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:
#ifndef DUNE_TYPETRAITS_HH
#define DUNE_TYPETRAITS_HH
 
#include <complex>
#include <type_traits>
#include <utility>
 
#include <dune/common/deprecated.hh>
 
namespace Dune
{
 
  namespace Impl
  {
 
    template <class...>
    struct voider
    {
      using type = void;
    };
  }
 
 
  template <class... Types>
  using void_t = typename Impl::voider<Types...>::type;
 
  struct Empty {};
 
  template<class T1, class T2>
  struct IsInteroperable
  {
    enum {
      value = std::is_convertible<T1,T2>::value || std::is_convertible<T2,T1>::value
    };
  };
 
  template<class T1, class T2, class Type>
  struct EnableIfInterOperable
    : public std::enable_if<IsInteroperable<T1,T2>::value, Type>
  {};
 
 
 
  template<typename T>
  struct AlwaysFalse {
    static const bool value = false;
  };
 
  template<typename T>
  struct AlwaysTrue {
    static const bool value = true;
  };
 
 
  template <typename T>
  struct IsNumber
    : public std::integral_constant<bool, std::is_arithmetic<T>::value> {
  };
 
#ifndef DOXYGEN
 
  template <typename T>
  struct IsNumber<std::complex<T>>
    : public std::integral_constant<bool, IsNumber<T>::value> {
  };
 
#endif // DOXYGEN
 
 
 
  template <typename T>
  struct has_nan
      : public std::integral_constant<bool, std::is_floating_point<T>::value> {
  };
 
#ifndef DOXYGEN
 
  template <typename T>
  struct has_nan<std::complex<T>>
      : public std::integral_constant<bool, std::is_floating_point<T>::value> {
  };
 
#endif // DOXYGEN
 
 
#if defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
 
#ifndef DOXYGEN
 
  namespace Impl {
 
    template<typename T, typename I, typename = int>
    struct _is_indexable
      : public std::false_type
    {};
 
    template<typename T, typename I>
    struct _is_indexable<T,I,typename std::enable_if<(sizeof(std::declval<T>()[std::declval<I>()]) > 0),int>::type>
      : public std::true_type
    {};
 
  }
 
#endif // DOXYGEN
 
 
  template<typename T, typename I = std::size_t>
  struct is_indexable
    : public Impl::_is_indexable<T,I>
  {};
 
 
#else // defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
 
 
  // okay, here follows a mess of compiler bug workarounds...
  // GCC 4.4 dies if we try to subscript a simple type like int and
  // both GCC 4.4 and 4.5 don't like using arbitrary types as subscripts
  // for macros.
  // So we make sure to only ever attempt the SFINAE for operator[] for
  // class types, and to make sure the compiler doesn't become overly eager
  // we have to do some lazy evaluation tricks with nested templates and
  // stuff.
  // Let's get rid of GCC 4.4 ASAP!
 
 
  namespace Impl {
 
    // simple wrapper template to support the lazy evaluation required
    // in _is_indexable
    template<typename T>
    struct _lazy
    {
      template<typename U>
      struct evaluate
      {
        typedef T type;
      };
    };
 
    // default version, gets picked if SFINAE fails
    template<typename T, typename = int>
    struct _is_indexable
      : public std::false_type
    {};
 
    // version for types supporting the subscript operation
    template<typename T>
    struct _is_indexable<T,decltype(std::declval<T>()[0],0)>
      : public std::true_type
    {};
 
    // helper struct for delaying the evaluation until we are sure
    // that T is a class (i.e. until we are outside std::conditional
    // below)
    struct _check_for_index_operator
    {
 
      template<typename T>
      struct evaluate
        : public _is_indexable<T>
      {};
 
    };
 
  }
 
  // The rationale here is as follows:
  // 1) If we have an array, we assume we can index into it. That isn't
  //    true if I isn't an integral type, but that's why we have the static assertion
  //    in the body - we could of course try and check whether I is integral, but I
  //    can't be arsed and want to provide a motivation to switch to a newer compiler...
  // 2) If we have a class, we use SFINAE to check for operator[]
  // 3) Otherwise, we assume that T does not support indexing
  //
  // In order to make sure that the compiler doesn't accidentally try the SFINAE evaluation
  // on an array or a scalar, we have to resort to lazy evaluation.
  template<typename T, typename I = std::size_t>
  struct is_indexable
    : public std::conditional<
               std::is_array<T>::value,
               Impl::_lazy<std::true_type>,
               typename std::conditional<
                 std::is_class<T>::value,
                 Impl::_check_for_index_operator,
                 Impl::_lazy<std::false_type>
                 >::type
               >::type::template evaluate<T>::type
  {
    static_assert(std::is_same<I,std::size_t>::value,"Your compiler is broken and does not support checking for arbitrary index types");
  };
 
 
#endif // defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
 
#ifndef DOXYGEN
 
  namespace Impl {
    // This function does nothing.
    // By passing expressions to this function one can avoid
    // "value computed is not used" warnings that may show up
    // in a comma expression.
    template<class...T>
    void ignore(T&&... /*t*/)
    {}
  }
 
#endif // DOXYGEN
 
  // default version, gets picked if SFINAE fails
  template<typename T, typename = void>
  struct is_range
    : public std::false_type
  {};
 
#ifndef DOXYGEN
  // version for types with begin() and end()
  template<typename T>
  struct is_range<T, decltype(Impl::ignore(
      std::declval<T>().begin(),
      std::declval<T>().end(),
      std::declval<T>().begin() != std::declval<T>().end(),
      decltype(std::declval<T>().begin()){std::declval<T>().end()},
      ++(std::declval<std::add_lvalue_reference_t<decltype(std::declval<T>().begin())>>()),
      *(std::declval<T>().begin())
      ))>
    : public std::true_type
  {};
#endif
 
#ifndef DOXYGEN
  // this is just a forward declaration
  template <class> struct FieldTraits;
#endif
 
  template <class Type>
  using field_t = typename FieldTraits<Type>::field_type;
 
  template <class Type>
  using real_t = typename FieldTraits<Type>::real_type;
 
 
#ifndef DOXYGEN
 
  // Implementation of IsTuple
  namespace Impl {
 
  template<class T>
  struct IsTuple : public std::false_type
  {};
 
  template<class... T>
  struct IsTuple<std::tuple<T...>> : public std::true_type
  {};
 
  } // namespace Impl
 
#endif // DOXYGEN
 
  template<class T>
  struct IsTuple :
    public Impl::IsTuple<T>
  {};
 
 
#ifndef DOXYGEN
 
  // Implementation of IsTupleOrDerived
  namespace Impl {
 
  template<class... T, class Dummy>
  std::true_type isTupleOrDerived(const std::tuple<T...>*, Dummy)
  { return {}; }
 
  template<class Dummy>
  std::false_type isTupleOrDerived(const void*, Dummy)
  { return {}; }
 
  } // namespace Impl
 
#endif // DOXYGEN
 
  template<class T>
  struct IsTupleOrDerived :
    public decltype(Impl::isTupleOrDerived(std::declval<T*>(), true))
  {};
 
 
#ifndef DOXYGEN
 
  // Implementation of is IsIntegralConstant
  namespace Impl {
 
  template<class T>
  struct IsIntegralConstant : public std::false_type
  {};
 
  template<class T, T t>
  struct IsIntegralConstant<std::integral_constant<T, t>> : public std::true_type
  {};
 
  } // namespace Impl
 
#endif // DOXYGEN
 
  template<class T>
  struct IsIntegralConstant : public Impl::IsIntegralConstant<std::decay_t<T>>
  {};
 
 
 
  template<typename... T>
  struct SizeOf
    : public std::integral_constant<std::size_t,sizeof...(T)>
  {};
 
 
#ifndef DOXYGEN
 
  namespace Impl {
 
  template<class T, T...>
  struct IntegerSequenceHelper;
 
  // Helper struct to compute the i-th entry of a std::integer_sequence
  //
  // This could also be implemented using std::get<index>(std::make_tuple(t...)).
  // However, the gcc-6 implementation of std::make_tuple increases the instantiation
  // depth by 15 levels for each argument, such that the maximal instantiation depth
  // is easily hit, especially with clang where it is set to 256.
  template<class T, T head, T... tail>
  struct IntegerSequenceHelper<T, head, tail...>
  {
 
    // get first entry
    static constexpr auto get(std::integral_constant<std::size_t, 0>)
    {
      return std::integral_constant<T, head>();
    }
 
    // call get with first entry cut off and decremented index
    template<std::size_t index,
      std::enable_if_t<(index > 0) and (index < sizeof...(tail)+1), int> = 0>
    static constexpr auto get(std::integral_constant<std::size_t, index>)
    {
      return IntegerSequenceHelper<T, tail...>::get(std::integral_constant<std::size_t, index-1>());
    }
 
    // use static assertion if index exceeds size
    template<std::size_t index,
      std::enable_if_t<(index >= sizeof...(tail)+1), int> = 0>
    static constexpr auto get(std::integral_constant<std::size_t, index>)
    {
      static_assert(index < sizeof...(tail)+1, "index used in IntegerSequenceEntry exceed size");
    }
  };
 
  } // end namespace Impl
 
#endif // DOXYGEN
 
 
  template<class T, T... t, std::size_t index>
  constexpr auto integerSequenceEntry(std::integer_sequence<T, t...> /*seq*/, std::integral_constant<std::size_t, index> i)
  {
    static_assert(index < sizeof...(t), "index used in IntegerSequenceEntry exceed size");
    return Impl::IntegerSequenceHelper<T, t...>::get(i);
  }
 
 
  template<class IntegerSequence, std::size_t index>
  struct IntegerSequenceEntry;
 
#ifndef DOXYGEN
 
  template<class T, T... t, std::size_t i>
  struct IntegerSequenceEntry<std::integer_sequence<T, t...>, i>
    : public decltype(Impl::IntegerSequenceHelper<T, t...>::get(std::integral_constant<std::size_t, i>()))
  {};
 
#endif // DOXYGEN
 
}
#endif