mp-units/src/core/include/units/customization_points.h

// The MIT License (MIT)
//
// Copyright (c) 2018 Mateusz Pusz
//
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#pragma once

#include <units/bits/external/hacks.h>
#include <limits>
#include <type_traits>

namespace units {

/**
 * @brief Specifies if a value of a type should be treated as a floating-point value
 *
 * This type trait should be specialized for a custom representation type to specify
 * that values fo this type should be treated by the library as a floating-point ones
 * which will enable implicit conversions between quantities.
 *
 * @tparam Rep a representation type for which a type trait is defined
 */
template<typename Rep>
inline constexpr bool treat_as_floating_point = std::is_floating_point_v<Rep>;

template<typename T>
  requires requires { typename T::value_type; }
inline constexpr bool treat_as_floating_point<T> = treat_as_floating_point<typename T::value_type>;

/**
 * @brief A type trait that defines zero, one, min, and max for a representation type
 *
 * The zero, one, min, and max member functions in units::quantity forward their work to
 * these methods. This type can be specialized if the representation Rep requires a specific
 * implementation to return these quantity objects.
 *
 * @tparam Rep a representation type for which a type trait is defined
 */
template<typename Rep>
struct quantity_values {
  static constexpr Rep zero() noexcept
    requires std::constructible_from<Rep, int>
  {
    return Rep(0);
  }

  static constexpr Rep one() noexcept
    requires std::constructible_from<Rep, int>
  {
    return Rep(1);
  }

  static constexpr Rep min() noexcept
    requires requires {
               {
                 std::numeric_limits<Rep>::lowest()
                 } -> std::same_as<Rep>;
             }
  {
    return std::numeric_limits<Rep>::lowest();
  }

  static constexpr Rep max() noexcept
    requires requires {
               {
                 std::numeric_limits<Rep>::max()
                 } -> std::same_as<Rep>;
             }
  {
    return std::numeric_limits<Rep>::max();
  }
};

/**
 * @brief Provides support for external quantity-like types
 *
 * The type trait should provide the following nested type aliases: @c dimension, @c unit, @c rep,
 * and a static member function @c number(T) that will return the raw value of the quantity.
 *
 * Usage example can be found in @c units/chrono.h header file.
 *
 * @tparam T the type to provide support for
 */
template<typename T>
struct quantity_like_traits;

/**
 * @brief Provides support for external quantity point-like types
 *
 * The type trait should provide the following nested type aliases: @c origin, @c unit, @c rep,
 * and a static member function @c relative(T) that will return the quantity-like value of the quantity point.
 *
 * Usage example can be found in @c units/chrono.h header file.
 *
 * @tparam T the type to provide support for
 */
template<typename T>
struct quantity_point_like_traits;

}  // namespace units