[libc++/clang] std::ranges::views::take does not work with | operator

[mattreecebentley]

The following code in C++20:

#include <vector>
#include <ranges>


int main()
{
	std::vector<int> i_vec({1, 2, 3});
	auto rng = i_vec | std::ranges::views::take(2);
	return 0;
}

Produces the following error in Clang 14.00:

<source>:8:19: error: invalid operands to binary expression ('std::vector<int>' and '_Partial<std::ranges::views::_Take, decay_t<int>>' (aka '_Partial<std::ranges::views::_Take, int>'))
        auto rng = i_vec | std::ranges::views::take(2);

Godbolt: https://godbolt.org/z/c35r4Pa1h

The code as far as I can tell, is valid and works in GCC11 and MSVC 2022.
Unsure whether this is a libc++ or clang bug.

[llvmbot]

@llvm/issue-subscribers-c-20

[cpplearner]

Well, the godbolt link uses libstdc++, so it's certainly not a libc++ bug.

I believe that libstdc++'s <ranges> does not work with clang at all, because clang's support for concepts is incomplete.

[mattreecebentley]

That would make sense.

…

On 25/05/2022 2:04 am, S. B. Tam wrote: Well, the godbolt link uses libstdc++, so it's certainly not a libc++ bug. I believe that libstdc++'s |<range>| does not work with clang at all, because clang's support for concepts is incomplete. — Reply to this email directly, view it on GitHub <#55673 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABE4FIXH5TUY7HWJT54W5QDVLTOXHANCNFSM5WZAWGKQ>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[erichkeane]

Is this a duplicate of the 'deferred concepts' feature? A lot of the ranges::views stuff ends up having that problem. Patch is in progress/1 bug left (AFAIK) here: https://reviews.llvm.org/D126907#3574083

I note that the preprocessed version of this ends up crashing in my patch in std::vector, but it is hopefully the same issue that I'm already looking into.

[royjacobson]

Works after https://reviews.llvm.org/D126907, so this was a duplicate of #44178 indeed.