/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#include <vector>

namespace folly {

template <class Value>
class Optional;

struct None {
  enum class _secret { _token };
  explicit constexpr None(_secret) {}
};
constexpr None none{None::_secret::_token};

template <class Value>
class Optional {
 public:
  typedef Value value_type;

  constexpr Optional();

  Optional(const Optional& src);

  constexpr Optional(const None&) noexcept;

  constexpr Optional(const Value& newValue);

  void assign(const None&);

  void assign(const Optional& src);

  Optional& operator=(None) noexcept {
    reset();
    return *this;
  }

  Optional& operator=(const Optional& other) {
    assign(other);
    return *this;
  }

  template <class... Args>
  Value& emplace(Args&&... args);

  void reset() noexcept;

  constexpr Value& value() &;

  constexpr bool has_value() const noexcept;

  constexpr explicit operator bool() const noexcept { return has_value(); }

  constexpr const Value* operator->() const { return &value(); }

  constexpr Value* operator->() { return &value(); }

  template <class U>
  constexpr Value value_or(U&& dflt) const&;
};
} // namespace folly

int not_none_ok() {
  folly::Optional<int> foo{5};
  return foo.value();
}

int none_check_ok() {
  folly::Optional<int> foo{folly::none};
  if (foo) {
    return foo.value();
  }
  return -1;
}

int none_no_check_bad() {
  folly::Optional<int> foo{folly::none};
  return foo.value();
}

int none_copy_ok() {
  folly::Optional<int> foo{5};
  folly::Optional<int> bar{foo};
  return bar.value();
}

int none_copy_bad() {
  folly::Optional<int> foo{folly::none};
  folly::Optional<int> bar{foo};
  return bar.value();
}

int assign_ok() {
  folly::Optional<int> foo{5};
  folly::Optional<int> bar{foo};
  foo = folly::none;
  return bar.value();
}

int assign_bad() {
  folly::Optional<int> foo{folly::none};
  folly::Optional<int> bar{5};
  int sum = bar.value();
  bar = foo;
  sum += bar.value();
  return sum;
}

int assign2_bad() {
  folly::Optional<int> foo{5};
  int sum = foo.value();
  foo = folly::none;
  sum += foo.value();
  return sum;
}

struct State {
  std::vector<int> vec;
};

void emplace(folly::Optional<State> state) {
  if (state) {
    state.emplace();
  }
  auto pos = state->vec.begin();
}

void operator_arrow_bad() { emplace(folly::none); }

int value_or_check_empty_ok() {
  folly::Optional<int> foo{folly::none};
  if (foo.value_or(0) > 0) {
    return foo.value();
  }
  return -1;
}