[libcxx-commits] [libcxx] [libc++][format][NFC] Granularize `__fmt_pair_like` (PR #150583)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,47 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___FORMAT_FMT_PAIR_LIKE_H
+#define _LIBCPP___FORMAT_FMT_PAIR_LIKE_H
+
+#include <__config>
+#include <__fwd/pair.h>
+#include <__fwd/tuple.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+// [tuple.like] defines a tuple-like exposition only concept. This concept is not related to that. Therefore it uses a
+// different name for the concept.
+//
+// TODO FMT Add a test to validate we fail when using that concept after P2165 has been implemented.
+
+// [format.range.fmtkind]/2.2.1 and [tab:formatter.range.type]:
+// "U is either a specialization of pair or a specialization of tuple such that tuple_size_v<U> is 2."
+// We use an alternative approach to avoid dragging in many templates.
+template <class>
+inline constexpr bool __is_fmt_pair_like_v = false;
+template <class _Tp, class _Up>
+inline constexpr bool __is_fmt_pair_like_v<pair<_Tp, _Up>> = true;
+template <class _Tp, class _Up>
+inline constexpr bool __is_fmt_pair_like_v<tuple<_Tp, _Up>> = true;
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frederick-vs-ja wrote:

OK. I'm switching back to the original implementation.

https://github.com/llvm/llvm-project/pull/150583