From b96be72457118863cc41c82b941cdec6fb0e5ea4 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Sun, 15 Oct 2023 09:39:18 +0200
Subject: [PATCH] feat: :boom: `quantity_point` does not provide `zero()`
 anymore

---
 example/include/geographic.h                  | 28 +++++++++----------
 src/core/include/mp-units/quantity_point.h    |  6 ----
 test/unit_test/static/quantity_point_test.cpp |  4 ---
 3 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/example/include/geographic.h b/example/include/geographic.h
index b704dd245..d68308963 100644
--- a/example/include/geographic.h
+++ b/example/include/geographic.h
@@ -79,19 +79,21 @@ using longitude = mp_units::quantity_point<mp_units::si::degree, prime_meridian,
 template<class CharT, class Traits, typename T>
 std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const latitude<T>& lat)
 {
-  if (is_gteq_zero(lat))
-    return os << lat.quantity_from_origin() << " N";
+  const auto& q = lat.quantity_ref_from(geographic::equator);
+  if (is_gteq_zero(q))
+    return os << q << " N";
   else
-    return os << -lat.quantity_from_origin() << " S";
+    return os << -q << " S";
 }
 
 template<class CharT, class Traits, typename T>
 std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const longitude<T>& lon)
 {
-  if (is_gteq_zero(lon))
-    return os << lon.quantity_from_origin() << " E";
+  const auto& q = lon.quantity_ref_from(geographic::prime_meridian);
+  if (is_gteq_zero(q))
+    return os << q << " E";
   else
-    return os << -lon.quantity_from_origin() << " W";
+    return os << -q << " W";
 }
 
 inline namespace literals {
@@ -137,9 +139,9 @@ struct MP_UNITS_STD_FMT::formatter<geographic::latitude<T>> :
   template<typename FormatContext>
   auto format(geographic::latitude<T> lat, FormatContext& ctx)
   {
-    formatter<typename geographic::latitude<T>::quantity_type>::format(
-      is_gteq_zero(lat) ? lat.quantity_from(geographic::equator) : -lat.quantity_from(geographic::equator), ctx);
-    MP_UNITS_STD_FMT::format_to(ctx.out(), "{}", is_gteq_zero(lat) ? " N" : "S");
+    const auto& q = lat.quantity_ref_from(geographic::equator);
+    formatter<typename geographic::latitude<T>::quantity_type>::format(is_gteq_zero(q) ? q : -q, ctx);
+    MP_UNITS_STD_FMT::format_to(ctx.out(), "{}", is_gteq_zero(q) ? " N" : "S");
     return ctx.out();
   }
 };
@@ -150,11 +152,9 @@ struct MP_UNITS_STD_FMT::formatter<geographic::longitude<T>> :
   template<typename FormatContext>
   auto format(geographic::longitude<T> lon, FormatContext& ctx)
   {
-    formatter<typename geographic::longitude<T>::quantity_type>::format(
-      is_gteq_zero(lon) ? lon.quantity_from(geographic::prime_meridian)
-                        : -lon.quantity_from(geographic::prime_meridian),
-      ctx);
-    MP_UNITS_STD_FMT::format_to(ctx.out(), "{}", is_gteq_zero(lon) ? " E" : " W");
+    const auto& q = lon.quantity_ref_from(geographic::prime_meridian);
+    formatter<typename geographic::longitude<T>::quantity_type>::format(is_gteq_zero(q) ? q : -q, ctx);
+    MP_UNITS_STD_FMT::format_to(ctx.out(), "{}", is_gteq_zero(q) ? " E" : " W");
     return ctx.out();
   }
 };
diff --git a/src/core/include/mp-units/quantity_point.h b/src/core/include/mp-units/quantity_point.h
index 6cf8308bd..9d71c3c54 100644
--- a/src/core/include/mp-units/quantity_point.h
+++ b/src/core/include/mp-units/quantity_point.h
@@ -85,12 +85,6 @@ class quantity_point {
   quantity_type quantity_from_origin_;  // needs to be public for a structural type
 
   // static member functions
-  [[nodiscard]] static constexpr quantity_point zero() noexcept
-    requires requires { quantity_type::zero(); }
-  {
-    return quantity_point(quantity_type::zero());
-  }
-
   [[nodiscard]] static constexpr quantity_point min() noexcept
     requires requires { quantity_type::min(); }
   {
diff --git a/test/unit_test/static/quantity_point_test.cpp b/test/unit_test/static/quantity_point_test.cpp
index 46e0b6d11..0368f30ba 100644
--- a/test/unit_test/static/quantity_point_test.cpp
+++ b/test/unit_test/static/quantity_point_test.cpp
@@ -240,15 +240,11 @@ static_assert(
 // static member functions
 ////////////////////////////
 
-static_assert(quantity_point<isq::height[m], mean_sea_level>::zero().quantity_from_origin_.numerical_value_ == 0);
 static_assert(quantity_point<isq::height[m], mean_sea_level>::min().quantity_from_origin_.numerical_value_ ==
               std::numeric_limits<double>::lowest());
 static_assert(quantity_point<isq::height[m], mean_sea_level>::max().quantity_from_origin_.numerical_value_ ==
               std::numeric_limits<double>::max());
 
-static_assert(
-
-  quantity_point<isq::height[m], ground_level, int>::zero().quantity_from_origin_.numerical_value_ == 0);
 static_assert(quantity_point<isq::height[m], ground_level, int>::min().quantity_from_origin_.numerical_value_ ==
               std::numeric_limits<int>::lowest());
 static_assert(quantity_point<isq::height[m], ground_level, int>::max().quantity_from_origin_.numerical_value_ ==