mfbt/ResultVariant.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* A type suitable for returning either a value or an error from a function. */
   8
   9 #ifndef mozilla_ResultVariant_h
  10 #define mozilla_ResultVariant_h
  11
  12 #include "mozilla/MaybeStorageBase.h"
  13 #include "mozilla/Result.h"
  14 #include "mozilla/Variant.h"
  15
  16 namespace mozilla::detail {
  17
  18 template <typename V, typename E>
  19 class ResultImplementation<V, E, PackingStrategy::Variant> {
  20   mozilla::Variant<V, E> mStorage;
  21
  22  public:
  23   ResultImplementation(ResultImplementation&&) = default;
  24   ResultImplementation(const ResultImplementation&) = delete;
  25   ResultImplementation& operator=(const ResultImplementation&) = delete;
  26   ResultImplementation& operator=(ResultImplementation&&) = default;
  27
  28   explicit ResultImplementation(V&& aValue)
  29       : mStorage(std::forward<V>(aValue)) {}
  30   explicit ResultImplementation(const V& aValue) : mStorage(aValue) {}
  31   template <typename... Args>
  32   explicit ResultImplementation(std::in_place_t, Args&&... aArgs)
  33       : mStorage(VariantType<V>{}, std::forward<Args>(aArgs)...) {}
  34
  35   explicit ResultImplementation(const E& aErrorValue) : mStorage(aErrorValue) {}
  36   explicit ResultImplementation(E&& aErrorValue)
  37       : mStorage(std::forward<E>(aErrorValue)) {}
  38
  39   bool isOk() const { return mStorage.template is<V>(); }
  40
  41   // The callers of these functions will assert isOk() has the proper value, so
  42   // these functions (in all ResultImplementation specializations) don't need
  43   // to do so.
  44   V unwrap() { return std::move(mStorage.template as<V>()); }
  45   const V& inspect() const { return mStorage.template as<V>(); }
  46
  47   E unwrapErr() { return std::move(mStorage.template as<E>()); }
  48   const E& inspectErr() const { return mStorage.template as<E>(); }
  49 };
  50
  51 }  // namespace mozilla::detail
  52
  53 #endif  // mozilla_ResultVariant_h