tdlight/td/tl/TlObject.h

//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once

/**
 * \file
 * Contains the declarations of a base class for all TL-objects and some helper methods
 */

#include <cstdint>
#include <memory>
#include <string>
#include <utility>

namespace td {

class TlStorerCalcLength;

class TlStorerUnsafe;

class TlStorerToString;

/**
 * This class is a base class for all TDLib TL-objects.
 */
class TlObject {
 public:
  /**
   * Returns an identifier, uniquely determining the TL-type of the object.
   */
  virtual std::int32_t get_id() const = 0;

  /**
   * Appends the object to the storer serializing object, a buffer of fixed length.
   * \param[in] s Storer to which the object will be appended.
   */
  virtual void store(TlStorerUnsafe &s) const {
  }

  /**
   * Appends the object to the storer, calculating the TL-length of the serialized object.
   * \param[in] s Storer to which the object will be appended.
   */
  virtual void store(TlStorerCalcLength &s) const {
  }

  /**
   * Helper function for the to_string method. Appends a string representation of the object to the storer.
   * \param[in] s Storer to which the object string representation will be appended.
   * \param[in] field_name Object field_name if applicable.
   */
  virtual void store(TlStorerToString &s, const char *field_name) const = 0;

  /**
   * Default constructor.
   */
  TlObject() = default;

  /**
   * Deleted copy constructor.
   */
  TlObject(const TlObject &) = delete;

  /**
   * Deleted copy assignment operator.
   */
  TlObject &operator=(const TlObject &) = delete;

  /**
   * Default move constructor.
   */
  TlObject(TlObject &&) = default;

  /**
   * Default move assignment operator.
   */
  TlObject &operator=(TlObject &&) = default;

  /**
   * Virtual destructor.
   */
  virtual ~TlObject() = default;
};

/**
 * A smart wrapper to store a pointer to a TL-object.
 */
template <class Type>
using tl_object_ptr = std::unique_ptr<Type>;

/**
 * A function to create a dynamically allocated TL-object. Can be treated as an analogue of std::make_unique.
 * Usage example:
 * \code
 * auto get_authorization_state_request = td::make_tl_object<td::td_api::getAuthorizationState>();
 * auto send_message_request = td::make_tl_object<td::td_api::sendMessage>(chat_id, 0, false, false, nullptr,
 *      td::make_tl_object<td::td_api::inputMessageText>("Hello, world!!!", false, true, {}, nullptr));
 * \endcode
 *
 * \tparam Type Type of the TL-object to construct.
 * \param[in] args Arguments to pass to the object constructor.
 * \return Wrapped pointer to the created TL-object.
 */
template <class Type, class... Args>
tl_object_ptr<Type> make_tl_object(Args &&... args) {
  return tl_object_ptr<Type>(new Type(std::forward<Args>(args)...));
}

/**
 * A function to downcast a wrapped pointer to a TL-object to a pointer to its subclass.
 * Casting an object to an incorrect type will lead to undefined behaviour.
 * Examples of usage:
 * \code
 * td::tl_object_ptr<td::td_api::callState> call_state = ...;
 * switch (call_state->get_id()) {
 *   case td::td_api::callStatePending::ID: {
 *     auto state = td::move_tl_object_as<td::td_api::callStatePending>(call_state);
 *     // use state
 *     break;
 *   }
 *   case td::td_api::callStateExchangingKeys::ID: {
 *     // no additional fields, so cast isn't needed
 *     break;
 *   }
 *   case td::td_api::callStateReady::ID: {
 *     auto state = td::move_tl_object_as<td::td_api::callStateReady>(call_state);
 *     // use state
 *     break;
 *   }
 *   case td::td_api::callStateHangingUp::ID: {
 *     // no additional fields, so cast isn't needed
 *     break;
 *   }
 *   case td::td_api::callStateDiscarded::ID: {
 *     auto state = td::move_tl_object_as<td::td_api::callStateDiscarded>(call_state);
 *     // use state
 *     break;
 *   }
 *   case td::td_api::callStateError::ID: {
 *     auto state = td::move_tl_object_as<td::td_api::callStateError>(call_state);
 *     // use state
 *     break;
 *   }
 *   default:
 *     assert(false);
 * }
 * \endcode
 *
 * \tparam ToT Type of a TL-object to move to.
 * \tparam FromT Type of a TL-object to move from, this is auto-deduced.
 * \param[in] from Wrapped pointer to a TL-object.
 */
template <class ToT, class FromT>
tl_object_ptr<ToT> move_tl_object_as(tl_object_ptr<FromT> &from) {
  return tl_object_ptr<ToT>(static_cast<ToT *>(from.release()));
}

/**
 * \overload
 */
template <class ToT, class FromT>
tl_object_ptr<ToT> move_tl_object_as(tl_object_ptr<FromT> &&from) {
  return tl_object_ptr<ToT>(static_cast<ToT *>(from.release()));
}

}  // namespace td