cpp/src/graphar/result.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

#pragma once

#include <utility>

#include "graphar/fwd.h"
#include "graphar/status.h"

#define GAR_ASSIGN_OR_RAISE_IMPL(result_name, lhs, rexpr)          \
  auto&& result_name = (rexpr);                                    \
  GAR_RETURN_IF_((result_name).has_error(), (result_name).error(), \
                 GAR_STRINGIFY(rexpr));                            \
  lhs = std::move(result_name).value();

#define GAR_ASSIGN_OR_RAISE_ERROR_IMPL(result_name, lhs, rexpr)         \
  auto&& result_name = (rexpr);                                         \
  GAR_RAISE_ERROR_IF_((result_name).has_error(), (result_name).error(), \
                      GAR_STRINGIFY(rexpr));                            \
  lhs = std::move(result_name).value();

#define GAR_ASSIGN_OR_RAISE_NAME(x, y) GAR_CONCAT(x, y)

/**
 * @brief Execute an expression that returns a Result, extracting its value
 * into the variable defined by `lhs` (or returning a Status on error).
 *
 * Example: Assigning to a new value:
 *   GAR_ASSIGN_OR_RAISE(auto value, MaybeGetValue(arg));
 *
 * Example: Assigning to an existing value:
 *   ValueType value;
 *   GAR_ASSIGN_OR_RAISE(value, MaybeGetValue(arg));
 *
 * WARNING: GAR_ASSIGN_OR_RAISE expands into multiple statements;
 * it cannot be used in a single statement (e.g. as the body of an if
 * statement without {})!
 *
 * WARNING: GAR_ASSIGN_OR_RAISE `std::move`s its right operand. If you have
 * an lvalue Result which you *don't* want to move out of cast appropriately.
 *
 * WARNING: GAR_ASSIGN_OR_RAISE is not a single expression; it will not
 * maintain lifetimes of all temporaries in `rexpr` (e.g.
 * `GAR_ASSIGN_OR_RAISE(auto x, MakeTemp().GetResultRef());`
 * will most likely segfault)!
 */
#define GAR_ASSIGN_OR_RAISE(lhs, rexpr) \
  GAR_ASSIGN_OR_RAISE_IMPL(             \
      GAR_ASSIGN_OR_RAISE_NAME(_error_or_value, __COUNTER__), lhs, rexpr);

/**
 * @brief Execute an expression that returns a Result, extracting its value
 * into the variable defined by `lhs` (or throw an runtime error).
 *
 * Example: Assigning to a new value:
 *   GAR_ASSIGN_OR_RAISE_ERROR(auto value, MaybeGetValue(arg));
 *
 * Example: Assigning to an existing value:
 *   ValueType value;
 *   GAR_ASSIGN_OR_RAISE_ERROR(value, MaybeGetValue(arg));
 */
#define GAR_ASSIGN_OR_RAISE_ERROR(lhs, rexpr) \
  GAR_ASSIGN_OR_RAISE_ERROR_IMPL(             \
      GAR_ASSIGN_OR_RAISE_NAME(_error_or_value, __COUNTER__), lhs, rexpr);

#define GAR_RETURN_ON_ARROW_ERROR_AND_ASSIGN_IMPL(result_name, lhs, rexpr) \
  auto&& result_name = (rexpr);                                            \
  if (!result_name.status().ok()) {                                        \
    return ::graphar::Status::ArrowError(result_name.status().ToString()); \
  }                                                                        \
  lhs = std::move(result_name).ValueOrDie();

/**
 * @brief Execute an expression that returns a Arrow Result, extracting its
 * value into the variable defined by `lhs` (or returning a Status on error).
 *
 * Example: Assigning to a new value:
 *   GAR_ASSIGN_OR_RAISE(auto value, MaybeGetValue(arg));
 *
 * Example: Assigning to an existing value:
 *   ValueType value;
 *   GAR_ASSIGN_OR_RAISE(value, MaybeGetValue(arg));
 */
#define GAR_RETURN_ON_ARROW_ERROR_AND_ASSIGN(lhs, rexpr) \
  GAR_RETURN_ON_ARROW_ERROR_AND_ASSIGN_IMPL(             \
      GAR_ASSIGN_OR_RAISE_NAME(_error_or_value, __COUNTER__), lhs, rexpr);

namespace graphar::internal {

// Extract Status from Status or Result<T>
// Useful for the status check macros such as RETURN_NOT_OK.
template <typename T>
inline const Status& GenericToStatus(const Result<T>& res) {
  return res.status();
}
template <typename T>
inline Status GenericToStatus(Result<T>&& res) {
  return std::move(res).status();
}

}  // namespace graphar::internal