From b32363b848d47872732fcfc3a5ecd52e6f476c0e Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Wed, 24 Apr 2024 11:32:37 -0400
Subject: [PATCH] xo-unit: + (Quantity * Dimensionless) and vice versa

---
 include/xo/unit/Quantity.hpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/xo/unit/Quantity.hpp b/include/xo/unit/Quantity.hpp
index aaf29d73..d24f2589 100644
--- a/include/xo/unit/Quantity.hpp
+++ b/include/xo/unit/Quantity.hpp
@@ -214,6 +214,24 @@ namespace xo {
             return Quantity::multiply(x, y);
         }
 
+        /** note: does not require unit scaling,  so constexpr with c++23 **/
+        template <typename Dimensionless, typename Quantity>
+        requires std::is_arithmetic_v<Dimensionless> && quantity2_concept<Quantity>
+        constexpr auto
+        operator* (Dimensionless x, const Quantity & y)
+        {
+            return y.scale_by(x);
+        }
+
+        /** note: does not require unit scaling,  so constexpr with c++23 **/
+        template <typename Dimensionless, typename Quantity>
+        requires std::is_arithmetic_v<Dimensionless> && quantity2_concept<Quantity>
+        constexpr auto
+        operator* (const Quantity & x, Dimensionless y)
+        {
+            return x.scale_by(y);
+        }
+
         /** note: won't have constexpr result until c++26 (when ::sqrt(), ::pow() are constexpr)
          **/
         template <typename Quantity, typename Quantity2>