From 86743d6d247127c04279c2038f4ad8f5595759a3 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Thu, 18 Apr 2024 22:41:13 +0100
Subject: [PATCH] fix: `std::formattable` usage is now conditional

---
 src/core/include/mp-units/format.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/core/include/mp-units/format.h b/src/core/include/mp-units/format.h
index 74f57580..18b1e5c8 100644
--- a/src/core/include/mp-units/format.h
+++ b/src/core/include/mp-units/format.h
@@ -265,7 +265,11 @@ public:
 // subentity-id                ::= 'N' | 'U' | 'D'
 // format-spec                 ::= <as specified by the formatter for the argument type>
 //
+#if __cpp_lib_format_ranges
 template<auto Reference, typename Char, std::formattable<Char> Rep>
+#else
+template<auto Reference, typename Rep, typename Char>
+#endif
 class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
   static constexpr auto unit = get_unit(Reference);
   static constexpr auto dimension = get_quantity_spec(Reference).dimension;