measurement example added

example/CMakeLists.txt

@@ -26,3 +26,9 @@ target_link_libraries(example
     PRIVATE
         mp::units
 )
+
+add_executable(measurement measurement.cpp)
+target_link_libraries(measurement
+    PRIVATE
+        mp::units
+)

example/measurement.cpp

@@ -0,0 +1,141 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include <units/dimensions/acceleration.h>
+#include <iostream>
+
+namespace {
+
+  template<typename T, template<typename> typename Trait>
+  concept Satisfies = Trait<T>::value;
+  
+  // root sum of squares
+  template<typename T>
+  T rss(const T& v1, const T& v2)
+  {
+    return std::sqrt(std::pow(v1, 2) + std::pow(v2, 2));
+  }
+
+  template<class T>
+  class measurement {
+  public:
+    using value_type = T;
+
+    measurement() = default;
+
+    constexpr /* explicit */ measurement(const value_type& val, const value_type& err = {}):   // cannot be explicit as `magma` concept requires implicit conversions :-(
+        value_(val), uncertainty_(std::abs(err))
+    {
+    }
+
+    constexpr const value_type& value() const { return value_; }
+    constexpr const value_type& uncertainty() const { return uncertainty_; }
+
+    constexpr value_type relative_uncertainty() const { return uncertainty() / value(); }
+    constexpr value_type lower_bound() const { return value() - uncertainty(); }
+    constexpr value_type upper_bound() const { return value() + uncertainty(); }
+
+    [[nodiscard]] constexpr measurement operator-() const { return measurement(-value(), uncertainty()); }
+
+    [[nodiscard]] friend constexpr measurement operator+(const measurement& lhs, const measurement& rhs)
+    {
+      return measurement(lhs.value() + rhs.value(), rss(lhs.uncertainty(), rhs.uncertainty()));
+    }
+
+    [[nodiscard]] friend constexpr measurement operator-(const measurement& lhs, const measurement& rhs)
+    {
+      return measurement(lhs.value() - rhs.value(), rss(lhs.uncertainty(), rhs.uncertainty()));
+    }
+
+    [[nodiscard]] friend constexpr measurement operator*(const measurement& lhs, const measurement& rhs)
+    {
+      const auto val = lhs.value() * rhs.value();
+      return measurement(val, val * rss(lhs.relative_uncertainty(), rhs.relative_uncertainty()));
+    }
+
+    [[nodiscard]] friend constexpr measurement operator/(const measurement& lhs, const measurement& rhs)
+    {
+      const auto val = lhs.value() / rhs.value();
+      return measurement(val, val * rss(lhs.relative_uncertainty(), rhs.relative_uncertainty()));
+    }
+
+    [[nodiscard]] friend constexpr bool operator==(const measurement& lhs, const measurement& rhs)
+    {
+      return lhs.value()  == rhs.value() && lhs.uncertainty() == rhs.uncertainty();
+    }
+
+    [[nodiscard]] friend constexpr bool operator!=(const measurement& lhs, const measurement& rhs)
+    {
+      return !(lhs == rhs);
+    }
+
+    [[nodiscard]] friend constexpr bool operator<(const measurement& lhs, const measurement& rhs)
+    {
+      return lhs.value() == rhs.value() ? lhs.uncertainty() < rhs.uncertainty() : lhs.value() < rhs.value();
+    }
+
+    [[nodiscard]] friend constexpr bool operator>(const measurement& lhs, const measurement& rhs)
+    {
+      return rhs < lhs;
+    }
+
+    [[nodiscard]] friend constexpr bool operator<=(const measurement& lhs, const measurement& rhs)
+    {
+      return !(rhs < lhs);
+    }
+
+    [[nodiscard]] friend constexpr bool operator>=(const measurement& lhs, const measurement& rhs)
+    {
+      return !(lhs < rhs);
+    }
+
+    friend std::ostream& operator<<(std::ostream& os, const measurement& v)
+    {
+      return os << v.value() << " ± " << v.uncertainty();
+    }
+
+  private:
+    value_type value_{};
+    value_type uncertainty_{};
+  };
+
+  template<units::Unit U>
+  using m_quantity = units::quantity<U, measurement<double>>;
+
+}  // namespace
+
+template<typename T>
+inline constexpr bool units::treat_as_floating_point<measurement<T>> = std::is_floating_point_v<T>;
+
+
+int main()
+{
+  const auto a = m_quantity<units::metre_per_second_sq>(measurement(9.8, 0.1));
+  const auto t = m_quantity<units::second>(measurement(1.2, 0.1));
+
+  units::Velocity AUTO v1 = a * t;
+  m_quantity<units::kilometre_per_hour> v2(v1);
+  std::cout << a << " * " << t << " = " << v1 << " = " << v2 << '\n';
+
+  m_quantity<units::metre> length(measurement(123., 1.));
+  std::cout << "10 * " << length << " = " << 10 * length << '\n';
+}