From 0dfd323c4b3346009a3ab72685fccd322815d1fe Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Sun, 14 Jul 2024 18:06:02 +0200
Subject: [PATCH] feat: `ValuePreservingTo` extended with the explicit
 convertibility requirement

---
 src/core/include/mp-units/framework/quantity.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/core/include/mp-units/framework/quantity.h b/src/core/include/mp-units/framework/quantity.h
index 936c227e..279e81a7 100644
--- a/src/core/include/mp-units/framework/quantity.h
+++ b/src/core/include/mp-units/framework/quantity.h
@@ -60,8 +60,11 @@ template<typename T>
 concept IsFloatingPoint = treat_as_floating_point<T>;
 
 template<typename FromRep, typename ToRep, auto FromUnit = one, auto ToUnit = one>
-concept ValuePreservingTo =
-  IsFloatingPoint<ToRep> || (!IsFloatingPoint<FromRep> && (integral_conversion_factor(FromUnit, ToUnit)));
+concept ValuePreservingTo = requires(FromRep&& from, ToRep to) {
+  {
+    to = std::forward<FromRep>(from)
+  } -> std::same_as<ToRep&>;
+} && (IsFloatingPoint<ToRep> || (!IsFloatingPoint<FromRep> && (integral_conversion_factor(FromUnit, ToUnit))));
 
 template<typename QFrom, typename QTo>
 concept QuantityConvertibleTo =