text: /*******************************<GINKGO LICENSE>******************************
  Copyright (c) 2017-2020, the Ginkgo authors
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  
  1. Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.
  
  2. Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.
  
  3. Neither the name of the copyright holder nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  ******************************<GINKGO LICENSE>*******************************/
  
  #ifndef GKO_CORE_BASE_ABSTRACT_FACTORY_HPP_
  #define GKO_CORE_BASE_ABSTRACT_FACTORY_HPP_
  
  
  #include <ginkgo/core/base/polymorphic_object.hpp>
  
  
  /**
   * @brief The Ginkgo namespace.
   *
   * @ingroup gko
   */
  namespace gko {
  
  
  /**
   * The AbstractFactory is a generic interface template that enables easy
   * implementation of the abstract factory design pattern.
   *
   * The interface provides the AbstractFactory::generate() method that can
   * produce products of type `AbstractProductType` using an object of
   * `ComponentsType` (which can be constructed on the fly from parameters to its
   * constructors).
   * The generate() method is not declared as virtual, as this allows subclasses
   * to hide the method with a variant that preserves the compile-time type of the
   * objects. Instead, implementers should override the generate_impl() method,
   * which is declared virtual.
   *
   * Implementers of concrete factories should consider using the
   * EnableDefaultFactory mixin to obtain default implementations of utility
   * methods of PolymorphicObject and AbstractFactory.
   *
   * @tparam AbstractProductType  the type of products the factory produces
   * @tparam ComponentsType  the type of components the factory needs to produce
   *                         the product
   */
  template <typename AbstractProductType, typename ComponentsType>
  class AbstractFactory
      : public EnableAbstractPolymorphicObject<
            AbstractFactory<AbstractProductType, ComponentsType>> {
  public:
      using abstract_product_type = AbstractProductType;
      using components_type = ComponentsType;
  
      /**
       * Creates a new product from the given components.
       *
       * The method will create an ComponentsType object from the arguments of
       * this method, and pass it to the generate_impl() function which will
       * create a new AbstractProductType.
       *
       * @tparam Args  types of arguments passed to the constructor of
       *               ComponentsType
       *
       * @param args  arguments passed to the constructor of ComponentsType
       *
       * @return an instance of AbstractProductType
       */
      template <typename... Args>
      std::unique_ptr<AbstractProductType> generate(Args &&... args) const
      {
          auto product = this->generate_impl({std::forward<Args>(args)...});
          for (auto logger : this->loggers_) {
              product->add_logger(logger);
          }
          return product;
      }
  
  protected:
      /**
       * Constructs a new factory on the specified executor.
       *
       * @param exec  the executor where the factory should be constructed
       */
      AbstractFactory(std::shared_ptr<const Executor> exec)
          : EnableAbstractPolymorphicObject<AbstractFactory>(std::move(exec))
      {}
  
      /**
       * Constructs a new product from the given components.
       *
       * @param args  the components from which to create the product
       *
       * @return an instance of AbstractProductType
       */
      virtual std::unique_ptr<AbstractProductType> generate_impl(
          ComponentsType args) const = 0;
  };
  
  
  /**
   * This mixin provides a default implementation of a concrete factory.
   *
   * It implements all the methods of AbstractFactory and PolymorphicObject.
   * Its implementation of the generate_impl() method delegates the creation of
   * the product by calling the
   * `ProductType::ProductType(const ConcreteFactory *, const components_type &)`
   * constructor. The factory also supports parameters by using the
   * `ParametersType` structure, which is defined by the user.
   *
   * For a simple example, see IntFactory in
   * `core/test/base/abstract_factory.cpp`.
   *
   * @tparam ConcreteFactory  the concrete factory which is being implemented
   *                          [CRTP parameter]
   * @tparam ProductType  the concrete type of products which this factory
   *                      produces, has to be a subclass of
   *                      PolymorphicBase::abstract_product_type
   * @tparam ParametersType  a type representing the parameters of the factory,
   *                         has to inherit from the enable_parameters_type mixin
   * @tparam PolymorphicBase  parent of ConcreteFactory in the polymorphic
   *                          hierarchy, has to be a subclass of AbstractFactory
   */
  template <typename ConcreteFactory, typename ProductType,
            typename ParametersType, typename PolymorphicBase>
  class EnableDefaultFactory
      : public EnablePolymorphicObject<ConcreteFactory, PolymorphicBase>,
        public EnablePolymorphicAssignment<ConcreteFactory> {
  public:
      friend class EnablePolymorphicObject<ConcreteFactory, PolymorphicBase>;
  
      using product_type = ProductType;
      using parameters_type = ParametersType;
      using polymorphic_base = PolymorphicBase;
      using abstract_product_type =
          typename PolymorphicBase::abstract_product_type;
      using components_type = typename PolymorphicBase::components_type;
  
      template <typename... Args>
      std::unique_ptr<ProductType> generate(Args &&... args) const
      {
          auto product = std::unique_ptr<ProductType>(static_cast<ProductType *>(
              this->generate_impl({std::forward<Args>(args)...}).release()));
          propagate_loggers<ConcreteFactory, ProductType>(product.get());
          return product;
      }
  
      /**
       * Returns the parameters of the factory.
       *
       * @return the parameters of the factory
       */
      const parameters_type &get_parameters() const noexcept
      {
          return parameters_;
      };
  
      /**
       * Creates a new ParametersType object which can be used to instantiate a
       * new ConcreteFactory.
       *
       * This method does not construct the factory directly, but returns a new
       * parameters_type object, which can be used to set the parameters of the
       * factory. Once the parameters have been set, the
       * parameters_type::on() method can be used to obtain an instance
       * of the factory with those parameters.
       *
       * @return a default parameters_type object
       */
      static parameters_type create() { return {}; }
  
  protected:
      /**
       * Automatically propagate loggers from the factory to the product. Use
       * `std::enable_if(...)` to ensure both TheType and TheFactory have logging
       * facilities in this case.
       *
       * @param product  the product to add loggers to
       */
      template <typename TheFactory, typename TheType>
      typename std::enable_if<
          std::is_base_of<log::Loggable, TheType>::value &&
              std::is_base_of<log::Loggable, TheFactory>::value,
          void>::type
      propagate_loggers(TheType *product) const
      {
          for (auto logger : this->loggers_) {
              product->add_logger(logger);
          }
      }
  
      /**
       * Automatically propagate loggers from the factory to the product. Use
       * `std::enable_if(...)` to ensure either TheType or TheFactory do not have
       * logging facilities in this case.
       *
       * @param product  the product to *not* add loggers to
       */
      template <typename TheFactory, typename TheType>
      typename std::enable_if<
          !std::is_base_of<log::Loggable, TheType>::value ||
              !std::is_base_of<log::Loggable, TheFactory>::value,
          void>::type
      propagate_loggers(TheType *product) const
      {}
  
      /**
       * Creates a new factory using the specified executor and parameters.
       *
       * @param exec  the executor where the factory will be constructed
       * @param parameters  the parameters structure for the factory
       */
      explicit EnableDefaultFactory(std::shared_ptr<const Executor> exec,
                                    const parameters_type &parameters = {})
          : EnablePolymorphicObject<ConcreteFactory, PolymorphicBase>(
                std::move(exec)),
            parameters_{parameters}
      {}
  
      std::unique_ptr<abstract_product_type> generate_impl(
          components_type args) const override
      {
          return std::unique_ptr<abstract_product_type>(
              new ProductType(self(), args));
      }
  
  private:
      GKO_ENABLE_SELF(ConcreteFactory);
  
      ParametersType parameters_;
  };
  
  
  /**
   * The enable_parameters_type mixin is used to create a base implementation of
   * the factory parameters structure.
   *
   * It provides only the on() method which can be used to instantiate
   * the factory give the parameters stored in the structure.
   *
   * @tparam ConcreteParametersType  the concrete parameters type which is being
   *                                 implemented [CRTP parameter]
   * @tparam Factory  the concrete factory for which these parameters are being
   *                  used
   */
  template <typename ConcreteParametersType, typename Factory>
  struct enable_parameters_type {
      using factory = Factory;
  
      /**
       * Creates a new factory on the specified executor.
       *
       * @param exec  the executor where the factory will be created
       *
       * @return a new factory instance
       */
      std::unique_ptr<Factory> on(std::shared_ptr<const Executor> exec) const
      {
          return std::unique_ptr<Factory>(new Factory(exec, *self()));
      }
  
  protected:
      GKO_ENABLE_SELF(ConcreteParametersType);
  };
  
  
  }  // namespace gko
  
  
  #endif  // GKO_CORE_BASE_ABSTRACT_FACTORY_HPP_
  