1 files changed, 61 insertions, 0 deletions
diff --git a/mfbt/ResultVariant.h b/mfbt/ResultVariant.h
new file mode 100644
index 0000000000..790ff8d642
--- /dev/null
+++ b/mfbt/ResultVariant.h
@@ -0,0 +1,61 @@
+/* -*- 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