gecko-dev/mfbt/ResultVariant.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* A type suitable for returning either a value or an error from a function. */

#ifndef mozilla_ResultVariant_h
#define mozilla_ResultVariant_h

#include "mozilla/MaybeStorageBase.h"
#include "mozilla/Result.h"
#include "mozilla/Variant.h"

namespace mozilla::detail {

template <typename V, typename E>
class ResultImplementation<V, E, PackingStrategy::Variant> {
  mozilla::Variant<V, E> mStorage;

 public:
  static constexpr PackingStrategy Strategy = PackingStrategy::Variant;

  ResultImplementation(ResultImplementation&&) = default;
  ResultImplementation(const ResultImplementation&) = delete;
  ResultImplementation& operator=(const ResultImplementation&) = delete;
  ResultImplementation& operator=(ResultImplementation&&) = default;

  explicit ResultImplementation(V&& aValue) : mStorage(std::move(aValue)) {}
  explicit ResultImplementation(const V& aValue) : mStorage(aValue) {}
  template <typename... Args>
  explicit ResultImplementation(std::in_place_t, Args&&... aArgs)
      : mStorage(VariantType<V>{}, std::forward<Args>(aArgs)...) {}

  explicit ResultImplementation(const E& aErrorValue) : mStorage(aErrorValue) {}
  explicit ResultImplementation(E&& aErrorValue)
      : mStorage(std::move(aErrorValue)) {}

  bool isOk() const { return mStorage.template is<V>(); }

  // The callers of these functions will assert isOk() has the proper value, so
  // these functions (in all ResultImplementation specializations) don't need
  // to do so.
  V unwrap() { return std::move(mStorage.template as<V>()); }
  const V& inspect() const { return mStorage.template as<V>(); }

  E unwrapErr() { return std::move(mStorage.template as<E>()); }
  const E& inspectErr() const { return mStorage.template as<E>(); }

  void updateAfterTracing(V&& aValue) {
    mStorage.template emplace<V>(std::move(aValue));
  }
  void updateErrorAfterTracing(E&& aErrorValue) {
    mStorage.template emplace<E>(std::move(aErrorValue));
  }
};

}  // namespace mozilla::detail

#endif  // mozilla_ResultVariant_h