From b12b9f87ae275a51876bb14702a22cb2e573e24d Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Sat, 30 Sep 2023 22:14:20 -0600
Subject: [PATCH] feat: `quantity` and `quantity_point` conversion operators
 now can also convert to const references

---
 src/core/include/mp-units/quantity.h       | 10 ++++++----
 src/core/include/mp-units/quantity_point.h |  9 ++++++---
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/quantity.h
index f9fae4d7..afc1ad2b 100644
--- a/src/core/include/mp-units/quantity.h
+++ b/src/core/include/mp-units/quantity.h
@@ -143,7 +143,7 @@ public:
   quantity& operator=(const quantity&) = default;
   quantity& operator=(quantity&&) = default;
 
-  // conversions
+  // unit conversions
   template<UnitCompatibleWith<unit, quantity_spec> U>
     requires detail::QuantityConvertibleTo<quantity, quantity<detail::make_reference(quantity_spec, U{}), Rep>>
   [[nodiscard]] constexpr Quantity auto in(U) const
@@ -192,7 +192,8 @@ public:
   }
 
   // conversion operators
-  template<QuantityLike Q>
+  template<typename Q>
+    requires QuantityLike<std::remove_cvref_t<Q>>
   [[nodiscard]] explicit(is_specialization_of<decltype(quantity_like_traits<Q>::from_numerical_value(numerical_value_)),
                                               convert_explicitly>) constexpr
   operator Q() const& noexcept(noexcept(quantity_like_traits<Q>::from_numerical_value(numerical_value_)) &&
@@ -201,11 +202,12 @@ public:
     return quantity_like_traits<Q>::from_numerical_value(numerical_value_).value;
   }
 
-  template<QuantityLike Q>
+  template<typename Q>
+    requires QuantityLike<std::remove_cvref_t<Q>>
   [[nodiscard]] explicit(is_specialization_of<decltype(quantity_like_traits<Q>::from_numerical_value(numerical_value_)),
                                               convert_explicitly>) constexpr
   operator Q() && noexcept(noexcept(quantity_like_traits<Q>::from_numerical_value(numerical_value_)) &&
-                                std::is_nothrow_move_constructible_v<rep>)
+                           std::is_nothrow_move_constructible_v<rep>)
   {
     return quantity_like_traits<Q>::from_numerical_value(std::move(numerical_value_)).value;
   }
diff --git a/src/core/include/mp-units/quantity_point.h b/src/core/include/mp-units/quantity_point.h
index 068a4a40..3095d0fb 100644
--- a/src/core/include/mp-units/quantity_point.h
+++ b/src/core/include/mp-units/quantity_point.h
@@ -170,6 +170,7 @@ public:
     return *this - PO2{};
   }
 
+  // unit conversions
   template<UnitCompatibleWith<unit, quantity_spec> U>
     requires detail::QuantityConvertibleTo<quantity_type, quantity<detail::make_reference(quantity_spec, U{}), Rep>>
   [[nodiscard]] constexpr QuantityPoint auto in(U) const
@@ -185,7 +186,8 @@ public:
   }
 
   // conversion operators
-  template<QuantityPointLike QP>
+  template<typename QP>
+    requires QuantityPointLike<std::remove_cvref_t<QP>>
   [[nodiscard]] explicit(
     is_specialization_of<decltype(quantity_point_like_traits<QP>::from_quantity(quantity_from_origin_)),
                          convert_explicitly>) constexpr
@@ -195,12 +197,13 @@ public:
     return quantity_point_like_traits<QP>::from_quantity(quantity_from_origin_).value;
   }
 
-  template<QuantityPointLike QP>
+  template<typename QP>
+    requires QuantityPointLike<std::remove_cvref_t<QP>>
   [[nodiscard]] explicit(
     is_specialization_of<decltype(quantity_point_like_traits<QP>::from_quantity(quantity_from_origin_)),
                          convert_explicitly>) constexpr
   operator QP() && noexcept(noexcept(quantity_point_like_traits<QP>::from_quantity(quantity_from_origin_)) &&
-                                 std::is_nothrow_move_constructible_v<rep>)
+                            std::is_nothrow_move_constructible_v<rep>)
   {
     return quantity_point_like_traits<QP>::from_quantity(std::move(quantity_from_origin_)).value;
   }