traits.h

// Copyright (C) 2024-2026 Joseph P. Dean and Garth N. Wells
// This file is part of DOLFINx (https://www.fenicsproject.org)
//
// SPDX-License-Identifier:    LGPL-3.0-or-later
 
#pragma once
 
#include <basix/mdspan.hpp>
#include <concepts>
#include <cstdint>
#include <dolfinx/common/types.h>
#include <span>
#include <tuple>
#include <type_traits>
 
namespace dolfinx::fem
{
template <class U, class T>
concept DofTransformKernel
    = std::is_invocable_v<U, std::span<T>, std::span<const std::uint32_t>,
                          std::int32_t, int>;

template <typename F>
constexpr bool is_transform_set(const F& fn)
{
  if constexpr (requires { static_cast<bool>(fn); })
    return static_cast<bool>(fn);
  else
    return true;
}

template <class U, class T, class G = dolfinx::scalar_value_t<T>>
concept FEkernel = std::is_invocable_v<U, T*, const T*, const T*, const G*,
                                       const int*, const std::uint8_t*, void*>;

template <class T>
concept MDSpan2
    = std::is_convertible_v<
          std::remove_cvref_t<T>,
          md::mdspan<const std::int32_t, md::dextents<std::size_t, 2>>>
      or std::is_convertible_v<
          std::remove_cvref_t<T>,
          md::mdspan<const std::int32_t, md::dextents<std::size_t, 1>>>;

template <class T>
concept MDSpan2Int32
    = dolfinx::MDSpanRank2<T>
      and std::same_as<typename std::remove_cvref_t<T>::value_type,
                       std::int32_t>;

template <class T, class U>
concept MDSpan2Floating
    = std::floating_point<U> and dolfinx::MDSpanRank2<T>
      and std::same_as<typename std::remove_cvref_t<T>::value_type, U>;

template <class T>
concept DofMapPackBase = requires(const std::remove_cvref_t<T>& t) {
  requires std::tuple_size_v<std::remove_cvref_t<T>> == 3;
  requires MDSpan2Int32<decltype(std::get<0>(t))>;
  { std::get<1>(t) } -> std::convertible_to<int>;
};

template <class T>
concept DofMapPackCells
    = DofMapPackBase<T> and requires(const std::remove_cvref_t<T>& t) {
        { std::get<2>(t)[0] } -> std::convertible_to<std::int32_t>;
      };

template <class T>
concept DofMapPackEntities
    = DofMapPackBase<T> and requires(const std::remove_cvref_t<T>& t) {
        { std::get<2>(t)(0, 0) } -> std::convertible_to<std::int32_t>;
      };

template <class T>
concept DofMapPackFacets
    = DofMapPackBase<T> and requires(const std::remove_cvref_t<T>& t) {
        { std::get<2>(t)(0, 0, 0) } -> std::convertible_to<std::int32_t>;
      };
} // namespace dolfinx::fem