signature.hh

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
 
// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file AUTHORS.md
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception OR LGPL-3.0-or-later
 
#ifndef DUNE_FUNCTIONS_COMMON_SIGNATURE_HH
#define DUNE_FUNCTIONS_COMMON_SIGNATURE_HH
 
#include <type_traits>
#include <tuple>
 
#include <dune/functions/common/defaultderivativetraits.hh>
 
namespace Dune {
namespace Functions {
 
template<typename F>
struct IsCallable;
 
#ifndef DOXYGEN
template<typename F>
struct IsCallable
{
    struct yes { std::size_t dummy[2]; };
    struct no  { std::size_t dummy[1]; };
 
    template<typename C>
    static yes test(const decltype(&C::operator()) *);
    template<typename C>
    static no  test(...);
 
    enum { value = (sizeof(test<F>(0)) == sizeof(yes)) };
};
 
template<typename R, typename D>
struct IsCallable<R(D)>
{
    enum { value = true };
};
 
template<typename R, typename D>
struct IsCallable<R(*)(D)>
{
    enum { value = true };
};
#endif
 
template<class Signature, bool isCallable = IsCallable<Signature>::value >
struct SignatureTraits {};
 
#ifndef DOXYGEN
template<class T>
struct SignatureTraits<T, true>
    : public SignatureTraits<decltype(&T::operator()), true>
{};
 
template <typename C, typename R, typename D>
struct SignatureTraits<R(C::*)(D) const, true>
    : public SignatureTraits<R(D), true>
{};
 
template <typename C, typename R, typename D>
struct SignatureTraits<R(C::*)(D), true>
    : public SignatureTraits<R(D), true>
{};
 
template <typename R, typename D>
struct SignatureTraits<R(*)(D), true>
    : public SignatureTraits<R(D), true>
{};
 
template<class R, class D>
struct SignatureTraits<R(D), true>
{
    using Range = R;
    using Domain = D;
 
    using RawRange = std::decay_t<Range>;
    using RawDomain = std::decay_t<Domain>;
 
    using RawSignature = RawRange(RawDomain);
 
    template<template<class> class DerivativeTraits=DefaultDerivativeTraits>
    using DerivativeSignature = typename DerivativeTraits<RawSignature>::Range(Domain);
};
#endif
 
 
template<class Signature, template<class> class DerivativeTraits=DefaultDerivativeTraits>
struct SignatureTag;
 
template<class Range, class Domain, template<class> class DerivativeTraitsT>
struct SignatureTag<Range(Domain), DerivativeTraitsT>
{
  using Signature = Range(Domain);
 
  template<class T>
  using DerivativeTraits = DerivativeTraitsT<T>;
};
 
 
 
template<class Range, class Domain, template<class> class DerivativeTraits>
auto derivativeSignatureTag(SignatureTag<Range(Domain), DerivativeTraits> tag)
{
  using DerivativeRange = typename DerivativeTraits<Range(Domain)>::Range;
  return SignatureTag<DerivativeRange(Domain), DerivativeTraits>();
}
 
 
 
template<std::size_t maxOrder, class Signature, template<class> class DerivativeTraits>
auto derivativeSignatureTags(Dune::Functions::SignatureTag<Signature, DerivativeTraits> tag)
{
  if constexpr (maxOrder==0) {
    // If maxOrder== 0 we just need the given SignatureTag
    return std::make_tuple(tag);
  } else {
    // else we first construct the tail tuple with SignatureTags for derivatives
    // of order 1 to maxOrder
    auto tailTagsTuple = derivativeSignatureTags<std::size_t(maxOrder-1)>(derivativeSignatureTag(tag));
    // and prepend this with the given SignatureTag.
    // This is done by unpacking the tail tuple with apply().
    return std::apply([&](auto&&... tailTags){
      return std::make_tuple(tag, tailTags...);
    }, tailTagsTuple);
  }
}
 
 
 
} // namespace Functions
} // namespace Dune
 
#endif // DUNE_FUNCTIONS_COMMON_SIGNATURE_HH