MutateAssign.hpp

// Distributed under the MIT License.
// See LICENSE.txt for details.
 
#pragma once
 
#include <utility>
 
#include "DataStructures/DataBox/DataBox.hpp"
#include "Utilities/Gsl.hpp"
#include "Utilities/TMPL.hpp"
 
namespace Initialization {
namespace detail {
template <typename... MutateTags, typename BoxTags, typename... Args>
SPECTRE_ALWAYS_INLINE constexpr void mutate_assign_impl(
    // NOLINTNEXTLINE(readability-avoid-const-params-in-decls)
    const gsl::not_null<db::DataBox<BoxTags>*> box,
    tmpl::list<MutateTags...> /*meta*/, Args&&... args) noexcept {
  static_assert(sizeof...(MutateTags) == sizeof...(args),
                "The number of arguments passed to `mutate_assign` must be "
                "equal to the number of tags passed.");
  // NOLINTNEXTLINE(modernize-avoid-c-arrays)
  db::mutate<MutateTags...>(box, [&args...](const auto... box_args) noexcept {
    // silence unused capture warnings when there are zero args.
    // This function still gets instantiated despite the `static_assert` in the
    // parent function.
    EXPAND_PACK_LEFT_TO_RIGHT((void)args);
    // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-array-to-pointer-decay)
    EXPAND_PACK_LEFT_TO_RIGHT((*box_args = std::forward<Args>(args)));
  });
}
}  // namespace detail
 
/*!
 * \ingroup DataBoxGroup
 * \brief Perform a mutation to the \ref DataBoxGroup `box`, assigning the
 * `args` to the tags in `MutateTagList` in order.
 */
template <typename MutateTagList, typename BoxTags, typename... Args>
SPECTRE_ALWAYS_INLINE constexpr void mutate_assign(
    // NOLINTNEXTLINE(readability-avoid-const-params-in-decls)
    const gsl::not_null<db::DataBox<BoxTags>*> box, Args&&... args) noexcept {
  static_assert(
      tmpl::size<MutateTagList>::value > 0,
      "At least one tag must be passed to `Initialization::mutate_assign`, but "
      "received 0 tags to mutate.");
  detail::mutate_assign_impl(box, MutateTagList{}, std::forward<Args>(args)...);
}
}  // namespace Initialization