Line data    Source code

       1           0 : // Distributed under the MIT License.
       2             : // See LICENSE.txt for details.
       3             : 
       4             : #pragma once
       5             : 
       6             : #include <cstddef>
       7             : #include <utility>  // IWYU pragma: keep  // for std::move
       8             : 
       9             : #include "DataStructures/TempBuffer.hpp"
      10             : #include "Utilities/Gsl.hpp"
      11             : #include "Utilities/TMPL.hpp"
      12             : #include "Utilities/TaggedTuple.hpp"
      13             : 
      14             : /*!
      15             :  * \ingroup DataStructuresGroup
      16             :  * A temporary buffer with contents computed on demand.
      17             :  *
      18             :  * When an entry in the buffer is first requested, it is computed by the
      19             :  * `computer` that is passed to the `get_var` function. Subsequent requests just
      20             :  * return the cached value.  The computer can itself request data from the cache
      21             :  * to use in its computations.
      22             :  *
      23             :  * For the cache
      24             :  * \snippet Test_CachedTempBuffer.cpp alias
      25             :  * the function used to compute `Tags::Scalar2<DataType>` is
      26             :  * \snippet Test_CachedTempBuffer.cpp compute_func
      27             :  */
      28             : template <typename... Tags>
      29           1 : class CachedTempBuffer {
      30             :  public:
      31           0 :   using tags_list = tmpl::list<Tags...>;
      32             : 
      33             :   /// Construct the buffer with the given computer.  `size` is passed
      34             :   /// to the underlying `TempBuffer` constructor.
      35           1 :   CachedTempBuffer(const size_t size) : data_(size) {}
      36             : 
      37             :   /// Obtain a value from the buffer, computing it if necessary.
      38             :   template <typename Computer, typename Tag>
      39           1 :   const typename Tag::type& get_var(const Computer& computer, Tag /*meta*/) {
      40             :     static_assert(tmpl::list_contains_v<tmpl::list<Tags...>, Tag>,
      41             :                   "The requested tag is not available. See the template "
      42             :                   "parameters of 'CachedTempBuffer' for the computer type and "
      43             :                   "the available tags, and the template parameter of the "
      44             :                   "'get_var' function for the requested tag.");
      45             :     // This function can't be called "get" because that interferes
      46             :     // with the ADL needed to access data_.
      47             :     if (not get<Computed<Tag>>(computed_flags_)) {
      48             :       computer(make_not_null(&get<Tag>(data_)), make_not_null(this), Tag{});
      49             :       get<Computed<Tag>>(computed_flags_) = true;
      50             :     }
      51             :     return get<Tag>(data_);
      52             :   }
      53             : 
      54             :  private:
      55             :   template <typename Tag>
      56           0 :   struct Computed {
      57           0 :     using type = bool;
      58             :   };
      59             : 
      60           0 :   TempBuffer<tmpl::list<Tags...>> data_;
      61           0 :   tuples::TaggedTuple<Computed<Tags>...> computed_flags_{
      62             :       ((void)Tags{}, false)...};
      63             : };
      64             : 
      65             : /// Instantiate a `CachedTempBuffer` from a typelist instead of a parameter pack
      66             : template <typename Tags>
      67           1 : using cached_temp_buffer_from_typelist = tmpl::wrap<Tags, CachedTempBuffer>;