typetraits.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-GPL-2.0-only-with-PDELab-exception
 
#ifndef DUNE_TYPETREE_TYPETRAITS_HH
#define DUNE_TYPETREE_TYPETRAITS_HH
 
#include <type_traits>
#include <dune/common/typetraits.hh>
 
#include <dune/typetree/treepath.hh>
#include <dune/typetree/nodeinterface.hh>
 
namespace Dune {
 
  // Provide some more C++11 TMP helpers.
  // These should be upstreamed to dune-common ASAP.
 
  template<typename... T>
  struct first_type;
 
  template<typename T0, typename... T>
  struct first_type<T0,T...>
  {
    typedef T0 type;
  };
 
  namespace TypeTree {
 
    template<typename T>
    struct has_node_tag
    {
      struct yes { char dummy[1]; };
      struct no  { char dummy[2]; };
 
      template<typename X>
      static yes test(NodeTag<X> *);
      template<typename X>
      static no  test(...);
 
      constexpr static bool value = sizeof(test<T>(0)) == sizeof(yes);
    };
 
    template<typename T, typename V>
    struct has_node_tag_value
    {
      template<int N>
      struct maybe { char dummy[N+1]; };
      struct yes { char dummy[2]; };
      struct no  { char dummy[1]; };
 
      template<typename X>
      static maybe<std::is_base_of<V, NodeTag<X>>::value>
      test(NodeTag<X> * a);
      template<typename X>
      static no test(...);
 
      constexpr static bool value = sizeof(test<T>(0)) == sizeof(yes);
    };
 
    template<typename T>
    struct has_implementation_tag
    {
      struct yes { char dummy[1]; };
      struct no  { char dummy[2]; };
 
      template<typename X>
      static yes test(ImplementationTag<X> *);
      template<typename X>
      static no  test(...);
 
      constexpr static bool value = sizeof(test<T>(0)) == sizeof(yes);
    };
 
    template<typename T, typename V>
    struct has_implementation_tag_value
    {
      template<int N>
      struct maybe { char dummy[N+1]; };
      struct yes { char dummy[2]; };
      struct no  { char dummy[1]; };
 
      template<typename X>
      static maybe<std::is_base_of<V, ImplementationTag<X>>::value>
      test(ImplementationTag<X> * a);
      template<typename X>
      static no test(...);
 
      constexpr static bool value = sizeof(test<T>(0)) == sizeof(yes);
    };
 
    template<typename>
    struct AlwaysVoid
    {
      typedef void type;
    };
 
 
    template<typename T>
    T* declptr();
 
 
    // Support for lazy evaluation of meta functions. This is required when doing
    // nested tag dispatch without C++11-style typedefs (based on using syntax).
    // The standard struct-based meta functions cause premature evaluation in a
    // context that is not SFINAE-compatible. We thus have to return the meta function
    // without evaluating it, placing that burden on the caller. On the other hand,
    // the lookup will often directly be the target type, so here is some helper code
    // to automatically do the additional evaluation if necessary.
    // Too bad that the new syntax is GCC 4.6+...
 
 
 
    struct meta_function {};
 
    template<typename F>
    struct lazy_evaluate
    {
      typedef typename F::type type;
    };
 
    template<typename F>
    struct lazy_identity
    {
      typedef F type;
    };
 
    template<typename F>
    struct evaluate_if_meta_function
    {
      typedef typename std::conditional<
        std::is_base_of<meta_function,F>::value,
        lazy_evaluate<F>,
        lazy_identity<F>
        >::type::type type;
    };
 
    namespace impl {
 
      // Check if type is a or is derived from one of the tree path types
 
      // Default overload for types not representing a tree path
      constexpr auto isTreePath(void*)
        -> std::false_type
      {
        return std::false_type();
      }
 
      // Overload for instances of HybridTreePath<...>
      template<class... I>
      constexpr auto isTreePath(const HybridTreePath<I...>*)
        -> std::true_type
      {
        return std::true_type();
      }
 
    }
 
    template<class T>
    struct IsTreePath :
      public decltype(impl::isTreePath((typename std::decay<T>::type*)(nullptr)))
    {};
 
    template<class T>
    constexpr auto isTreePath(const T&)
      -> IsTreePath<T>
    {
      return IsTreePath<T>();
    }
 
 
  } // end namespace TypeTree
} // end namespace Dune
 
#endif // DUNE_TYPETREE_TYPETRAITS_HH