From 6dd07002c2058007f27d62628eaab6f442d2819b Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Sat, 29 Sep 2018 18:19:25 -0700
Subject: [PATCH] Unit specific concepts introduced

---
 example/example.cpp              |  6 +++---
 src/include/units/si/frequency.h | 13 +++++++++++++
 src/include/units/si/length.h    | 13 +++++++++++++
 src/include/units/si/time.h      | 13 +++++++++++++
 src/include/units/si/velocity.h  | 13 +++++++++++++
 5 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/example/example.cpp b/example/example.cpp
index 2eb568b7..a29ebd1c 100644
--- a/example/example.cpp
+++ b/example/example.cpp
@@ -25,11 +25,11 @@
 
 using namespace units;
 
-template<Unit U1, typename Rep1, Unit U2, typename Rep2>
-void foo(velocity<U1, Rep1> v, time<U2, Rep2> t)
+template<typename V, typename T>
+  requires Velocity<V> && Time<T>
+void foo(V v, T t)
 {
   const auto distance = v * t;
-
   std::cout << "A car driving " << v.count() << " km/h in a time of " << t.count() << " minutes will pass "
             << quantity_cast<length<meter, int>>(distance).count() << " meters.\n";
 }
diff --git a/src/include/units/si/frequency.h b/src/include/units/si/frequency.h
index ac7731fc..b7d972a5 100644
--- a/src/include/units/si/frequency.h
+++ b/src/include/units/si/frequency.h
@@ -39,6 +39,19 @@ namespace units {
   template<Unit U = hertz, typename Rep = std::intmax_t>
   using frequency = quantity<dimension_frequency, U, Rep>;
 
+  namespace detail {
+
+    template<typename T>
+    struct is_frequency : std::false_type {};
+
+    template<Unit U, typename Rep>
+    struct is_frequency<frequency<U, Rep>> : std::true_type {};
+
+  }
+
+  template<typename T>
+  concept bool Frequency = detail::is_frequency<T>::value;
+
   // ...
 
   namespace literals {
diff --git a/src/include/units/si/length.h b/src/include/units/si/length.h
index 150330df..9487657b 100644
--- a/src/include/units/si/length.h
+++ b/src/include/units/si/length.h
@@ -36,6 +36,19 @@ namespace units {
   template<Unit U = meter, typename Rep = std::intmax_t>
   using length = quantity<dimension_length, U, Rep>;
 
+  namespace detail {
+
+    template<typename T>
+    struct is_length : std::false_type {};
+
+    template<Unit U, typename Rep>
+    struct is_length<length<U, Rep>> : std::true_type {};
+
+  }
+
+  template<typename T>
+  concept bool Length = detail::is_length<T>::value;
+
   namespace literals {
 
     // mm
diff --git a/src/include/units/si/time.h b/src/include/units/si/time.h
index d32c0160..de7f1955 100644
--- a/src/include/units/si/time.h
+++ b/src/include/units/si/time.h
@@ -39,6 +39,19 @@ namespace units {
   template<Unit U = second, typename Rep = std::intmax_t>
   using time = quantity<dimension_time, U, Rep>;
 
+  namespace detail {
+
+    template<typename T>
+    struct is_time : std::false_type {};
+
+    template<Unit U, typename Rep>
+    struct is_time<time<U, Rep>> : std::true_type {};
+
+  }
+
+  template<typename T>
+  concept bool Time = detail::is_time<T>::value;
+
   // ...
 
   namespace literals {
diff --git a/src/include/units/si/velocity.h b/src/include/units/si/velocity.h
index 6b6b917e..3d153b8e 100644
--- a/src/include/units/si/velocity.h
+++ b/src/include/units/si/velocity.h
@@ -37,6 +37,19 @@ namespace units {
   template<Unit U = meter_per_second, typename Rep = std::intmax_t>
   using velocity = quantity<dimension_velocity, U, Rep>;
 
+  namespace detail {
+
+    template<typename T>
+    struct is_velocity : std::false_type {};
+
+    template<Unit U, typename Rep>
+    struct is_velocity<velocity<U, Rep>> : std::true_type {};
+
+  }
+
+  template<typename T>
+  concept bool Velocity = detail::is_velocity<T>::value;
+
   // ...
 
   namespace literals {