type_adapter.hpp

// Copyright 2021 Open Source Robotics Foundation, Inc.
//
// 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
//
// 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.
 
#ifndef RCLCPP__TYPE_ADAPTER_HPP_
#define RCLCPP__TYPE_ADAPTER_HPP_
 
#include <type_traits>
 
namespace rclcpp
{
 
 
template<typename CustomType, typename ROSMessageType = void, class Enable = void>
struct TypeAdapter
{
  using is_specialized = std::false_type;
  using custom_type = CustomType;
  // In this case, the CustomType is the only thing given, or there is no specialization.
  // Assign ros_message_type to CustomType for the former case.
  using ros_message_type = CustomType;
};
 
template<typename T>
struct is_type_adapter : std::false_type {};
 
template<typename ... Ts>
struct is_type_adapter<TypeAdapter<Ts...>>: std::true_type {};
 
template<typename T>
struct TypeAdapter<T, void, std::enable_if_t<is_type_adapter<T>::value>>: T {};
 
namespace detail
{
 
template<typename CustomType, typename ROSMessageType>
struct assert_type_pair_is_specialized_type_adapter
{
  using type_adapter = TypeAdapter<CustomType, ROSMessageType>;
  static_assert(
    type_adapter::is_specialized::value,
    "No type adapter for this custom type/ros message type pair");
};
 
}  // namespace detail
 
template<typename CustomType>
struct adapt_type
{
  template<typename ROSMessageType>
  using as = typename ::rclcpp::detail::assert_type_pair_is_specialized_type_adapter<
    CustomType,
    ROSMessageType
    >::type_adapter;
};
 
 
template<typename CustomType>
struct ImplicitTypeAdapter
{
  using is_specialized = std::false_type;
};
 
 
template<typename T>
struct TypeAdapter<T, void, std::enable_if_t<ImplicitTypeAdapter<T>::is_specialized::value>>
  : ImplicitTypeAdapter<T>
{};
 
 
#define RCLCPP_USING_CUSTOM_TYPE_AS_ROS_MESSAGE_TYPE(CustomType, ROSMessageType) \
  template<> \
  struct rclcpp::ImplicitTypeAdapter<CustomType> \
    : public rclcpp::TypeAdapter<CustomType, ROSMessageType> \
  { \
    static_assert( \
      is_specialized::value, \
      "Cannot use custom type as ros type when there is no TypeAdapter for that pair"); \
  }
 
}  // namespace rclcpp
 
#endif  // RCLCPP__TYPE_ADAPTER_HPP_