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+/*
+ * Copyright (c) 2017 TOYOTA MOTOR CORPORATION
+ *
+ * Licensed 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.
+ */
+
+#ifndef TMCAGLWM_RESULT_HPP
+#define TMCAGLWM_RESULT_HPP
+
+#include <experimental/optional>
+#include <functional>
+
+namespace wm
+{
+
+using std::experimental::nullopt;
+using std::experimental::optional;
+
+// We only ever return a string as an error - so just parametrize
+// this over result type T
+template <typename T>
+struct result
+{
+ char const *e;
+ optional<T> t;
+
+ bool is_ok() const { return this->t != nullopt; }
+ bool is_err() const { return this->e != nullptr; }
+
+ T unwrap()
+ {
+ if (this->e != nullptr)
+ {
+ throw std::logic_error(this->e);
+ }
+ return this->t.value();
+ }
+
+ operator T() { return this->unwrap(); }
+
+ char const *unwrap_err() { return this->e; }
+
+ optional<T> const &ok() const { return this->t; }
+ optional<char const *> err() const
+ {
+ return this->e ? optional<char const *>(this->e) : nullopt;
+ }
+
+ result<T> map_err(std::function<char const *(char const *)> f);
+};
+
+template <typename T>
+struct result<T> Err(char const *e)
+{
+ return result<T>{e, nullopt};
+}
+
+template <typename T>
+struct result<T> Ok(T t)
+{
+ return result<T>{nullptr, t};
+}
+
+template <typename T>
+result<T> result<T>::map_err(std::function<char const *(char const *)> f)
+{
+ if (this->is_err())
+ {
+ return Err<T>(f(this->e));
+ }
+ return *this;
+}
+
+} // namespace wm
+
+#endif // TMCAGLWM_RESULT_HPP