[libcxx-commits] [PATCH] D112631: [libc++][test] Fix invalid test for views::view_interface

[Mark de Wever via Phabricator via libcxx-commits]

Mordante added a comment.

In D112631#3091418 <https://reviews.llvm.org/D112631#3091418>, @cjdb wrote:

> There seems to be some confusion about whether or not this deviates from standard wording. It doesn't. I would very much prefer that our implementation catch user errors whenever we're in a position to do so, rather than let our users get false positives for a valid C++ program.

I agree we should catch it, but I dislike to change the public interface from the wording in the Standard. Hence my suggestion to add these additional constraints to the exposition only functions. IMO that's the better solution:

- The public interface follows the wording of the Standard.
- The additional constrains only need to be applied to two functions instead of all public functions.

So I prefer

  _LIBCPP_HIDE_FROM_ABI
  constexpr _Derived& __derived() noexcept requires view<D> && derived_from<D, view_interface<D>>
  {
    return static_cast<_Derived&>(*this);
  }

over

  template<class _D2 = _Derived>
  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty()
    noexcept(noexcept(__implicitly_convert_to<bool>(ranges::begin(__derived()) == ranges::end(__derived()))))
    requires forward_range<_D2> && requires view<D> && derived_from<D, view_interface<D>>
  {
    return ranges::begin(__derived()) == ranges::end(__derived());
  }




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https://reviews.llvm.org/D112631