From a3e5c84a4750dc265c886af19d98dccb2d6d530a Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Wed, 24 May 2023 22:39:42 +0200
Subject: [PATCH] feat: support for convertibility of point origins added

---
 example/include/geographic.h                             | 6 +++---
 example/unmanned_aerial_vehicle.cpp                      | 1 +
 src/core/include/mp_units/bits/quantity_point_concepts.h | 2 +-
 src/core/include/mp_units/quantity_point.h               | 7 ++++++-
 4 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/example/include/geographic.h b/example/include/geographic.h
index b3268393..1c514cde 100644
--- a/example/include/geographic.h
+++ b/example/include/geographic.h
@@ -37,9 +37,9 @@
 
 namespace geographic {
 
-// clang-format off
-inline constexpr struct mean_sea_level : mp_units::absolute_point_origin<mp_units::isq::altitude> {} mean_sea_level;
-// clang-format on
+inline constexpr struct mean_sea_level : mp_units::absolute_point_origin<mp_units::isq::altitude> {
+  using mp_units::absolute_point_origin<mp_units::isq::altitude>::absolute_point_origin;
+} mean_sea_level;
 
 using msl_altitude = mp_units::quantity_point<mp_units::isq::altitude[mp_units::si::metre], mean_sea_level>;
 
diff --git a/example/unmanned_aerial_vehicle.cpp b/example/unmanned_aerial_vehicle.cpp
index 31f41e84..f8dee6d6 100644
--- a/example/unmanned_aerial_vehicle.cpp
+++ b/example/unmanned_aerial_vehicle.cpp
@@ -38,6 +38,7 @@ enum class earth_gravity_model { egm84_15, egm95_5, egm2008_1 };
 template<earth_gravity_model M>
 struct height_above_ellipsoid_t : absolute_point_origin<isq::altitude> {
   static constexpr earth_gravity_model egm = M;
+  using absolute_point_origin<isq::altitude>::absolute_point_origin;
 };
 template<earth_gravity_model M>
 inline constexpr height_above_ellipsoid_t<M> height_above_ellipsoid;
diff --git a/src/core/include/mp_units/bits/quantity_point_concepts.h b/src/core/include/mp_units/bits/quantity_point_concepts.h
index 3f20b08f..197a9da8 100644
--- a/src/core/include/mp_units/bits/quantity_point_concepts.h
+++ b/src/core/include/mp_units/bits/quantity_point_concepts.h
@@ -98,7 +98,7 @@ concept QuantityPointOf =
   QuantityPoint<QP> &&
   (ReferenceOf<std::remove_const_t<decltype(QP::reference)>, V> ||
    (PointOrigin<std::remove_const_t<decltype(V)>> &&
-    std::same_as<std::remove_const_t<decltype(QP::absolute_point_origin)>, std::remove_const_t<decltype(V)>>));
+    std::convertible_to<std::remove_const_t<decltype(QP::absolute_point_origin)>, std::remove_const_t<decltype(V)>>));
 
 /**
  * @brief A concept matching all external quantity point like types
diff --git a/src/core/include/mp_units/quantity_point.h b/src/core/include/mp_units/quantity_point.h
index 59c574c6..d9077e04 100644
--- a/src/core/include/mp_units/quantity_point.h
+++ b/src/core/include/mp_units/quantity_point.h
@@ -1,4 +1,3 @@
-
 // The MIT License (MIT)
 //
 // Copyright (c) 2018 Mateusz Pusz
@@ -33,6 +32,12 @@ namespace mp_units {
 template<QuantitySpec auto Q>
 struct absolute_point_origin {
   static constexpr QuantitySpec auto quantity_spec = Q;
+  absolute_point_origin() = default;
+  template<QuantitySpec auto Q2>
+    requires(implicitly_convertible(Q2, Q))
+  consteval absolute_point_origin(absolute_point_origin<Q2>)
+  {
+  }
 };
 
 namespace detail {