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       1            0 : // Distributed under the MIT License.
       2              : // See LICENSE.txt for details.
       3              : 
       4              : #pragma once
       5              : 
       6              : #include <type_traits>
       7              : 
       8              : #include "Utilities/ProtocolHelpers.hpp"
       9              : 
      10              : /// \brief Protocols for the DataBox
      11            1 : namespace db::protocols {
      12              : 
      13              : /// \brief A DataBox mutator
      14              : ///
      15              : /// A class conforming to this protocol can be used as the template argument for
      16              : /// a call to db::mutate_apply(const gsl::not_null<DataBox<BoxTags>*> box,
      17              : /// Args&&... args).  The conforming class must provide the following:
      18              : ///
      19              : /// - `return_tags`: A type list of tags corresponding to mutable items in the
      20              : ///   DataBox passed to `db::mutate_apply` that may be modified.
      21              : /// - `argument_tags`: A type list of tags corresponding to items in the DataBox
      22              : ///   passed to `db::mutate_apply` that may not be modified.
      23              : /// - `apply`: A static function whose return value is returned by
      24              : ///   `db::mutate_apply`, and that takes as arguments:
      25              : ///      - A `const gsl::not_null<Tag::type*>` for each `Tag` in `return_tags`
      26              : ///      - A `const db::const_item_type<Tag, BoxTags>` for each `Tag` in
      27              : ///        `argument_tags`
      28              : ///      - The additional arguments passed to `db::mutate_apply`
      29              : ///
      30              : ///   Note: use the explicit type whenever possible, not the type aliases.
      31              : ///   `db::const_item_type` will usually be `Tag::type` unless that is a
      32              : ///   `std::unique_ptr<T>`, in which case it will be `T`
      33              : ///
      34              : /// Here is an example for a class conforming to this protocol:
      35              : ///
      36              : /// \snippet DataBox/Examples.hpp mutator_protocol
      37            1 : struct Mutator {
      38              :   template <typename ConformingType>
      39            0 :   struct test {
      40            0 :     using argument_tags = typename ConformingType::argument_tags;
      41            0 :     using return_tags = typename ConformingType::return_tags;
      42              :   };
      43              : };
      44              : }  // namespace db::protocols