mp-units/example/measurement.cpp

// The MIT License (MIT)
//
// Copyright (c) 2018 Mateusz Pusz
//
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// of this software and associated documentation files (the "Software"), to deal
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// 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
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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#include <units/physical/si/acceleration.h>
#include <cmath>
#include <iostream>

namespace {

// 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()));
  }

#if __GNUC__ >= 10

  [[nodiscard]] friend constexpr auto operator<=>(const measurement& lhs, const measurement& rhs) = default;

#else

  [[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);
  }

#endif

  friend std::ostream& operator<<(std::ostream& os, const measurement& v)
  {
    return os << v.value() << " ± " << v.uncertainty();
  }

private:
  value_type value_{};
  value_type uncertainty_{};
};

static_assert(units::Scalar<measurement<double>>);

}  // namespace

template<typename T>
inline constexpr bool units::treat_as_floating_point<measurement<T>> = std::is_floating_point_v<T>;

namespace {

void example()
{
  using namespace units;

  const auto a = si::acceleration<si::metre_per_second_sq, measurement<double>>(measurement(9.8, 0.1));
  const auto t = si::time<si::second, measurement<double>>(measurement(1.2, 0.1));

  const Velocity AUTO v1 = a * t;
  std::cout << a << " * " << t << " = " << v1 << " = " << quantity_cast<si::kilometre_per_hour>(v1) << '\n';

  si::length<si::metre, measurement<double>> length(measurement(123., 1.));
  std::cout << "10 * " << length << " = " << 10 * length << '\n';
}

}  // namespace

int main()
{
  try {
    example();
  } catch (const std::exception& ex) {
    std::cerr << "Unhandled std exception caught: " << ex.what() << '\n';
  } catch (...) {
    std::cerr << "Unhandled unknown exception caught\n";
  }
}