pTraits.H

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/*---------------------------------------------------------------------------*\
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    Copyright (C) 2011 OpenFOAM Foundation
    Copyright (C) 2020-2023 OpenCFD Ltd.
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

Class
    Foam::pTraits

Description
    A traits class, which is primarily used for primitives and vector-space.

    All primitives need a specialised version of this class. The
    specialised versions will normally also require a conversion
    method.

\*---------------------------------------------------------------------------*/

#ifndef Foam_pTraits_H
#define Foam_pTraits_H

#include "direction.H"
#include <type_traits>  // For std::integral_constant, std::void_t (C++17)
#include <utility>      // For declval

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace stdFoam
{

//- Map a sequence of any types to \c void as per C++17 \c std::void_t
template<class... >
using void_t = void;

} // End namespace stdFoam


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace Foam
{

/*---------------------------------------------------------------------------*\
                          Class zero_one Declaration
\*---------------------------------------------------------------------------*/

//- Represents 0/1 range or concept. Used for tagged dispatch or clamping
class zero_one {};


/*---------------------------------------------------------------------------*\
                           Class pTraits Declaration
\*---------------------------------------------------------------------------*/

// The base implementation is a pass-through to the base class.
// Accordingly it inherits all static methods (eg, typeName etc).
template<class Base>
class pTraits
:
    public Base
{
public:

    // Constructors

        //- Copy construct from base class
        explicit pTraits(const Base& obj)
        :
            Base(obj)
        {}

        //- Construct from Istream
        explicit pTraits(Istream& is)
        :
            Base(is)
        {}
};


/*---------------------------------------------------------------------------*\
                              VectorSpace Traits
\*---------------------------------------------------------------------------*/

//- Test for VectorSpace : default is false
template<class T, class = void>
struct is_vectorspace : std::false_type {};

//- Test for VectorSpace : test for T::rank != 0 static member directly
//  Do not need pTraits layer since rank is defined via VectorSpace etc
template<class T>
struct is_vectorspace<T, stdFoam::void_t<decltype(T::rank)>>
:
    std::integral_constant<bool, (T::rank != 0)>
{};


//- The vector-space rank: default is 0.
template<class T, class = void>
struct pTraits_rank : std::integral_constant<Foam::direction, 0> {};

//- Rank of VectorSpace,
//- using the pTraits \c rank static member.
template<class T>
struct pTraits_rank
<
    T,
    stdFoam::void_t<decltype(pTraits<T>::rank)>
>
:
    std::integral_constant<Foam::direction, pTraits<T>::rank>
{};


//- The underlying component data type: default is pass-through.
template<class T, class = void>
struct pTraits_cmptType { typedef T type; };

//- The underlying component data type for vector-space (or complex).
//  Enabled when pTraits<T>:zero has a defined type (ie, exists),
//  such as for arithmetic primitives, vector-space etc. where the concept
//  of a component type also makes sense.
template<class T>
struct pTraits_cmptType<T, stdFoam::void_t<decltype(pTraits<T>::zero)>>
{
    typedef typename pTraits<T>::cmptType type;
};


//- The vector-space number of components: default is 1.
template<class T, class = void>
struct pTraits_nComponents : std::integral_constant<Foam::direction, 1> {};

//- Number of VectorSpace components,
//- using the pTraits \c nComponents static member.
template<class T>
struct pTraits_nComponents
<
    T,
    stdFoam::void_t<decltype(pTraits<T>::nComponents)>
>
:
    std::integral_constant<Foam::direction, pTraits<T>::nComponents>
{};


//- Test for pTraits zero : default is false
template<class T, class = void>
struct pTraits_has_zero : std::false_type {};

//- Test for pTraits zero
template<class T>
struct pTraits_has_zero
<
    T,
    stdFoam::void_t<decltype(pTraits<T>::zero)>
>
:
    std::true_type
{};


/*---------------------------------------------------------------------------*\
                               Container Traits
\*---------------------------------------------------------------------------*/

//- Test for containers with begin/end range iterators.
template<class T, class = void>
struct is_range : std::false_type {};

//- Test for list containers with begin/end range iterators.
//- \attention May yield a false positive with HashTable, HashSet etc
template<class T>
struct is_range
<
    T,
    stdFoam::void_t
    <
        decltype(std::declval<T>().begin()),
        decltype(std::declval<T>().end())
    >
>
:
    std::true_type
{};


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

} // End namespace Foam

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#endif

// ************************************************************************* //