange = std::apply(to_subrange, m.equal_range(1));
>>
>> Yes, it's a fairly simple function to write. The same can be said for
>> much of the standard library.
>>
>> Once I have a named function, I need to worry about what to name it,
>> where to put it, and how to package it and distribute to where it needs
>> to go. I either need to put this function in an existing library,
>> create a new library just for the function, or write the function over
>> and over again for every project that needs it. Possible, but annoying.
>>
>> Or I could just not name the function.
>>
>> auto subrange = [](auto &&p){ return std::ranges::subrange(p.first,
>> p.second); }(m.equal_range(1));
>>
>> Not quite as idiomatic as I would like, but it works.
>>
>>
>>
> This is why I would be happy to see the standard introduce a universe
> template version of `make_from_tuple` if we once have a universe template,
> for example:
>
> template<template<universal template...> typename Templ, *tuple-like*
> Tuple>
> constexpr auto make_from_tuple(Tuple&& t);
>
> This allows us to spell things like the following:
>
> auto subrange = make_from_tuple<ranges::subrange>(m.equal_range(1));
>
> Using `template<template<typename...> typename Templ, tuple-like Tuple>`
> will not work because the template parameter of `subrange` is
> `template<class, class, subrange_kind>`, the last one is NTTP.
>
> --
>> Rainer Deyke - rainerd_at_[hidden]
>>
>> --
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