From 5cbe322c82e4985f792be89a4ad8569f03f43511 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Wed, 30 Nov 2022 10:11:52 +0100
Subject: [PATCH] feat: `common_reference`, `common_dimension`, and
 `common_units` now take variadic list of arguments

---
 src/core/include/units/dimension.h | 29 ++++++++-----
 src/core/include/units/quantity.h  | 12 +++---
 src/core/include/units/reference.h | 12 +++---
 src/core/include/units/unit.h      | 69 ++++++++++++++++--------------
 4 files changed, 66 insertions(+), 56 deletions(-)

diff --git a/src/core/include/units/dimension.h b/src/core/include/units/dimension.h
index 9e292a9f..3c1a166b 100644
--- a/src/core/include/units/dimension.h
+++ b/src/core/include/units/dimension.h
@@ -328,6 +328,25 @@ template<Dimension D1, Dimension D2>
   return std::derived_from<D1, D2> || std::derived_from<D2, D1>;
 }
 
+[[nodiscard]] consteval auto common_dimension(Dimension auto d) { return d; }
+
+template<Dimension D1, Dimension D2>
+[[nodiscard]] consteval auto common_dimension(D1 d1, D2 d2)
+  requires(interconvertible(d1, d2))
+{
+  if constexpr (std::derived_from<D1, D2>)
+    return d1;
+  else
+    return d2;
+}
+
+[[nodiscard]] consteval auto common_dimension(Dimension auto d1, Dimension auto d2, Dimension auto d3,
+                                              Dimension auto... rest)
+  requires requires { common_dimension(common_dimension(d1, d2), d3, rest...); }
+{
+  return common_dimension(common_dimension(d1, d2), d3, rest...);
+}
+
 /**
  * @brief Computes the value of a dimension raised to the `Num/Den` power
  *
@@ -384,16 +403,6 @@ template<Unit auto U, Dimension auto Dim>
   requires requires { detail::get_dimension_for(U); } && (interconvertible(Dim, detail::get_dimension_for(U)))
 inline constexpr bool is_valid_unit_for_dimension<U, Dim> = true;
 
-template<Dimension D1, Dimension D2>
-[[nodiscard]] consteval auto common_dimension(D1 d1, D2 d2)
-  requires(interconvertible(d1, d2))
-{
-  if constexpr (std::derived_from<D1, D2>)
-    return d1;
-  else
-    return d2;
-}
-
 }  // namespace detail
 
 // TODO consider adding the support for text output of the dimensional equation
diff --git a/src/core/include/units/quantity.h b/src/core/include/units/quantity.h
index 6ce49556..7ecece09 100644
--- a/src/core/include/units/quantity.h
+++ b/src/core/include/units/quantity.h
@@ -481,7 +481,7 @@ template<Quantity Q1, Quantity Q2>
           quantity_value_for_<std::plus<>, typename Q1::rep, typename Q2::rep>
 [[nodiscard]] constexpr Quantity auto operator+(const Q1& lhs, const Q2& rhs)
 {
-  constexpr auto ref = detail::common_reference(Q1::reference, Q2::reference);
+  constexpr auto ref = common_reference(Q1::reference, Q2::reference);
   using ret = quantity<ref, decltype(lhs.number() + rhs.number())>;
   return ret(ret(lhs).number() + ret(rhs).number());
 }
@@ -491,7 +491,7 @@ template<Quantity Q1, Quantity Q2>
           quantity_value_for_<std::minus<>, typename Q1::rep, typename Q2::rep>
 [[nodiscard]] constexpr Quantity auto operator-(const Q1& lhs, const Q2& rhs)
 {
-  constexpr auto ref = detail::common_reference(Q1::reference, Q2::reference);
+  constexpr auto ref = common_reference(Q1::reference, Q2::reference);
   using ret = quantity<ref, decltype(lhs.number() - rhs.number())>;
   return ret(ret(lhs).number() - ret(rhs).number());
 }
@@ -528,7 +528,7 @@ template<Quantity Q1, Quantity Q2>
           std::three_way_comparable_with<typename Q1::rep, typename Q2::rep>
 [[nodiscard]] constexpr auto operator<=>(const Q1& lhs, const Q2& rhs)
 {
-  constexpr auto ref = detail::common_reference(Q1::reference, Q2::reference);
+  constexpr auto ref = common_reference(Q1::reference, Q2::reference);
   return quantity_cast<ref>(lhs).number() <=> quantity_cast<ref>(rhs).number();
 }
 
@@ -537,7 +537,7 @@ template<Quantity Q1, Quantity Q2>
           std::equality_comparable_with<typename Q1::rep, typename Q2::rep>
 [[nodiscard]] constexpr bool operator==(const Q1& lhs, const Q2& rhs)
 {
-  constexpr auto ref = detail::common_reference(Q1::reference, Q2::reference);
+  constexpr auto ref = common_reference(Q1::reference, Q2::reference);
   return quantity_cast<ref>(lhs).number() == quantity_cast<ref>(rhs).number();
 }
 
@@ -548,13 +548,13 @@ namespace std {
 template<units::Quantity Q1, units::Quantity Q2>
   requires requires {
     {
-      units::detail::common_reference(Q1::reference, Q2::reference)
+      units::common_reference(Q1::reference, Q2::reference)
     } -> units::Reference;
     typename common_type_t<typename Q1::rep, typename Q2::rep>;
   }
 struct common_type<Q1, Q2> {
 public:
-  using type = units::quantity<units::detail::common_reference(Q1::reference, Q2::reference),
+  using type = units::quantity<units::common_reference(Q1::reference, Q2::reference),
                                common_type_t<typename Q1::rep, typename Q2::rep>>;
 };
 
diff --git a/src/core/include/units/reference.h b/src/core/include/units/reference.h
index 334c335b..31cf14c9 100644
--- a/src/core/include/units/reference.h
+++ b/src/core/include/units/reference.h
@@ -107,20 +107,18 @@ template<Reference R1, Reference R2>
   return interconvertible(R1::dimension, R2::dimension) && interconvertible(R1::unit, R2::unit);
 }
 
-namespace detail {
-
-[[nodiscard]] consteval auto common_reference(Reference auto r1, Reference auto r2)
+[[nodiscard]] consteval auto common_reference(Reference auto r1, Reference auto r2, Reference auto... rest)
   requires requires {
     {
-      common_dimension(r1.dimension, r2.dimension)
+      common_dimension(r1.dimension, r2.dimension, rest.dimension...)
     } -> Dimension;
     {
-      common_unit(r1.unit, r2.unit)
+      common_unit(r1.unit, r2.unit, rest.unit...)
     } -> Unit;
   }
 {
-  return reference<common_dimension(r1.dimension, r2.dimension), common_unit(r1.unit, r2.unit)>{};
+  return reference<common_dimension(r1.dimension, r2.dimension, rest.dimension...),
+                   common_unit(r1.unit, r2.unit, rest.unit...)>{};
 }
 
-}  // namespace detail
 }  // namespace units
diff --git a/src/core/include/units/unit.h b/src/core/include/units/unit.h
index 7a1f99b8..209c9b0c 100644
--- a/src/core/include/units/unit.h
+++ b/src/core/include/units/unit.h
@@ -586,16 +586,46 @@ template<Unit Lhs, Unit Rhs>
          canonical_lhs.mag == canonical_rhs.mag;
 }
 
-
-// Convertible
-template<Unit Lhs, Unit Rhs>
-[[nodiscard]] consteval bool interconvertible(Lhs lhs, Rhs rhs)
+// Interconvertible
+[[nodiscard]] consteval bool interconvertible(Unit auto u1, Unit auto u2)
 {
-  auto canonical_lhs = detail::get_canonical_unit(lhs);
-  auto canonical_rhs = detail::get_canonical_unit(rhs);
+  auto canonical_lhs = detail::get_canonical_unit(u1);
+  auto canonical_rhs = detail::get_canonical_unit(u2);
   return is_same_v<decltype(canonical_lhs.reference_unit), decltype(canonical_rhs.reference_unit)>;
 }
 
+// Common unit
+[[nodiscard]] consteval auto common_unit(Unit auto u) { return u; }
+
+template<Unit U1, Unit U2>
+[[nodiscard]] consteval auto common_unit(U1 u1, U2 u2)
+  requires(interconvertible(u1, u2))
+{
+  if constexpr (U1{} == U2{}) {
+    if constexpr (std::derived_from<U1, U2>)
+      return u1;
+    else
+      return u2;
+  } else {
+    constexpr auto canonical_lhs = detail::get_canonical_unit(U1{});
+    constexpr auto canonical_rhs = detail::get_canonical_unit(U2{});
+
+    if constexpr (is_integral(canonical_lhs.mag / canonical_rhs.mag))
+      return u2;
+    else if constexpr (is_integral(canonical_rhs.mag / canonical_lhs.mag))
+      return u1;
+    else {
+      constexpr auto cm = detail::common_magnitude(canonical_lhs.mag, canonical_rhs.mag);
+      return scaled_unit<cm, std::remove_const_t<decltype(canonical_lhs.reference_unit)>>{};
+    }
+  }
+}
+
+[[nodiscard]] consteval auto common_unit(Unit auto u1, Unit auto u2, Unit auto u3, Unit auto... rest)
+  requires requires { common_unit(common_unit(u1, u2), u3, rest...); }
+{
+  return common_unit(common_unit(u1, u2), u3, rest...);
+}
 
 /**
  * @brief Computes the value of a unit raised to the `Num/Den` power
@@ -814,31 +844,4 @@ template<typename CharT = char, Unit U>
   return buffer;
 }
 
-namespace detail {
-
-template<Unit U1, Unit U2>
-[[nodiscard]] consteval auto common_unit(U1 u1, U2 u2)
-  requires(interconvertible(u1, u2))
-{
-  if constexpr (U1{} == U2{}) {
-    if constexpr (std::derived_from<U1, U2>)
-      return u1;
-    else
-      return u2;
-  } else {
-    constexpr auto canonical_lhs = detail::get_canonical_unit(U1{});
-    constexpr auto canonical_rhs = detail::get_canonical_unit(U2{});
-
-    if constexpr (is_integral(canonical_lhs.mag / canonical_rhs.mag))
-      return u2;
-    else if constexpr (is_integral(canonical_rhs.mag / canonical_lhs.mag))
-      return u1;
-    else {
-      constexpr auto cm = common_magnitude(canonical_lhs.mag, canonical_rhs.mag);
-      return scaled_unit<cm, std::remove_const_t<decltype(canonical_lhs.reference_unit)>>{};
-    }
-  }
-}
-
-}  // namespace detail
 }  // namespace units