From ccdf5d319a001245672042c0f32dd2b0073f91b6 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Wed, 2 Aug 2023 11:20:32 +0200
Subject: [PATCH] feat: `point_from` extended with the case of the same origin

---
 src/core/include/mp-units/quantity_point.h    | 4 +++-
 test/unit_test/static/quantity_point_test.cpp | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/core/include/mp-units/quantity_point.h b/src/core/include/mp-units/quantity_point.h
index ced82c60..535a16e0 100644
--- a/src/core/include/mp-units/quantity_point.h
+++ b/src/core/include/mp-units/quantity_point.h
@@ -142,7 +142,9 @@ public:
   template<PointOriginFor<quantity_spec> NewPO>
   [[nodiscard]] constexpr QuantityPointOf<NewPO{}> auto point_from(NewPO origin) const
   {
-    if constexpr (detail::is_derived_from_specialization_of_relative_point_origin<NewPO>) {
+    if constexpr (std::is_same_v<NewPO, std::remove_const_t<decltype(point_origin)>>) {
+      return *this;
+    } else if constexpr (detail::is_derived_from_specialization_of_relative_point_origin<NewPO>) {
       auto q = absolute() - origin.quantity_point.absolute();
       return quantity_point<reference, NewPO{}, typename decltype(q)::rep>(std::move(q));
     } else {
diff --git a/test/unit_test/static/quantity_point_test.cpp b/test/unit_test/static/quantity_point_test.cpp
index c6a0d35a..becf1062 100644
--- a/test/unit_test/static/quantity_point_test.cpp
+++ b/test/unit_test/static/quantity_point_test.cpp
@@ -410,12 +410,15 @@ static_assert(quantity_point<isq::height[m], tower_peak>(quantity_point<isq::hei
 static_assert(quantity_point<isq::height[m], tower_peak>(quantity_point<isq::height[m], ground_level>(84 * m))
                 .relative() == 42 * m);
 
+static_assert(quantity_point<isq::height[m], mean_sea_level>(42 * m).point_from(mean_sea_level).relative() == 42 * m);
 static_assert(quantity_point<isq::height[m], ground_level>(42 * m).point_from(mean_sea_level).relative() == 84 * m);
 static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(mean_sea_level).relative() == 126 * m);
 
+static_assert(quantity_point<isq::height[m], ground_level>(84 * m).point_from(ground_level).relative() == 84 * m);
 static_assert(quantity_point<isq::height[m], mean_sea_level>(84 * m).point_from(ground_level).relative() == 42 * m);
 static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(ground_level).relative() == 84 * m);
 
+static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(tower_peak).relative() == 42 * m);
 static_assert(quantity_point<isq::height[m], mean_sea_level>(42 * m).point_from(tower_peak).relative() == -42 * m);
 static_assert(quantity_point<isq::height[m], ground_level>(84 * m).point_from(tower_peak).relative() == 42 * m);
 
@@ -448,12 +451,15 @@ static_assert(quantity_point<isq::height[m], tower_peak>(quantity_point<isq::hei
 static_assert(quantity_point<isq::height[m], tower_peak>(quantity_point<isq::height[m], ground_level>(84 * m))
                 .absolute() == 126 * m);
 
+static_assert(quantity_point<isq::height[m], mean_sea_level>(42 * m).point_from(mean_sea_level).absolute() == 42 * m);
 static_assert(quantity_point<isq::height[m], ground_level>(42 * m).point_from(mean_sea_level).absolute() == 84 * m);
 static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(mean_sea_level).absolute() == 126 * m);
 
+static_assert(quantity_point<isq::height[m], ground_level>(42 * m).point_from(ground_level).absolute() == 84 * m);
 static_assert(quantity_point<isq::height[m], mean_sea_level>(84 * m).point_from(ground_level).absolute() == 84 * m);
 static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(ground_level).absolute() == 126 * m);
 
+static_assert(quantity_point<isq::height[m], tower_peak>(42 * m).point_from(tower_peak).absolute() == 126 * m);
 static_assert(quantity_point<isq::height[m], mean_sea_level>(42 * m).point_from(tower_peak).absolute() == 42 * m);
 static_assert(quantity_point<isq::height[m], ground_level>(84 * m).point_from(tower_peak).absolute() == 126 * m);