From 1702853893aa8b699d59e99bd73969c9a8360437 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Fri, 8 Nov 2024 12:58:40 +0100
Subject: [PATCH] refactor: `SymbolicConstant` moved to _expression_template.h_

---
 src/core/include/mp-units/ext/type_traits.h       |  7 -------
 .../mp-units/framework/expression_template.h      | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/core/include/mp-units/ext/type_traits.h b/src/core/include/mp-units/ext/type_traits.h
index 70b9523c..119a27c5 100644
--- a/src/core/include/mp-units/ext/type_traits.h
+++ b/src/core/include/mp-units/ext/type_traits.h
@@ -193,11 +193,4 @@ template<template<auto...> typename T, typename T1, typename T2, typename... Ts>
     return get<T, T2, Ts...>();
 }
 
-namespace detail {
-
-template<typename T>
-concept SymbolicConstant = std::is_empty_v<T> && std::is_final_v<T>;
-
-}
-
 }  // namespace mp_units
diff --git a/src/core/include/mp-units/framework/expression_template.h b/src/core/include/mp-units/framework/expression_template.h
index 17e40512..4514edd9 100644
--- a/src/core/include/mp-units/framework/expression_template.h
+++ b/src/core/include/mp-units/framework/expression_template.h
@@ -31,13 +31,28 @@
 #ifdef MP_UNITS_IMPORT_STD
 import std;
 #else
+#include <concepts>
 #include <cstdint>
 #include <functional>
+#include <type_traits>
 #endif
 #endif
 
 namespace mp_units {
 
+namespace detail {
+
+// `SymbolicArg` is provided because `SymbolicConstant` requires a complete type which is not the case
+// for `OneType` below.
+template<typename T>
+concept SymbolicArg = (!std::is_const_v<T>) && (!std::is_reference_v<T>);
+
+template<typename T>
+concept SymbolicConstant =
+  SymbolicArg<T> && std::is_empty_v<T> && std::is_trivial_v<T> && std::semiregular<T> && std::is_final_v<T>;
+
+}  // namespace detail
+
 /**
  * @brief Type list type used by the expression template framework
  *