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tdutils/td/utils/optional.h

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#pragma once
+
+#include "td/utils/common.h"
+#include "td/utils/Status.h"
+
+#include <type_traits>
+#include <utility>
+
+namespace td {
+
+template <class T, bool = std::is_copy_constructible<T>::value>
+class optional {
+ public:
+  optional() = default;
+  template <class T1,
+            std::enable_if_t<!std::is_same<std::decay_t<T1>, optional>::value && std::is_constructible<T, T1>::value,
+                             int> = 0>
+  optional(T1 &&t) : impl_(std::forward<T1>(t)) {
+  }
+
+  optional(const optional &other) {
+    if (other) {
+      impl_ = Result<T>(other.value());
+    }
+  }
+
+  optional &operator=(const optional &other) {
+    if (other) {
+      impl_ = Result<T>(other.value());
+    } else {
+      impl_ = Result<T>();
+    }
+    return *this;
+  }
+
+  optional(optional &&other) = default;
+  optional &operator=(optional &&other) = default;
+  ~optional() = default;
+
+  explicit operator bool() const {
+    return impl_.is_ok();
+  }
+  T &value() {
+    return impl_.ok_ref();
+  }
+  const T &value() const {
+    return impl_.ok_ref();
+  }
+  T &operator*() {
+    return value();
+  }
+  T unwrap() {
+    CHECK(*this);
+    auto res = std::move(value());
+    impl_ = {};
+    return res;
+  }
+
+  template <class... ArgsT>
+  void emplace(ArgsT &&... args) {
+    impl_.emplace(std::forward<ArgsT>(args)...);
+  }
+
+ private:
+  Result<T> impl_;
+};
+
+template <typename T>
+struct optional<T, false> : optional<T, true> {
+  optional() = default;
+
+  using optional<T, true>::optional;
+
+  optional(const optional &other) = delete;
+  optional &operator=(const optional &other) = delete;
+  optional(optional &&) = default;
+  optional &operator=(optional &&) = default;
+  ~optional() = default;
+};
+
+}  // namespace td