has_save.hpp

/* Copyright © 2017 Apple Inc. All rights reserved.
 *
 * Use of this source code is governed by a BSD-3-clause license that can
 * be found in the LICENSE.txt file or at https://opensource.org/licenses/BSD-3-Clause
 */
#ifndef HAS_SAVE_HPP
#define HAS_SAVE_HPP
#include <typeinfo>
#include <type_traits>
namespace turi {
namespace archive_detail {

  /** SFINAE method to detect if a class T
   * implements a function void T::save(ArcType&) const
   *
   * If T implements the method, has_save_method<ArcType,T>::value will be
   * true. Otherwise it will be false
   */
  template<typename ArcType, typename T>
  struct has_save_method
  {
    template<typename U, void (U::*)(ArcType&) const> struct SFINAE {};
    template<typename U> static char Test(SFINAE<U, &U::save>*);
    template<typename U> static int Test(...);
    static const bool value = sizeof(Test<T>(0)) == sizeof(char);
  };

  /**
   *  save_or_fail<ArcType, T>(arc, t)
   *  will call this version of the function if
   *  T implements void T::save(ArcType&) const.
   *
   * save_or_fail<ArcType, T>(arc, t) will therefore save the class successfully
   * if T implements the save function correctly. Otherwise, calling
   * save_or_fail will print an error message.
   */
  template <typename ArcType, typename ValueType>
  typename std::enable_if<has_save_method<ArcType, ValueType>::value, void>::type
  save_or_fail(ArcType& o, const ValueType &t) {
    t.save(o);
  }

  /**
   *  save_or_fail<ArcType, T>(arc, t)
   *  will call this version of the function if
   *
   * save_or_fail<ArcType, T>(arc, t) will therefore save the class successfully
   * if T implements the save function correctly. Otherwise, calling
   * save_or_fail will print an error message.
   * T does not implement void T::save(ArcType&) const.
   */
  template <typename ArcType, typename ValueType>
  typename std::enable_if<!has_save_method<ArcType, ValueType>::value, void>::type
  save_or_fail(ArcType& o, const ValueType &t) {
    ASSERT_MSG(false,"Trying to serializable type %s without valid save method.", typeid(ValueType).name());
  }

}  // archive_detail
}  // turicreate

#endif