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   static constexpr PackingStrategy Strategy = PackingStrategy::Variant;
  24
  25   ResultImplementation(ResultImplementation&&) = default;
  26   ResultImplementation(const ResultImplementation&) = delete;
  27   ResultImplementation& operator=(const ResultImplementation&) = delete;
  28   ResultImplementation& operator=(ResultImplementation&&) = default;
  29
  30   explicit ResultImplementation(V&& aValue) : mStorage(std::move(aValue)) {}
  31   explicit ResultImplementation(const V& aValue) : mStorage(aValue) {}
  32   template <typename... Args>
  33   explicit ResultImplementation(std::in_place_t, Args&&... aArgs)
  34       : mStorage(VariantType<V>{}, std::forward<Args>(aArgs)...) {}
  35
  36   explicit ResultImplementation(const E& aErrorValue) : mStorage(aErrorValue) {}
  37   explicit ResultImplementation(E&& aErrorValue)
  38       : mStorage(std::move(aErrorValue)) {}
  39
  40   bool isOk() const { return mStorage.template is<V>(); }
  41
  42   // The callers of these functions will assert isOk() has the proper value, so
  43   // these functions (in all ResultImplementation specializations) don't need
  44   // to do so.
  45   V unwrap() { return std::move(mStorage.template as<V>()); }
  46   const V& inspect() const { return mStorage.template as<V>(); }
  47
  48   E unwrapErr() { return std::move(mStorage.template as<E>()); }
  49   const E& inspectErr() const { return mStorage.template as<E>(); }
  50
  51   void updateAfterTracing(V&& aValue) {
  52     mStorage.template emplace<V>(std::move(aValue));
  53   }
  54   void updateErrorAfterTracing(E&& aErrorValue) {
  55     mStorage.template emplace<E>(std::move(aErrorValue));
  56   }
  57 };
  58
  59 }  // namespace mozilla::detail
  60
  61 #endif  // mozilla_ResultVariant_h