From 6f0f6b2213d32c48eb1a4285cffde00907b477e9 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Thu, 8 Jun 2023 17:41:48 +0200
Subject: [PATCH] feat: `make_quantity()` and `op*(Representation, Unit` are
 now correctly using quantity constructor constraints

---
 src/core/include/mp-units/quantity.h      | 7 +++++--
 src/core/include/mp-units/quantity_spec.h | 2 +-
 src/core/include/mp-units/reference.h     | 4 ++--
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/quantity.h
index 748d9efc..6579a5c0 100644
--- a/src/core/include/mp-units/quantity.h
+++ b/src/core/include/mp-units/quantity.h
@@ -99,6 +99,9 @@ public:
   static constexpr Unit auto unit = get_unit(reference);
   using rep = Rep;
 
+  // helper used to constrain `make_quantity()` and `operator*(Representation, Unit)`
+  static constexpr bool _rep_safe_constructible_ = detail::RepSafeConstructibleFrom<Rep, Rep&&, unit>;
+
   // static member functions
   [[nodiscard]] static constexpr quantity zero() noexcept
     requires requires { quantity_values<rep>::zero(); }
@@ -319,7 +322,7 @@ public:
 
 private:
   template<Reference auto R2, typename Rep2>
-    requires RepresentationOf<std::remove_cvref_t<Rep2>, get_quantity_spec(R2).character>
+    requires quantity<R2, std::remove_cvref_t<Rep2>>::_rep_safe_constructible_
   friend constexpr quantity<R2, std::remove_cvref_t<Rep2>> make_quantity(Rep2&& v);
 
   template<typename Value>
@@ -488,7 +491,7 @@ template<auto R, typename Rep, typename Value>
 
 // make_quantity
 template<Reference auto R, typename Rep>
-  requires RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R).character>
+  requires quantity<R, std::remove_cvref_t<Rep>>::_rep_safe_constructible_
 [[nodiscard]] constexpr quantity<R, std::remove_cvref_t<Rep>> make_quantity(Rep&& v)
 {
   return quantity<R, std::remove_cvref_t<Rep>>(std::forward<Rep>(v));
diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index 89e27c7b..e6e3013e 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -37,7 +37,7 @@
 namespace mp_units {
 
 template<Reference auto R, typename Rep>
-  requires RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R).character>
+  requires quantity<R, std::remove_cvref_t<Rep>>::_rep_safe_constructible_
 [[nodiscard]] constexpr quantity<R, std::remove_cvref_t<Rep>> make_quantity(Rep&& v);
 
 namespace detail {
diff --git a/src/core/include/mp-units/reference.h b/src/core/include/mp-units/reference.h
index c120bb75..120d27be 100644
--- a/src/core/include/mp-units/reference.h
+++ b/src/core/include/mp-units/reference.h
@@ -30,7 +30,7 @@
 namespace mp_units {
 
 template<Reference auto R, typename Rep>
-  requires RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R).character>
+  requires quantity<R, std::remove_cvref_t<Rep>>::_rep_safe_constructible_
 [[nodiscard]] constexpr quantity<R, std::remove_cvref_t<Rep>> make_quantity(Rep&& v);
 
 [[nodiscard]] consteval QuantitySpec auto get_quantity_spec(AssociatedUnit auto u)
@@ -129,7 +129,7 @@ template<Reference auto R, RepresentationOf<get_quantity_spec(R).character> Rep>
 class quantity;
 
 template<typename Rep, Reference R>
-  requires RepresentationOf<std::remove_cvref_t<Rep>, get_quantity_spec(R{}).character>
+  requires quantity<R{}, std::remove_cvref_t<Rep>>::_rep_safe_constructible_
 [[nodiscard]] constexpr quantity<R{}, std::remove_cvref_t<Rep>> operator*(Rep&& lhs, R)
 {
   return make_quantity<R{}>(std::forward<Rep>(lhs));