refactor: conversion from quantity to quantity_point is now explicit

example/currency.cpp

@@ -78,7 +78,7 @@ quantity<To, Rep> exchange_to(quantity<From, Rep> q)
 template<ReferenceOf<currency> auto To, ReferenceOf<currency> auto From, auto PO, typename Rep>
 quantity_point<To, PO, Rep> exchange_to(quantity_point<From, PO, Rep> q)
 {
-  return static_cast<Rep>(exchange_rate<q.unit, get_unit(To)>() * q.absolute().number()) * To;
+  return quantity_point{static_cast<Rep>(exchange_rate<q.unit, get_unit(To)>() * q.absolute().number()) * To};
 }
 
 int main()

example/unmanned_aerial_vehicle.cpp

@@ -97,7 +97,7 @@ hae_altitude<M> to_hae(msl_altitude msl, position<long double> pos)
 {
   const auto geoid_undulation =
     isq::height(GeographicLibWhatsMyOffset(pos.lat.number_in(si::degree), pos.lon.number_in(si::degree)) * si::metre);
-  return msl.absolute() - geoid_undulation;
+  return hae_altitude<M>{msl.absolute() - geoid_undulation};
 }
 
 
@@ -129,7 +129,7 @@ struct STD_FMT::formatter<hal_altitude> : formatter<hal_altitude::quantity_type>
 // **** UAV ****
 
 class unmanned_aerial_vehicle {
-  msl_altitude current_ = 0 * si::metre;
+  msl_altitude current_{0 * si::metre};
   msl_altitude launch_ = current_;
 public:
   void take_off(msl_altitude alt) { launch_ = alt; }
@@ -138,7 +138,7 @@ public:
   void current(msl_altitude alt) { current_ = alt; }
   msl_altitude current() const { return current_; }
 
-  hal_altitude hal() const { return current_ - launch_; }
+  hal_altitude hal() const { return hal_altitude{current_ - launch_}; }
 };
 
 
@@ -148,11 +148,11 @@ int main()
   using namespace mp_units::international::unit_symbols;
 
   unmanned_aerial_vehicle uav;
-  uav.take_off(6'000 * ft);
-  uav.current(10'000 * ft);
+  uav.take_off(msl_altitude{6'000 * ft});
+  uav.current(msl_altitude{10'000 * ft});
   std::cout << STD_FMT::format("hal = {}\n", uav.hal());
 
-  msl_altitude ground_level = 123 * m;
+  msl_altitude ground_level{123 * m};
   std::cout << STD_FMT::format("agl = {}\n", uav.current() - ground_level);
 
   struct waypoint {

src/core/include/mp_units/quantity_point.h

@@ -102,7 +102,7 @@ public:
 
   template<typename T>
     requires std::constructible_from<quantity_type, T>
-  constexpr explicit(!std::convertible_to<T, quantity_type>) quantity_point(T&& v) : q_(std::forward<T>(v))
+  constexpr explicit quantity_point(T&& v) : q_(std::forward<T>(v))
   {
   }