hashable.hh

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// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
#ifndef DUNE_COMMON_CONCEPTS_HASHABLE_HH
#define DUNE_COMMON_CONCEPTS_HASHABLE_HH

// check whether c++20 concept can be used
#if __has_include(<version>) && __has_include(<concepts>)
  #include <version>
  #if  __cpp_concepts >= 201907L && __cpp_lib_concepts >= 202002L
    #ifndef DUNE_ENABLE_CONCEPTS
    #define DUNE_ENABLE_CONCEPTS 1
    #endif
  #endif
#endif

#if DUNE_ENABLE_CONCEPTS

#include <concepts>
#include <cstddef>
#include <functional>

namespace Dune::Concept {

template<class T>
concept Hashable = requires(T a)
{
  { std::hash<T>{}(a) } -> std::convertible_to<std::size_t>;
};

} // end namespace Dune::Concept

#endif // DUNE_ENABLE_CONCEPTS

#endif // DUNE_COMMON_CONCEPTS_HASHABLE_HH