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///
// optional - An implementation of std::optional with extensions
// Written in 2017 by Simon Brand (tartanllama@gmail.com, @TartanLlama)
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to the
// public domain worldwide. This software is distributed without any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software. If not, see
// <http://creativecommons.org/publicdomain/zero/1.0/>.
///

#ifndef TL_OPTIONAL_HPP
#define TL_OPTIONAL_HPP

#define TL_OPTIONAL_VERSION_MAJOR 0
#define TL_OPTIONAL_VERSION_MINOR 5

#include <functional>
#include <new>
#include <optional>
#include <type_traits>
#include <utility>
#include <map>
#include <iostream>
#include <string>

#if (defined(_MSC_VER) && _MSC_VER == 1900)
#define TL_OPTIONAL_MSVC2015
#endif

#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 && \
 !defined(__clang__))
#define TL_OPTIONAL_GCC49
#endif

#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 4 && \
 !defined(__clang__))
#define TL_OPTIONAL_GCC54
#endif

#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 5 && \
 !defined(__clang__))
#define TL_OPTIONAL_GCC55
#endif

#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 && \
 !defined(__clang__))
// GCC < 5 doesn't support overloading on const&& for member functions
#define TL_OPTIONAL_NO_CONSTRR

// GCC < 5 doesn't support some standard C++11 type traits
#define TL_OPTIONAL_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) \
 std::has_trivial_copy_constructor<T>::value
#define TL_OPTIONAL_IS_TRIVIALLY_COPY_ASSIGNABLE(T) \
 std::has_trivial_copy_assign<T>::value

// This one will be different for GCC 5.7 if it's ever supported
#define TL_OPTIONAL_IS_TRIVIALLY_DESTRUCTIBLE(T) \
 std::is_trivially_destructible<T>::value

// GCC 5 < v < 8 has a bug in is_trivially_copy_constructible which breaks
// std::vector for non-copyable types
#elif (defined(__GNUC__) && __GNUC__ < 8 && !defined(__clang__))
#ifndef TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
#define TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
namespace tl {
namespace detail {
template <class T>
struct is_trivially_copy_constructible
 : std::is_trivially_copy_constructible<T> {};
#ifdef _GLIBCXX_VECTOR
template <class T, class A>
struct is_trivially_copy_constructible<std::vector<T, A>>
 : std::is_trivially_copy_constructible<T> {};
#endif
} // namespace detail
} // namespace tl
#endif

#define TL_OPTIONAL_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) \
 tl::detail::is_trivially_copy_constructible<T>::value
#define TL_OPTIONAL_IS_TRIVIALLY_COPY_ASSIGNABLE(T) \
 std::is_trivially_copy_assignable<T>::value
#define TL_OPTIONAL_IS_TRIVIALLY_DESTRUCTIBLE(T) \
 std::is_trivially_destructible<T>::value
#else
#define TL_OPTIONAL_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) \
 std::is_trivially_copy_constructible<T>::value
#define TL_OPTIONAL_IS_TRIVIALLY_COPY_ASSIGNABLE(T) \
 std::is_trivially_copy_assignable<T>::value
#define TL_OPTIONAL_IS_TRIVIALLY_DESTRUCTIBLE(T) \
 std::is_trivially_destructible<T>::value
#endif

#if __cplusplus > 201103L
#define TL_OPTIONAL_CXX14
#endif

// constexpr implies const in C++11, not C++14
#if (__cplusplus == 201103L || defined(TL_OPTIONAL_MSVC2015) ||                \
     defined(TL_OPTIONAL_GCC49))
#define TL_OPTIONAL_11_CONSTEXPR
#else
#define TL_OPTIONAL_11_CONSTEXPR constexpr
#endif

namespace tl {
#ifndef TL_MONOSTATE_INPLACE_MUTEX
#define TL_MONOSTATE_INPLACE_MUTEX
/// Used to represent an optional with no data; essentially a bool
class monostate {};

///  A tag type to tell optional to construct its value in-place
struct in_place_t {
  explicit in_place_t() = default;
};
/// A tag to tell optional to construct its value in-place
static constexpr in_place_t in_place{};
#endif

template <class T> class optional;

namespace detail {
#ifndef TL_TRAITS_MUTEX
#define TL_TRAITS_MUTEX
// C++14-style aliases for brevity
template <class T> using remove_const_t = typename std::remove_const<T>::type;
template <class T>
using remove_reference_t = typename std::remove_reference<T>::type;
template <class T> using decay_t = typename std::decay<T>::type;
template <bool E, class T = void>
using enable_if_t = typename std::enable_if<E, T>::type;
template <bool B, class T, class F>
using conditional_t = typename std::conditional<B, T, F>::type;

// std::conjunction from C++17
template <class...> struct conjunction : std::true_type {};
template <class B> struct conjunction : B {};
template <class B, class... Bs>
struct conjunction<B, Bs...>
 : std::conditional<bool(B::value), conjunction<Bs...>, B>::type {};

#if defined(_LIBCPP_VERSION) && __cplusplus == 201103L
#define TL_OPTIONAL_LIBCXX_MEM_FN_WORKAROUND
#endif

// In C++11 mode, there's an issue in libc++'s std::mem_fn
// which results in a hard-error when using it in a noexcept expression
// in some cases. This is a check to workaround the common failing case.
#ifdef TL_OPTIONAL_LIBCXX_MEM_FN_WORKAROUND
template <class T>
struct is_pointer_to_non_const_member_func : std::false_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...)>
 : std::true_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) &>
 : std::true_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) &&>
 : std::true_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile>
 : std::true_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile &>
 : std::true_type {};
template <class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile &&>
 : std::true_type {};

template <class T> struct is_const_or_const_ref : std::false_type {};
template <class T> struct is_const_or_const_ref<T const &> : std::true_type {};
template <class T> struct is_const_or_const_ref<T const> : std::true_type {};
#endif

// std::invoke from C++17
// https://stackoverflow.com/questions/38288042/c11-14-invoke-workaround
template <
 typename Fn, typename... Args,
#ifdef TL_OPTIONAL_LIBCXX_MEM_FN_WORKAROUND
 typename = enable_if_t<!(is_pointer_to_non_const_member_func<Fn>::value &&
 is_const_or_const_ref<Args...>::value)>,
#endif
 typename = enable_if_t<std::is_member_pointer<decay_t<Fn>>::value>, int = 0>
constexpr auto invoke(Fn &&f, Args &&...args) noexcept(
 noexcept(std::mem_fn(f)(std::forward<Args>(args)...)))
 -> decltype(std::mem_fn(f)(std::forward<Args>(args)...)) {
 return std::mem_fn(f)(std::forward<Args>(args)...);
}

template <typename Fn, typename... Args,
 typename = enable_if_t<!std::is_member_pointer<decay_t<Fn>>::value>>
constexpr auto invoke(Fn &&f, Args &&...args) noexcept(
 noexcept(std::forward<Fn>(f)(std::forward<Args>(args)...)))
 -> decltype(std::forward<Fn>(f)(std::forward<Args>(args)...)) {
 return std::forward<Fn>(f)(std::forward<Args>(args)...);
}

// std::invoke_result from C++17
template <class F, class, class... Us> struct invoke_result_impl;

template <class F, class... Us>
struct invoke_result_impl<
 F,
 decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...), void()),
 Us...> {
 using type =
 decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...));
};

template <class F, class... Us>
using invoke_result = invoke_result_impl<F, void, Us...>;

template <class F, class... Us>
using invoke_result_t = typename invoke_result<F, Us...>::type;

#if defined(_MSC_VER) && _MSC_VER <= 1900
// TODO make a version which works with MSVC 2015
template <class T, class U = T> struct is_swappable : std::true_type {};

template <class T, class U = T> struct is_nothrow_swappable : std::true_type {};
#else
// https://stackoverflow.com/questions/26744589/what-is-a-proper-way-to-implement-is-swappable-to-test-for-the-swappable-concept
namespace swap_adl_tests {
// if swap ADL finds this then it would call std::swap otherwise (same
// signature)
struct tag {};

template <class T> tag swap(T &, T &);
template <class T, std::size_t N> tag swap(T (&a)[N], T (&b)[N]);

// helper functions to test if an unqualified swap is possible, and if it
// becomes std::swap
template <class, class> std::false_type can_swap(...) noexcept(false);
template <class T, class U,
 class = decltype(swap(std::declval<T &>(), std::declval()))>
std::true_type can_swap(int) noexcept(noexcept(swap(std::declval<T &>(),
 std::declval())));

template <class, class> std::false_type uses_std(...);
template <class T, class U>
std::is_same<decltype(swap(std::declval<T &>(), std::declval())), tag>
uses_std(int);

template <class T>
struct is_std_swap_noexcept
 : std::integral_constant<bool,
 std::is_nothrow_move_constructible<T>::value &&
 std::is_nothrow_move_assignable<T>::value> {};

template <class T, std::size_t N>
struct is_std_swap_noexcept<T[N]> : is_std_swap_noexcept<T> {};

template <class T, class U>
struct is_adl_swap_noexcept
 : std::integral_constant<bool, noexcept(can_swap<T, U>(0))> {};
} // namespace swap_adl_tests

template <class T, class U = T>
struct is_swappable
 : std::integral_constant<
 bool,
 decltype(detail::swap_adl_tests::can_swap<T, U>(0))::value &&
 (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value ||
 (std::is_move_assignable<T>::value &&
 std::is_move_constructible<T>::value))> {};

template <class T, std::size_t N>
struct is_swappable<T[N], T[N]>
 : std::integral_constant<
 bool,
 decltype(detail::swap_adl_tests::can_swap<T[N], T[N]>(0))::value &&
 (!decltype(
 detail::swap_adl_tests::uses_std<T[N], T[N]>(0))::value ||
 is_swappable<T, T>::value)> {};

template <class T, class U = T>
struct is_nothrow_swappable
 : std::integral_constant<
 bool,
 is_swappable<T, U>::value &&
 ((decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value
 &&detail::swap_adl_tests::is_std_swap_noexcept<T>::value) ||
 (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value &&
 detail::swap_adl_tests::is_adl_swap_noexcept<T,
 U>::value))> {
};
#endif
#endif

// std::void_t from C++17
template <class...> struct voider { using type = void; };
template <class... Ts> using void_t = typename voider<Ts...>::type;

// Trait for checking if a type is a tl::optional
template <class T> struct is_optional_impl : std::false_type {};
template <class T> struct is_optional_impl<optional<T>> : std::true_type {};
template <class T> using is_optional = is_optional_impl<decay_t<T>>;

// Change void to tl::monostate
template <class U>
using fixup_void = conditional_t<std::is_void::value, monostate, U>;

template <class F, class U, class = invoke_result_t<F, U>>
using get_map_return = optional<fixup_void<invoke_result_t<F, U>>>;

// Check if invoking F for some Us returns void
template <class F, class = void, class... U> struct returns_void_impl;
template <class F, class... U>
struct returns_void_impl<F, void_t<invoke_result_t<F, U...>>, U...>
 : std::is_void<invoke_result_t<F, U...>> {};
template <class F, class... U>
using returns_void = returns_void_impl<F, void, U...>;

template <class T, class... U>
using enable_if_ret_void = enable_if_t<returns_void<T &&, U...>::value>;

template <class T, class... U>
using disable_if_ret_void = enable_if_t<!returns_void<T &&, U...>::value>;

template <class T, class U>
using enable_forward_value =
 detail::enable_if_t<std::is_constructible<T, U &&>::value &&
 !std::is_same<detail::decay_t, in_place_t>::value &&
 !std::is_same<optional<T>, detail::decay_t>::value>;

template <class T, class U, class Other>
using enable_from_other = detail::enable_if_t<
 std::is_constructible<T, Other>::value &&
 !std::is_constructible<T, optional &>::value &&
 !std::is_constructible<T, optional &&>::value &&
 !std::is_constructible<T, const optional &>::value &&
 !std::is_constructible<T, const optional &&>::value &&
 !std::is_convertible<optional &, T>::value &&
 !std::is_convertible<optional &&, T>::value &&
 !std::is_convertible<const optional &, T>::value &&
 !std::is_convertible<const optional &&, T>::value>;

template <class T, class U>
using enable_assign_forward = detail::enable_if_t<
 !std::is_same<optional<T>, detail::decay_t>::value &&
 !detail::conjunction<std::is_scalar<T>,
 std::is_same<T, detail::decay_t>>::value &&
 std::is_constructible<T, U>::value && std::is_assignable<T &, U>::value>;

template <class T, class U, class Other>
using enable_assign_from_other = detail::enable_if_t<
 std::is_constructible<T, Other>::value &&
 std::is_assignable<T &, Other>::value &&
 !std::is_constructible<T, optional &>::value &&
 !std::is_constructible<T, optional &&>::value &&
 !std::is_constructible<T, const optional &>::value &&
 !std::is_constructible<T, const optional &&>::value &&
 !std::is_convertible<optional &, T>::value &&
 !std::is_convertible<optional &&, T>::value &&
 !std::is_convertible<const optional &, T>::value &&
 !std::is_convertible<const optional &&, T>::value &&
 !std::is_assignable<T &, optional &>::value &&
 !std::is_assignable<T &, optional &&>::value &&
 !std::is_assignable<T &, const optional &>::value &&
 !std::is_assignable<T &, const optional &&>::value>;

// The storage base manages the actual storage, and correctly propagates
// trivial destruction from T. This case is for when T is not trivially
// destructible.
template <class T, bool = ::std::is_trivially_destructible<T>::value>
struct optional_storage_base {
 TL_OPTIONAL_11_CONSTEXPR optional_storage_base() noexcept : m_dummy() {}

template <class... U>
 TL_OPTIONAL_11_CONSTEXPR optional_storage_base(in_place_t, U &&...u)
 : m_value(std::forward(u)...), m_hasValue(true) {}

~optional_storage_base() {
    if (m_hasValue) {
      m_value.~T();
      m_hasValue = false;
    }
  }

struct dummy {};
  union {
    dummy m_dummy;
    T m_value;
  };

bool m_hasValue = false;
};

// This case is for when T is trivially destructible.
template <class T> struct optional_storage_base<T, true> {
 TL_OPTIONAL_11_CONSTEXPR optional_storage_base() noexcept : m_dummy() {}

template <class... U>
 TL_OPTIONAL_11_CONSTEXPR optional_storage_base(in_place_t, U &&...u)
 : m_value(std::forward(u)...), m_hasValue(true) {}

// No destructor, so this class is trivially destructible

struct dummy {};
  union {
    dummy m_dummy;
    T m_value;
  };

bool m_hasValue = false;
};

// This base class provides some handy member functions which can be used in
// further derived classes
template <class T> struct optional_operations_base : optional_storage_base<T> {
 using optional_storage_base<T>::optional_storage_base;

void hard_reset() noexcept {
    get().~T();
    this->m_hasValue = false;
  }

template <class... Args> void construct(Args &&...args) noexcept {
 new (std::addressof(this->m_value)) T(std::forward<Args>(args)...);
 this->m_hasValue = true;
 }

template <class Opt> void assign(Opt &&rhs) {
 if (this->hasValue()) {
 if (rhs.hasValue()) {
 this->m_value = std::forward<Opt>(rhs).get();
 } else {
 this->m_value.~T();
 this->m_hasValue = false;
 }
 }

else if (rhs.hasValue()) {
 construct(std::forward<Opt>(rhs).get());
 }
 }

bool hasValue() const { return this->m_hasValue; }

TL_OPTIONAL_11_CONSTEXPR T &get() & { return this->m_value; }
  TL_OPTIONAL_11_CONSTEXPR const T &get() const & { return this->m_value; }
  TL_OPTIONAL_11_CONSTEXPR T &&get() && { return std::move(this->m_value); }
#ifndef TL_OPTIONAL_NO_CONSTRR
  constexpr const T &&get() const && { return std::move(this->m_value); }
#endif
};

// This class manages conditionally having a trivial copy constructor
// This specialization is for when T is trivially copy constructible
template <class T, bool = TL_OPTIONAL_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)>
struct optional_copy_base : optional_operations_base<T> {
 using optional_operations_base<T>::optional_operations_base;
};

// This specialization is for when T is not trivially copy constructible
template <class T>
struct optional_copy_base<T, false> : optional_operations_base<T> {
 using optional_operations_base<T>::optional_operations_base;

optional_copy_base() = default;
  optional_copy_base(const optional_copy_base &rhs) {
    if (rhs.hasValue()) {
      this->construct(rhs.get());
    } else {
      this->m_hasValue = false;
    }
  }

optional_copy_base(optional_copy_base &&rhs) = default;
  optional_copy_base &operator=(const optional_copy_base &rhs) = default;
  optional_copy_base &operator=(optional_copy_base &&rhs) = default;
};

// This class manages conditionally having a trivial move constructor
// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
// doesn't implement an analogue to std::is_trivially_move_constructible. We
// have to make do with a non-trivial move constructor even if T is trivially
// move constructible
#ifndef TL_OPTIONAL_GCC49
template <class T, bool = std::is_trivially_move_constructible<T>::value>
struct optional_move_base : optional_copy_base<T> {
 using optional_copy_base<T>::optional_copy_base;
};
#else
template <class T, bool = false> struct optional_move_base;
#endif
template <class T> struct optional_move_base<T, false> : optional_copy_base<T> {
 using optional_copy_base<T>::optional_copy_base;

optional_move_base() = default;
  optional_move_base(const optional_move_base &rhs) = default;

optional_move_base(optional_move_base &&rhs) noexcept(
 std::is_nothrow_move_constructible<T>::value) {
 if (rhs.hasValue()) {
 this->construct(std::move(rhs.get()));
 } else {
 this->m_hasValue = false;
 }
 }
 optional_move_base &operator=(const optional_move_base &rhs) = default;
 optional_move_base &operator=(optional_move_base &&rhs) = default;
};

// This class manages conditionally having a trivial copy assignment operator
template <class T, bool = TL_OPTIONAL_IS_TRIVIALLY_COPY_ASSIGNABLE(T) &&
 TL_OPTIONAL_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) &&
 TL_OPTIONAL_IS_TRIVIALLY_DESTRUCTIBLE(T)>
struct optional_copy_assign_base : optional_move_base<T> {
 using optional_move_base<T>::optional_move_base;
};

template <class T>
struct optional_copy_assign_base<T, false> : optional_move_base<T> {
 using optional_move_base<T>::optional_move_base;

optional_copy_assign_base() = default;
  optional_copy_assign_base(const optional_copy_assign_base &rhs) = default;

optional_copy_assign_base(optional_copy_assign_base &&rhs) = default;
  optional_copy_assign_base &operator=(const optional_copy_assign_base &rhs) {
    this->assign(rhs);
    return *this;
  }
  optional_copy_assign_base &
  operator=(optional_copy_assign_base &&rhs) = default;
};

// This class manages conditionally having a trivial move assignment operator
// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
// doesn't implement an analogue to std::is_trivially_move_assignable. We have
// to make do with a non-trivial move assignment operator even if T is trivially
// move assignable
#ifndef TL_OPTIONAL_GCC49
template <class T, bool = std::is_trivially_destructible<T>::value
 &&std::is_trivially_move_constructible<T>::value
 &&std::is_trivially_move_assignable<T>::value>
struct optional_move_assign_base : optional_copy_assign_base<T> {
 using optional_copy_assign_base<T>::optional_copy_assign_base;
};
#else
template <class T, bool = false> struct optional_move_assign_base;
#endif

template <class T>
struct optional_move_assign_base<T, false> : optional_copy_assign_base<T> {
 using optional_copy_assign_base<T>::optional_copy_assign_base;

optional_move_assign_base() = default;
  optional_move_assign_base(const optional_move_assign_base &rhs) = default;

optional_move_assign_base(optional_move_assign_base &&rhs) = default;

optional_move_assign_base &
  operator=(const optional_move_assign_base &rhs) = default;

optional_move_assign_base &
 operator=(optional_move_assign_base &&rhs) noexcept(
 std::is_nothrow_move_constructible<T>::value
 &&std::is_nothrow_move_assignable<T>::value) {
 this->assign(std::move(rhs));
 return *this;
 }
};

// optional_delete_ctor_base will conditionally delete copy and move
// constructors depending on whether T is copy/move constructible
template <class T, bool EnableCopy = std::is_copy_constructible<T>::value,
 bool EnableMove = std::is_move_constructible<T>::value>
struct optional_delete_ctor_base {
 optional_delete_ctor_base() = default;
 optional_delete_ctor_base(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base(optional_delete_ctor_base &&) noexcept = default;
 optional_delete_ctor_base &
 operator=(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base &
 operator=(optional_delete_ctor_base &&) noexcept = default;
};

template <class T> struct optional_delete_ctor_base<T, true, false> {
 optional_delete_ctor_base() = default;
 optional_delete_ctor_base(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base(optional_delete_ctor_base &&) noexcept = delete;
 optional_delete_ctor_base &
 operator=(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base &
 operator=(optional_delete_ctor_base &&) noexcept = default;
};

template <class T> struct optional_delete_ctor_base<T, false, true> {
 optional_delete_ctor_base() = default;
 optional_delete_ctor_base(const optional_delete_ctor_base &) = delete;
 optional_delete_ctor_base(optional_delete_ctor_base &&) noexcept = default;
 optional_delete_ctor_base &
 operator=(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base &
 operator=(optional_delete_ctor_base &&) noexcept = default;
};

template <class T> struct optional_delete_ctor_base<T, false, false> {
 optional_delete_ctor_base() = default;
 optional_delete_ctor_base(const optional_delete_ctor_base &) = delete;
 optional_delete_ctor_base(optional_delete_ctor_base &&) noexcept = delete;
 optional_delete_ctor_base &
 operator=(const optional_delete_ctor_base &) = default;
 optional_delete_ctor_base &
 operator=(optional_delete_ctor_base &&) noexcept = default;
};

// optional_delete_assign_base will conditionally delete copy and move
// constructors depending on whether T is copy/move constructible + assignable
template <class T,
 bool EnableCopy = (std::is_copy_constructible<T>::value &&
 std::is_copy_assignable<T>::value),
 bool EnableMove = (std::is_move_constructible<T>::value &&
 std::is_move_assignable<T>::value)>
struct optional_delete_assign_base {
 optional_delete_assign_base() = default;
 optional_delete_assign_base(const optional_delete_assign_base &) = default;
 optional_delete_assign_base(optional_delete_assign_base &&) noexcept =
 default;
 optional_delete_assign_base &
 operator=(const optional_delete_assign_base &) = default;
 optional_delete_assign_base &
 operator=(optional_delete_assign_base &&) noexcept = default;
};

template <class T> struct optional_delete_assign_base<T, true, false> {
 optional_delete_assign_base() = default;
 optional_delete_assign_base(const optional_delete_assign_base &) = default;
 optional_delete_assign_base(optional_delete_assign_base &&) noexcept =
 default;
 optional_delete_assign_base &
 operator=(const optional_delete_assign_base &) = default;
 optional_delete_assign_base &
 operator=(optional_delete_assign_base &&) noexcept = delete;
};

template <class T> struct optional_delete_assign_base<T, false, true> {
 optional_delete_assign_base() = default;
 optional_delete_assign_base(const optional_delete_assign_base &) = default;
 optional_delete_assign_base(optional_delete_assign_base &&) noexcept =
 default;
 optional_delete_assign_base &
 operator=(const optional_delete_assign_base &) = delete;
 optional_delete_assign_base &
 operator=(optional_delete_assign_base &&) noexcept = default;
};

template <class T> struct optional_delete_assign_base<T, false, false> {
 optional_delete_assign_base() = default;
 optional_delete_assign_base(const optional_delete_assign_base &) = default;
 optional_delete_assign_base(optional_delete_assign_base &&) noexcept =
 default;
 optional_delete_assign_base &
 operator=(const optional_delete_assign_base &) = delete;
 optional_delete_assign_base &
 operator=(optional_delete_assign_base &&) noexcept = delete;
};

} // namespace detail

/// A tag type to represent an empty optional
struct nullopt_t {
  struct do_not_use {};
  constexpr explicit nullopt_t(do_not_use, do_not_use) noexcept {}
};
/// Represents an empty optional
static constexpr nullopt_t nullopt{nullopt_t::do_not_use{},
                                   nullopt_t::do_not_use{}};

class bad_optional_access : public std::exception {
public:
  bad_optional_access() = default;
  const char *what() const noexcept override { return "Optional has no value"; }
};

namespace detail {
struct i_am_secret {};
} // namespace detail

template <class T = detail::i_am_secret, class U,
 class Ret =
 detail::conditional_t<std::is_same<T, detail::i_am_secret>::value,
 detail::decay_t, T>>
constexpr optional<Ret> make_optional(U &&v);

/// An optional object is an object that contains the storage for another
/// object and manages the lifetime of this contained object, if any. The
/// contained object may be initialized after the optional object has been
/// initialized, and may be destroyed before the optional object has been
/// destroyed. The initialization state of the contained object is tracked by
/// the optional object.
template <class T>
class optional : private detail::optional_move_assign_base<T>,
 private detail::optional_delete_ctor_base<T>,
 private detail::optional_delete_assign_base<T> {
 using base = detail::optional_move_assign_base<T>;

static_assert(!std::is_same<T, in_place_t>::value,
 "instantiation of optional with in_place_t is ill-formed");
 static_assert(!std::is_same<detail::decay_t<T>, nullopt_t>::value,
 "instantiation of optional with nullopt_t is ill-formed");

template <typename L, typename R>
 friend constexpr bool operator==(const optional<L> &, const optional<R> &);

template <typename L, typename R>
 friend constexpr bool operator!=(const optional<L> &, const optional<R> &);

template <typename L, typename R>
 friend constexpr bool operator<(const optional<L> &, const optional<R> &);

template <typename L, typename R>
 friend constexpr bool operator>(const optional<L> &, const optional<R> &);

template <typename L, typename R>
 friend constexpr bool operator<=(const optional<L> &, const optional<R> &);

template <typename L, typename R>
 friend constexpr bool operator>=(const optional<L> &, const optional<R> &);

//
 template <typename L, typename R>
 friend constexpr bool operator==(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator==(const R &, const optional<T> &);

template <typename L, typename R>
 friend constexpr bool operator!=(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator!=(const R &, const optional<T> &);

template <typename L, typename R>
 friend constexpr bool operator<(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator<(const R &, const optional<T> &);

template <typename L, typename R>
 friend constexpr bool operator>(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator>(const R &, const optional<T> &);

template <typename L, typename R>
 friend constexpr bool operator<=(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator<=(const R &, const optional<T> &);

template <typename L, typename R>
 friend constexpr bool operator>=(const optional<T> &, const R &);

template <typename L, typename R>
 friend constexpr bool operator>=(const R &, const optional<T> &);

template <class Opt, class F,
 class Ret = decltype(detail::invoke(std::declval<F>(),
 *std::declval<Opt>())),
 detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
 constexpr auto optional_map_impl(Opt &&opt, F &&f) {
 return opt.hasValue()
 ? detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt))
 : optional<Ret>(nullopt);
 }

template <class Opt, class F,
 class Ret = decltype(detail::invoke(std::declval<F>(),
 *std::declval<Opt>())),
 detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
 auto optional_map_impl(Opt &&opt, F &&f) {
 if (opt.hasValue()) {
 detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt));
 return make_optional(monostate{});
 }

return optional<monostate>(nullopt);
 }

public:
// The different versions for C++14 and 11 are needed because deduced return
// types are not SFINAE-safe. This provides better support for things like
// generic lambdas. C.f.
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0826r0.html
#if defined(TL_OPTIONAL_CXX14) && !defined(TL_OPTIONAL_GCC49) && \
 !defined(TL_OPTIONAL_GCC54) && !defined(TL_OPTIONAL_GCC55)
 /// Carries out some operation which returns an optional on the stored
 /// object if there is one.
 template <class F> TL_OPTIONAL_11_CONSTEXPR auto flatMap(F &&f) & {
 using result = detail::invoke_result_t<F, T &>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : result(nullopt);
 }

template <class F> TL_OPTIONAL_11_CONSTEXPR auto flatMap(F &&f) && {
 using result = detail::invoke_result_t<F, T &&>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : result(nullopt);
 }

template <class F> constexpr auto flatMap(F &&f) const & {
 using result = detail::invoke_result_t<F, const T &>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : result(nullopt);
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F> constexpr auto flatMap(F &&f) const && {
 using result = detail::invoke_result_t<F, const T &&>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : result(nullopt);
 }
#endif
#else
 /// Carries out some operation which returns an optional on the stored
 /// object if there is one.
 template <class F>
 TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &> flatMap(F &&f) & {
 using result = detail::invoke_result_t<F, T &>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : result(nullopt);
 }

template <class F>
 TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &&> flatMap(F &&f) && {
 using result = detail::invoke_result_t<F, T &&>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : result(nullopt);
 }

template <class F>
 constexpr detail::invoke_result_t<F, const T &> flatMap(F &&f) const & {
 using result = detail::invoke_result_t<F, const T &>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : result(nullopt);
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F>
 constexpr detail::invoke_result_t<F, const T &&> flatMap(F &&f) const && {
 using result = detail::invoke_result_t<F, const T &&>;
 static_assert(detail::is_optional<result>::value,
 "F must return an optional");

return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : result(nullopt);
 }
#endif
#endif

#if defined(TL_OPTIONAL_CXX14) && !defined(TL_OPTIONAL_GCC49) && \
 !defined(TL_OPTIONAL_GCC54) && !defined(TL_OPTIONAL_GCC55)
 /// Carries out some operation on the stored object if there is one.
 template <class F> TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F> TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }

template <class F> constexpr auto map(F &&f) const & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F> constexpr auto map(F &&f) const && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }
#else
 /// Carries out some operation on the stored object if there is one.
 template <class F>
 TL_OPTIONAL_11_CONSTEXPR decltype(
 optional_map_impl(std::declval<optional &>(), std::declval<F &&>()))
 map(F &&f) & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F>
 TL_OPTIONAL_11_CONSTEXPR decltype(
 optional_map_impl(std::declval<optional &&>(), std::declval<F &&>()))
 map(F &&f) && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }

template <class F>
 constexpr decltype(optional_map_impl(std::declval<const optional &>(),
 std::declval<F &&>()))
 map(F &&f) const & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F>
 constexpr decltype(optional_map_impl(std::declval<const optional &&>(),
 std::declval<F &&>()))
 map(F &&f) const && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }
#endif
#endif

#if defined(TL_OPTIONAL_CXX14) && !defined(TL_OPTIONAL_GCC49) && \
 !defined(TL_OPTIONAL_GCC54) && !defined(TL_OPTIONAL_GCC55)
 /// Carries out some operation on the stored object if there is one.
 template <class F> TL_OPTIONAL_11_CONSTEXPR auto transform(F &&f) & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F> TL_OPTIONAL_11_CONSTEXPR auto transform(F &&f) && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }

template <class F> constexpr auto transform(F &&f) const & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F> constexpr auto transform(F &&f) const && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }
#else
 /// Carries out some operation on the stored object if there is one.
 template <class F>
 TL_OPTIONAL_11_CONSTEXPR decltype(
 optional_map_impl(std::declval<optional &>(), std::declval<F &&>()))
 transform(F &&f) & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

template <class F>
 TL_OPTIONAL_11_CONSTEXPR decltype(
 optional_map_impl(std::declval<optional &&>(), std::declval<F &&>()))
 transform(F &&f) && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }

template <class F>
 constexpr decltype(optional_map_impl(std::declval<const optional &>(),
 std::declval<F &&>()))
 transform(F &&f) const & {
 return optional_map_impl(*this, std::forward<F>(f));
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F>
 constexpr decltype(optional_map_impl(std::declval<const optional &&>(),
 std::declval<F &&>()))
 transform(F &&f) const && {
 return optional_map_impl(std::move(*this), std::forward<F>(f));
 }
#endif
#endif

/// Calls `f` if the optional is empty
 template <class F, detail::enable_if_ret_void<F> * = nullptr>
 optional<T> TL_OPTIONAL_11_CONSTEXPR orElse(F &&f) & {
 if (hasValue())
 return *this;

std::forward<F>(f)();
 return nullopt;
 }

template <class F, detail::disable_if_ret_void<F> * = nullptr>
 optional<T> TL_OPTIONAL_11_CONSTEXPR orElse(F &&f) & {
 return hasValue() ? *this : std::forward<F>(f)();
 }

template <class F, detail::enable_if_ret_void<F> * = nullptr>
 optional<T> orElse(F &&f) && {
 if (hasValue())
 return std::move(*this);

std::forward<F>(f)();
 return nullopt;
 }

template <class F, detail::disable_if_ret_void<F> * = nullptr>
 optional<T> TL_OPTIONAL_11_CONSTEXPR orElse(F &&f) && {
 return hasValue() ? std::move(*this) : std::forward<F>(f)();
 }

template <class F, detail::enable_if_ret_void<F> * = nullptr>
 optional<T> orElse(F &&f) const & {
 if (hasValue())
 return *this;

std::forward<F>(f)();
 return nullopt;
 }

template <class F, detail::disable_if_ret_void<F> * = nullptr>
 optional<T> TL_OPTIONAL_11_CONSTEXPR orElse(F &&f) const & {
 return hasValue() ? *this : std::forward<F>(f)();
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F, detail::enable_if_ret_void<F> * = nullptr>
 optional<T> orElse(F &&f) const && {
 if (hasValue())
 return std::move(*this);

std::forward<F>(f)();
 return nullopt;
 }

template <class F, detail::disable_if_ret_void<F> * = nullptr>
 optional<T> orElse(F &&f) const && {
 return hasValue() ? std::move(*this) : std::forward<F>(f)();
 }
#endif

/// Maps the stored value with `f` if there is one, otherwise returns `u`.
 template <class F, class U> U mapOr(F &&f, U &&u) & {
 return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : std::forward(u);
 }

template <class F, class U> U mapOr(F &&f, U &&u) && {
 return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : std::forward(u);
 }

template <class F, class U> U mapOr(F &&f, U &&u) const & {
 return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : std::forward(u);
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F, class U> U mapOr(F &&f, U &&u) const && {
 return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : std::forward(u);
 }
#endif

template <class P> auto filter(P &&p) & {
 return mapOr(std::forward(p), false) ? *this : nullopt;
 }

template <class P> auto filter(P &&p) && {
 return mapOr(std::forward(p), false) ? std::move(*this) : nullopt;
 }

template <class P> auto filter(P &&p) const & {
 return mapOr(std::forward(p), false) ? *this : nullopt;
 }
#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class P> optional<T> filter(P &&p) const && {
 return mapOr(std::forward(p), false) ? std::move(*this) : nullopt;
 }
#endif

/// Maps the stored value with `f` if there is one, otherwise calls
 /// `u` and returns the result.
 template <class F, class U>
 detail::invoke_result_t mapOrElse(F &&f, U &&u) & {
 return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : std::forward(u)();
 }

template <class F, class U>
 detail::invoke_result_t mapOrElse(F &&f, U &&u) && {
 return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : std::forward(u)();
 }

template <class F, class U>
 detail::invoke_result_t mapOrElse(F &&f, U &&u) const & {
 return hasValue() ? detail::invoke(std::forward<F>(f), **this)
 : std::forward(u)();
 }

#ifndef TL_OPTIONAL_NO_CONSTRR
 template <class F, class U>
 detail::invoke_result_t mapOrElse(F &&f, U &&u) const && {
 return hasValue() ? detail::invoke(std::forward<F>(f), std::move(**this))
 : std::forward(u)();
 }
#endif

/// Predicate: check if optional's value equals the given one.
 template <class F> constexpr bool containsValue(F &&f) & {
 return hasValue() ? *this == f : false;
 }

template <class F> constexpr bool containsValue(F &&f) && {
 return hasValue() ? std::move(**this) == f : false;
 }

template <class F> constexpr bool containsValue(F &&f) const & {
 return hasValue() ? *this == f : false;
 }

template <class F> constexpr bool containsValue(F &&f) const && {
 return hasValue() ? std::move(**this) == f : false;
 }

/// Returns `u` if `*this` has a value, otherwise an empty optional.
 template <class U>
 constexpr optional<typename std::decay::type> conjunction(U &&u) const {
 using result = optional<detail::decay_t>;
 return hasValue() ? result{u} : result{nullopt};
 }

/// Returns `rhs` if `*this` is empty, otherwise the current value.
  TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) & {
    return hasValue() ? *this : rhs;
  }

constexpr optional disjunction(const optional &rhs) const & {
    return hasValue() ? *this : rhs;
  }

TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) && {
    return hasValue() ? std::move(*this) : rhs;
  }

#ifndef TL_OPTIONAL_NO_CONSTRR
  constexpr optional disjunction(const optional &rhs) const && {
    return hasValue() ? std::move(*this) : rhs;
  }
#endif

TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) & {
    return hasValue() ? *this : std::move(rhs);
  }

constexpr optional disjunction(optional &&rhs) const & {
    return hasValue() ? *this : std::move(rhs);
  }

TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) && {
    return hasValue() ? std::move(*this) : std::move(rhs);
  }

#ifndef TL_OPTIONAL_NO_CONSTRR
  constexpr optional disjunction(optional &&rhs) const && {
    return hasValue() ? std::move(*this) : std::move(rhs);
  }
#endif

/// Takes the value out of the optional, leaving it empty
  optional take() {
    optional ret = std::move(*this);
    reset();
    return ret;
  }

using value_type = T;

/// Constructs an optional that does not contain a value.
  constexpr optional() noexcept = default;

constexpr optional(nullopt_t) noexcept {}

/// Copy constructor
  ///
  /// If `rhs` contains a value, the stored value is direct-initialized with
  /// it. Otherwise, the constructed optional is empty.
  TL_OPTIONAL_11_CONSTEXPR optional(const optional &rhs) = default;

/// Move constructor
  ///
  /// If `rhs` contains a value, the stored value is direct-initialized with
  /// it. Otherwise, the constructed optional is empty.
  TL_OPTIONAL_11_CONSTEXPR optional(optional &&rhs) = default;

/// Constructs the stored value in-place using the given arguments.
 template <class... Args>
 constexpr explicit optional(
 detail::enable_if_t<std::is_constructible<T, Args...>::value, in_place_t>,
 Args &&...args)
 : base(in_place, std::forward<Args>(args)...) {}

template <class U, class... Args>
 TL_OPTIONAL_11_CONSTEXPR explicit optional(
 detail::enable_if_t<std::is_constructible<T, std::initializer_list &,
 Args &&...>::value,
 in_place_t>,
 std::initializer_list il, Args &&...args) {
 this->construct(il, std::forward<Args>(args)...);
 }

/// Constructs the stored value with `u`.
 template <
 class U = T,
 detail::enable_if_t<std::is_convertible::value> * = nullptr,
 detail::enable_forward_value<T, U> * = nullptr>
 constexpr optional(U &&u) : base(in_place, std::forward(u)) {}

template <
 class U = T,
 detail::enable_if_t<!std::is_convertible::value> * = nullptr,
 detail::enable_forward_value<T, U> * = nullptr>
 constexpr explicit optional(U &&u) : base(in_place, std::forward(u)) {}

/// Converting copy constructor.
 template <
 class U, detail::enable_from_other<T, U, const U &> * = nullptr,
 detail::enable_if_t<std::is_convertible<const U &, T>::value> * = nullptr>
 optional(const optional &rhs) {
 if (rhs.hasValue()) {
 this->construct(*rhs);
 }
 }

template <class U, detail::enable_from_other<T, U, const U &> * = nullptr,
 detail::enable_if_t<!std::is_convertible<const U &, T>::value> * =
 nullptr>
 explicit optional(const optional &rhs) {
 if (rhs.hasValue()) {
 this->construct(*rhs);
 }
 }

/// Converting move constructor.
 template <
 class U, detail::enable_from_other<T, U, U &&> * = nullptr,
 detail::enable_if_t<std::is_convertible::value> * = nullptr>
 optional(optional &&rhs) {
 if (rhs.hasValue()) {
 this->construct(std::move(*rhs));
 }
 }

template <
 class U, detail::enable_from_other<T, U, U &&> * = nullptr,
 detail::enable_if_t<!std::is_convertible::value> * = nullptr>
 explicit optional(optional &&rhs) {
 if (rhs.hasValue()) {
 this->construct(std::move(*rhs));
 }
 }

/// Destroys the stored value if there is one.
  ~optional() = default;

/// Assignment to empty.
  ///
  /// Destroys the current value if there is one.
  optional &operator=(nullopt_t) noexcept {
    if (hasValue()) {
      this->m_value.~T();
      this->m_hasValue = false;
    }

return *this;
  }

/// Copy assignment.
  ///
  /// Copies the value from `rhs` if there is one. Otherwise resets the stored
  /// value in `*this`.
  optional &operator=(const optional &rhs) = default;

/// Move assignment.
  ///
  /// Moves the value from `rhs` if there is one. Otherwise resets the stored
  /// value in `*this`.
  optional &operator=(optional &&rhs) = default;

/// Assigns the stored value from `u`, destroying the old value if there was
 /// one.
 template <class U = T, detail::enable_assign_forward<T, U> * = nullptr>
 optional &operator=(U &&u) {
 if (hasValue()) {
 this->m_value = std::forward(u);
 } else {
 this->construct(std::forward(u));
 }

return *this;
  }

/// Converting copy assignment operator.
 ///
 /// Copies the value from `rhs` if there is one. Otherwise resets the stored
 /// value in `*this`.
 template <class U,
 detail::enable_assign_from_other<T, U, const U &> * = nullptr>
 optional &operator=(const optional &rhs) {
 if (hasValue()) {
 if (rhs.hasValue()) {
 this->m_value = *rhs;
 } else {
 this->hard_reset();
 }
 }

if (rhs.hasValue()) {
      this->construct(*rhs);
    }

return *this;
  }

// TODO check exception guarantee
 /// Converting move assignment operator.
 ///
 /// Moves the value from `rhs` if there is one. Otherwise resets the stored
 /// value in `*this`.
 template <class U, detail::enable_assign_from_other<T, U, U> * = nullptr>
 optional &operator=(optional &&rhs) {
 if (hasValue()) {
 if (rhs.hasValue()) {
 this->m_value = std::move(*rhs);
 } else {
 this->hard_reset();
 }
 }

if (rhs.hasValue()) {
      this->construct(std::move(*rhs));
    }

return *this;
  }

/// Constructs the value in-place, destroying the current one if there is
 /// one.
 template <class... Args> T &emplace(Args &&...args) {
 static_assert(std::is_constructible<T, Args &&...>::value,
 "T must be constructible with Args");

*this = nullopt;
 this->construct(std::forward<Args>(args)...);
 return value();
 }

template <class U, class... Args>
 detail::enable_if_t<
 std::is_constructible<T, std::initializer_list &, Args &&...>::value,
 T &>
 emplace(std::initializer_list il, Args &&...args) {
 *this = nullopt;
 this->construct(il, std::forward<Args>(args)...);
 return value();
 }

/// Swaps this optional with the other.
 ///
 /// If neither optionals have a value, nothing happens.
 /// If both have a value, the values are swapped.
 /// If one has a value, it is moved to the other and the movee is left
 /// valueless.
 void
 swap(optional &rhs) noexcept(std::is_nothrow_move_constructible<T>::value
 &&detail::is_nothrow_swappable<T>::value) {
 if (hasValue()) {
 if (rhs.hasValue()) {
 using std::swap;
 swap(**this, *rhs);
 } else {
 new (std::addressof(rhs.m_value)) T(std::move(this->m_value));
 this->m_value.T::~T();
 }
 } else if (rhs.hasValue()) {
 new (std::addressof(this->m_value)) T(std::move(rhs.m_value));
 rhs.m_value.T::~T();
 }
 }

/// Returns whether or not the optional has a value
  constexpr bool hasValue() const noexcept { return this->m_hasValue; }

constexpr explicit operator bool() const noexcept { return this->m_hasValue; }

/// Returns a pointer to the stored value
private:
  constexpr const T *operator->() const {
    return std::addressof(this->m_value);
  }

TL_OPTIONAL_11_CONSTEXPR T *operator->() {
    return std::addressof(this->m_value);
  }

/// Returns the stored value
  TL_OPTIONAL_11_CONSTEXPR T &operator*() & { return this->m_value; }

constexpr const T &operator*() const & { return this->m_value; }

TL_OPTIONAL_11_CONSTEXPR T &&operator*() && {
    return std::move(this->m_value);
  }

#ifndef TL_OPTIONAL_NO_CONSTRR
  constexpr const T &&operator*() const && { return std::move(this->m_value); }
#endif
  /// Returns the contained value if there is one, otherwise throws
  /// bad_optional_access
  TL_OPTIONAL_11_CONSTEXPR T &value() & {
    if (hasValue())
      return this->m_value;
    throw bad_optional_access();
  }
  TL_OPTIONAL_11_CONSTEXPR const T &value() const & {
    if (hasValue())
      return this->m_value;
    throw bad_optional_access();
  }
  TL_OPTIONAL_11_CONSTEXPR T &&value() && {
    if (hasValue())
      return std::move(this->m_value);
    throw bad_optional_access();
  }

#ifndef TL_OPTIONAL_NO_CONSTRR
 TL_OPTIONAL_11_CONSTEXPR const T &&value() const && {
 if (hasValue())
 return std::move(this->m_value);
 throw bad_optional_access();
 }
#endif
public:
 /// Returns the stored value if there is one, otherwise returns `u`
 template <class U> constexpr T getOr(U &&u) const & {
 static_assert(std::is_copy_constructible<T>::value &&
 std::is_convertible::value,
 "T must be copy constructible and convertible from U");
 return hasValue() ? **this : static_cast<T>(std::forward(u));
 }

template <class U> TL_OPTIONAL_11_CONSTEXPR T getOr(U &&u) && {
 static_assert(std::is_move_constructible<T>::value &&
 std::is_convertible::value,
 "T must be move constructible and convertible from U");
 return hasValue() ? **this : static_cast<T>(std::forward(u));
 }

/// Destroys the stored value if one exists, making the optional empty
  void reset() noexcept {
    if (hasValue()) {
      this->m_value.~T();
      this->m_hasValue = false;
    }
  }
}; // namespace tl

/// Compares two optional objects
template <class T, class U>
inline constexpr bool operator==(const optional<T> &lhs,
 const optional &rhs) {
 return lhs.hasValue() == rhs.hasValue() && (!lhs.hasValue() || *lhs == *rhs);
}
template <class T, class U>
inline constexpr bool operator!=(const optional<T> &lhs,
 const optional &rhs) {
 return lhs.hasValue() != rhs.hasValue() || (lhs.hasValue() && *lhs != *rhs);
}
template <class T, class U>
inline constexpr bool operator<(const optional<T> &lhs,
 const optional &rhs) {
 return rhs.hasValue() && (!lhs.hasValue() || *lhs < *rhs);
}
template <class T, class U>
inline constexpr bool operator>(const optional<T> &lhs,
 const optional &rhs) {
 return lhs.hasValue() && (!rhs.hasValue() || *lhs > *rhs);
}
template <class T, class U>
inline constexpr bool operator<=(const optional<T> &lhs,
 const optional &rhs) {
 return !lhs.hasValue() || (rhs.hasValue() && *lhs <= *rhs);
}
template <class T, class U>
inline constexpr bool operator>=(const optional<T> &lhs,
 const optional &rhs) {
 return !rhs.hasValue() || (lhs.hasValue() && *lhs >= *rhs);
}

/// Compares an optional to a `nullopt`
template <class T>
inline constexpr bool operator==(const optional<T> &lhs, nullopt_t) noexcept {
 return !lhs.hasValue();
}
template <class T>
inline constexpr bool operator==(nullopt_t, const optional<T> &rhs) noexcept {
 return !rhs.hasValue();
}
template <class T>
inline constexpr bool operator!=(const optional<T> &lhs, nullopt_t) noexcept {
 return lhs.hasValue();
}
template <class T>
inline constexpr bool operator!=(nullopt_t, const optional<T> &rhs) noexcept {
 return rhs.hasValue();
}
template <class T>
inline constexpr bool operator<(const optional<T> &, nullopt_t) noexcept {
 return false;
}
template <class T>
inline constexpr bool operator<(nullopt_t, const optional<T> &rhs) noexcept {
 return rhs.hasValue();
}
template <class T>
inline constexpr bool operator<=(const optional<T> &lhs, nullopt_t) noexcept {
 return !lhs.hasValue();
}
template <class T>
inline constexpr bool operator<=(nullopt_t, const optional<T> &) noexcept {
 return true;
}
template <class T>
inline constexpr bool operator>(const optional<T> &lhs, nullopt_t) noexcept {
 return lhs.hasValue();
}
template <class T>
inline constexpr bool operator>(nullopt_t, const optional<T> &) noexcept {
 return false;
}
template <class T>
inline constexpr bool operator>=(const optional<T> &, nullopt_t) noexcept {
 return true;
}
template <class T>
inline constexpr bool operator>=(nullopt_t, const optional<T> &rhs) noexcept {
 return !rhs.hasValue();
}

/// Compares the optional with a value.
template <class T, class U>
inline constexpr bool operator==(const optional<T> &lhs, const U &rhs) {
 return lhs.filter([&rhs](const auto value) { return value == rhs; })
 .hasValue();
}
template <class T, class U>
inline constexpr bool operator==(const U &lhs, const optional<T> &rhs) {
 return rhs == lhs;
}
template <class T, class U>
inline constexpr bool operator!=(const optional<T> &lhs, const U &rhs) {
 return !(lhs == rhs);
}
template <class T, class U>
inline constexpr bool operator!=(const U &lhs, const optional<T> &rhs) {
 return !(lhs == rhs);
}
template <class T, class U>
inline constexpr bool operator<(const optional<T> &lhs, const U &rhs) {
 return lhs.filter([&rhs](const auto value) { return value < rhs; })
 .hasValue();
}
template <class T, class U>
inline constexpr bool operator<(const U &lhs, const optional<T> &rhs) {
 return rhs.filter([&lhs](const auto value) { return lhs < value; })
 .hasValue();
}
template <class T, class U>
inline constexpr bool operator>(const optional<T> &lhs, const U &rhs) {
 return lhs.filter([&rhs](const auto value) { return value > rhs; })
 .hasValue();
}
template <class T, class U>
inline constexpr bool operator>(const U &lhs, const optional<T> &rhs) {
 return rhs.filter([&lhs](const auto value) { return lhs > value; })
 .hasValue();
}
template <class T, class U>
inline constexpr bool operator<=(const optional<T> &lhs, const U &rhs) {
 return !(lhs > rhs);
}
template <class T, class U>
inline constexpr bool operator<=(const U &lhs, const optional<T> &rhs) {
 return !(lhs > rhs);
}
template <class T, class U>
inline constexpr bool operator>=(const optional<T> &lhs, const U &rhs) {
 return !(lhs < rhs);
}
template <class T, class U>
inline constexpr bool operator>=(const U &lhs, const optional<T> &rhs) {
 return !(lhs < rhs);
}

template <class T,
 detail::enable_if_t<std::is_move_constructible<T>::value> * = nullptr,
 detail::enable_if_t<detail::is_swappable<T>::value> * = nullptr>
void swap(optional<T> &lhs,
 optional<T> &rhs) noexcept(noexcept(lhs.swap(rhs))) {
 return lhs.swap(rhs);
}

template <class T, class U, class Ret>
inline constexpr optional<Ret> make_optional(U &&v) {
 return optional<Ret>(std::forward(v));
}

template <class T, class... Args>
inline constexpr optional<T> make_optional(Args &&...args) {
 return optional<T>(in_place, std::forward<Args>(args)...);
}
template <class T, class U, class... Args>
inline constexpr optional<T> make_optional(std::initializer_list il,
 Args &&...args) {
 return optional<T>(in_place, il, std::forward<Args>(args)...);
}

#if __cplusplus >= 201703L
template <class T> optional(T) -> optional<T>;
#endif

/// Specialization for when `T` is a reference. `optional<T&>` acts similarly
/// to a `T*`, but provides more operations and shows intent more clearly.
template <class T> class optional<T &> {
 template <typename L, typename R>
 friend constexpr bool operator==(const optional<L> &, const optional<R> &);