[libcxx-commits] [libcxx] [libc++] Refactor __tuple_like and __pair_like (PR #85206)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___TUPLE_TUPLE_LIKE_NO_SUBRANGE_H
+#define _LIBCPP___TUPLE_TUPLE_LIKE_NO_SUBRANGE_H
+
+#include <__config>
+#include <__fwd/array.h>
+#include <__fwd/complex.h>
+#include <__fwd/pair.h>
+#include <__fwd/tuple.h>
+#include <__tuple/tuple_size.h>
+#include <__type_traits/remove_cvref.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _Tp>
+inline constexpr bool __tuple_like_no_subrange_impl = false;
+
+template <class... _Tp>
+inline constexpr bool __tuple_like_no_subrange_impl<tuple<_Tp...>> = true;
+
+template <class _T1, class _T2>
+inline constexpr bool __tuple_like_no_subrange_impl<pair<_T1, _T2>> = true;
+
+template <class _Tp, size_t _Size>
+inline constexpr bool __tuple_like_no_subrange_impl<array<_Tp, _Size>> = true;
+
+#  if _LIBCPP_STD_VER >= 26
+
+template <class _Tp>
+inline constexpr bool __tuple_like_no_subrange_impl<complex<_Tp>> = true;
+
+#  endif
+
+template <class _Tp>
+concept __tuple_like_no_subrange = __tuple_like_no_subrange_impl<remove_cvref_t<_Tp>>;
+
+// This is equivalent to the exposition-only type trait `pair-like`, except that it is false for specializations of
+// `ranges::subrange`. This is removed, because every use of `pair-like` excludes `ranges::subrange`.
----------------
ldionne wrote:

```suggestion
// `ranges::subrange`. This is more useful than the pair-like concept in the Standard because every use of pair-like also excludes ranges::subrange.
```

https://github.com/llvm/llvm-project/pull/85206