concepts.h

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/******************************************************************************
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Embedded Template Library.
https://github.com/ETLCPP/etl
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#ifndef ETL_CONCEPTS_INCLUDED
#define ETL_CONCEPTS_INCLUDED
 
#include "platform.h"
 
#include "type_traits.h"
#include "utility.h"
 
#if ETL_NOT_USING_CPP20 && !defined(ETL_IN_UNIT_TEST)
  #error NOT SUPPORTED FOR BELOW C++20
#endif
 
#if ETL_USING_CPP20
 
  #if ETL_USING_STL
    #include <concepts>
  #endif
 
namespace etl
{
 
  #if ETL_USING_STL
 
  using std::assignable_from;
  using std::common_reference_with;
  using std::common_with;
  using std::convertible_to;
  using std::derived_from;
  using std::floating_point;
  using std::integral;
  using std::same_as;
  using std::signed_integral;
  using std::unsigned_integral;
 
  #else // not ETL_USING_STL
 
  namespace private_concepts
  {
    template <typename T, typename U>
    concept same_as_helper = etl::is_same_v<T, U>;
  }
 
  //***************************************************************************
  template <typename T, typename U>
  concept same_as = private_concepts::same_as_helper<T, U> && private_concepts::same_as_helper<U, T>;
 
  //***************************************************************************
  template <typename Derived, typename Base>
  concept derived_from = etl::is_base_of_v<Base, Derived> && etl::is_convertible_v<const volatile Derived*, const volatile Base*>;
 
  //***************************************************************************
  template <typename From, typename To>
  concept convertible_to = etl::is_convertible_v<From, To> && requires { static_cast<To>(etl::declval<From>()); };
 
  //***************************************************************************
  template < class T, typename U >
  concept common_reference_with = etl::same_as<etl::common_reference_t<T, U>, etl::common_reference_t<U, T> >
                                  && etl::convertible_to<T, etl::common_reference_t<T, U> > && etl::convertible_to<U, etl::common_reference_t<T, U> >;
 
  //***************************************************************************
  template <typename T, typename U>
  concept common_with = etl::same_as<etl::common_type_t<T, U>, etl::common_type_t<U, T> > && requires {
    static_cast<etl::common_type_t<T, U> >(etl::declval<T>());
    static_cast<etl::common_type_t<T, U> >(etl::declval<U>());
  } && etl::common_reference_with< etl::add_lvalue_reference_t<const T>, etl::add_lvalue_reference_t<const U> > && etl::common_reference_with< etl::add_lvalue_reference_t<etl::common_type_t<T, U> >, etl::common_reference_t< etl::add_lvalue_reference_t<const T>, etl::add_lvalue_reference_t<const U> > >;
 
  //***************************************************************************
  template <typename T>
  concept integral = etl::is_integral_v<T>;
 
  //***************************************************************************
  template <typename T>
  concept signed_integral = etl::integral<T> && etl::is_signed_v<T>;
 
  //***************************************************************************
  template <typename T>
  concept unsigned_integral = etl::integral<T> && !etl::signed_integral<T>;
 
  //***************************************************************************
  template <typename T>
  concept floating_point = etl::is_floating_point_v<T>;
 
  //***************************************************************************
  template <typename LHS, typename RHS>
  concept assignable_from =
    etl::is_lvalue_reference_v<LHS> && etl::common_reference_with< const etl::remove_reference_t<LHS>&, const etl::remove_reference_t<RHS>&>
    && requires(LHS lhs, RHS&& rhs) {
         { lhs = etl::forward<RHS>(rhs) } -> etl::same_as<LHS>;
       };
 
  #endif
} // namespace etl
#endif
#endif