array_adapter.hpp

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// Copyright (c) 2020-2023 Simons Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0.txt
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Olivier Parcollet, Nils Wentzell
 
/**
 * @file
 * @brief Provides an array adapter class.
 */
 
#pragma once
 
#include "./concepts.hpp"
#include "./stdutil/array.hpp"
 
#include <array>
#include <type_traits>
 
namespace nda {
 
  /**
   * @addtogroup av_utils
   * @{
   */
 
  /**
   * @brief Adapter that consists of a shape and a callable object, which takes `R` integers as arguments (just like an
   * nda::basic_array or nda::basic_array_view).
   *
   * @tparam R Rank of the adapter.
   * @tparam F Callable type.
   */
  template <int R, typename F>
  class array_adapter {
    static_assert(CallableWithLongs<F, R>, "Error in nda::array_adapter: Lambda should be callable with R integers");
 
    // Shape of the array.
    std::array<long, R> myshape;
 
    // Callable object.
    F f;
 
    public:
    /**
     * @brief Construct a new array adapter object.
     *
     * @tparam Int Integer type.
     * @param shape Shape of the adapater.
     * @param f Callable object.
     */
    template <typename Int>
    array_adapter(std::array<Int, R> const &shape, F f) : myshape(stdutil::make_std_array<long>(shape)), f(f) {}
 
    /**
     * @brief Get shape of the adapter.
     * @return `std::array<long, R>` object specifying the shape of the adapter.
     */
    [[nodiscard]] auto const &shape() const { return myshape; }
 
    /**
     * @brief Get the total size of the adapter.
     * @return Number of elements in the adapter.
     */
    [[nodiscard]] long size() const { return stdutil::product(myshape); }
 
    /**
     * @brief Function call operator simply forwards the arguments to the callable object.
     *
     * @tparam Ints Integer types (convertible to long).
     * @param i0 First argument.
     * @param is Rest of the arguments.
     */
    template <typename... Ints>
    auto operator()(long i0, Ints... is) const {
      static_assert((std::is_convertible_v<Ints, long> and ...), "Error in nda::array_adapter: Arguments must be convertible to long");
      return f(i0, is...);
    }
  };
 
  // Class template argument deduction guides.
  template <auto R, typename Int, typename F>
  array_adapter(std::array<Int, R>, F) -> array_adapter<R, F>;
 
  /** @} */
 
  /**
   * @ingroup utils_type_traits
   * @brief Specialization of nda::get_algebra for nda::array_adapter.
   */
  template <int R, typename F>
  inline constexpr char get_algebra<array_adapter<R, F>> = 'A';
 
} // namespace nda