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ulib/3party/optional/optional.h

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feat update add optional.hpp
2024-01-05 12:29:53 +08:00
///
// optional - An implementation of std::optional with extensions
// Written in 2017 by Sy Brand (tartanllama@gmail.com, @TartanLlama)
//
// Documentation available at https://tl.tartanllama.xyz/
//
// 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 1
#define TL_OPTIONAL_VERSION_MINOR 1
#define TL_OPTIONAL_VERSION_PATCH 0
#include <exception>
#include <functional>
#include <memory>
#include <new>
#include <type_traits>
#include <utility>
#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> : 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_TRAITS_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_TRAITS_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_TRAITS_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<U &>()))>
std::true_type can_swap(int) noexcept(noexcept(swap(std::declval<T &>(),
std::declval<U &>())));
template<class, class>
std::false_type uses_std(...);
template<class T, class U>
std::is_same<decltype(swap(std::declval<T &>(), std::declval<U &>())), 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<U>::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<U>, in_place_t>::value
&& !std::is_same<optional<T>, detail::decay_t<U>>::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<U> &>::value
&& !std::is_constructible<T, optional<U> &&>::value
&& !std::is_constructible<T, const optional<U> &>::value
&& !std::is_constructible<T, const optional<U> &&>::value
&& !std::is_convertible<optional<U> &, T>::value
&& !std::is_convertible<optional<U> &&, T>::value
&& !std::is_convertible<const optional<U> &, T>::value
&& !std::is_convertible<const optional<U> &&, T>::value>;
template<class T, class U>
using enable_assign_forward = detail::enable_if_t<
!std::is_same<optional<T>, detail::decay_t<U>>::value
&& !detail::conjunction<std::is_scalar<T>,
std::is_same<T, detail::decay_t<U>>>::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<U> &>::value
&& !std::is_constructible<T, optional<U> &&>::value
&& !std::is_constructible<T, const optional<U> &>::value
&& !std::is_constructible<T, const optional<U> &&>::value
&& !std::is_convertible<optional<U> &, T>::value
&& !std::is_convertible<optional<U> &&, T>::value
&& !std::is_convertible<const optional<U> &, T>::value
&& !std::is_convertible<const optional<U> &&, T>::value
&& !std::is_assignable<T &, optional<U> &>::value
&& !std::is_assignable<T &, optional<U> &&>::value
&& !std::is_assignable<T &, const optional<U> &>::value
&& !std::is_assignable<T &, const optional<U> &&>::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(),
m_has_value(false)
{}
template<class... U>
TL_OPTIONAL_11_CONSTEXPR optional_storage_base(in_place_t, U &&...u)
: m_value(std::forward<U>(u)...),
m_has_value(true)
{}
~optional_storage_base()
{
if (m_has_value) {
m_value.~T();
m_has_value = false;
}
}
struct dummy {};
union {
dummy m_dummy;
T m_value;
};
bool m_has_value;
};
// 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(),
m_has_value(false)
{}
template<class... U>
TL_OPTIONAL_11_CONSTEXPR optional_storage_base(in_place_t, U &&...u)
: m_value(std::forward<U>(u)...),
m_has_value(true)
{}
// No destructor, so this class is trivially destructible
struct dummy {};
union {
dummy m_dummy;
T m_value;
};
bool m_has_value = 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_has_value = false;
}
template<class... Args>
void construct(Args &&...args)
{
new (std::addressof(this->m_value)) T(std::forward<Args>(args)...);
this->m_has_value = true;
}
template<class Opt>
void assign(Opt &&rhs)
{
if (this->has_value()) {
if (rhs.has_value()) {
this->m_value = std::forward<Opt>(rhs).get();
} else {
this->m_value.~T();
this->m_has_value = false;
}
}
else if (rhs.has_value()) {
construct(std::forward<Opt>(rhs).get());
}
}
bool has_value() const { return this->m_has_value; }
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)
: optional_operations_base<T>()
{
if (rhs.has_value()) {
this->construct(rhs.get());
} else {
this->m_has_value = 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.has_value()) {
this->construct(std::move(rhs.get()));
} else {
this->m_has_value = 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 { return "Optional has no value"; }
};
/// 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");
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 and_then(F &&f) &
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR auto and_then(F &&f) &&
{
using result = detail::invoke_result_t<F, T &&>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: result(nullopt);
}
template<class F>
constexpr auto and_then(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 has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F>
constexpr auto and_then(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 has_value()
? 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 &> and_then(F &&f) &
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &&> and_then(F &&f) &&
{
using result = detail::invoke_result_t<F, T &&>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: result(nullopt);
}
template<class F>
constexpr detail::invoke_result_t<F, const T &> and_then(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 has_value() ? 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 &&> and_then(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 has_value()
? 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 or_else(F &&f) &
{
if (has_value()) return *this;
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> TL_OPTIONAL_11_CONSTEXPR or_else(F &&f) &
{
return has_value() ? *this : std::forward<F>(f)();
}
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) &&
{
if (has_value()) 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 or_else(F &&f) &&
{
return has_value() ? std::move(*this) : std::forward<F>(f)();
}
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &
{
if (has_value()) return *this;
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> TL_OPTIONAL_11_CONSTEXPR or_else(F &&f) const &
{
return has_value() ? *this : std::forward<F>(f)();
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &&
{
if (has_value()) return std::move(*this);
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &&
{
return has_value() ? 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 map_or(F &&f, U &&u) &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u);
}
template<class F, class U>
U map_or(F &&f, U &&u) &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u);
}
template<class F, class U>
U map_or(F &&f, U &&u) const &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, class U>
U map_or(F &&f, U &&u) const &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u);
}
#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<U> map_or_else(F &&f, U &&u) &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u)();
}
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u)();
}
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) const &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u)();
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) const &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u)();
}
#endif
/// Returns `u` if `*this` has a value, otherwise an empty optional.
template<class U>
constexpr optional<typename std::decay<U>::type> conjunction(U &&u) const
{
using result = optional<detail::decay_t<U>>;
return has_value() ? result{u} : result{nullopt};
}
/// Returns `rhs` if `*this` is empty, otherwise the current value.
TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) &
{
return has_value() ? *this : rhs;
}
constexpr optional disjunction(const optional &rhs) const &
{
return has_value() ? *this : rhs;
}
TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) &&
{
return has_value() ? std::move(*this) : rhs;
}
#ifndef TL_OPTIONAL_NO_CONSTRR
constexpr optional disjunction(const optional &rhs) const &&
{
return has_value() ? std::move(*this) : rhs;
}
#endif
TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) &
{
return has_value() ? *this : std::move(rhs);
}
constexpr optional disjunction(optional &&rhs) const &
{
return has_value() ? *this : std::move(rhs);
}
TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) &&
{
return has_value() ? std::move(*this) : std::move(rhs);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
constexpr optional disjunction(optional &&rhs) const &&
{
return has_value() ? 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<U> &,
Args &&...>::value,
in_place_t>,
std::initializer_list<U> 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<U &&, T>::value> * = nullptr,
detail::enable_forward_value<T, U> * = nullptr>
constexpr optional(U &&u) : base(in_place, std::forward<U>(u))
{}
template<
class U = T,
detail::enable_if_t<!std::is_convertible<U &&, T>::value> * = nullptr,
detail::enable_forward_value<T, U> * = nullptr>
constexpr explicit optional(U &&u) : base(in_place, std::forward<U>(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<U> &rhs)
{
if (rhs.has_value()) { 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<U> &rhs)
{
if (rhs.has_value()) { this->construct(*rhs); }
}
/// Converting move constructor.
template<
class U,
detail::enable_from_other<T, U, U &&> * = nullptr,
detail::enable_if_t<std::is_convertible<U &&, T>::value> * = nullptr>
optional(optional<U> &&rhs)
{
if (rhs.has_value()) { this->construct(std::move(*rhs)); }
}
template<
class U,
detail::enable_from_other<T, U, U &&> * = nullptr,
detail::enable_if_t<!std::is_convertible<U &&, T>::value> * = nullptr>
explicit optional(optional<U> &&rhs)
{
if (rhs.has_value()) { 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 (has_value()) {
this->m_value.~T();
this->m_has_value = 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 (has_value()) {
this->m_value = std::forward<U>(u);
} else {
this->construct(std::forward<U>(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<U> &rhs)
{
if (has_value()) {
if (rhs.has_value()) {
this->m_value = *rhs;
} else {
this->hard_reset();
}
}
else if (rhs.has_value()) {
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<U> &&rhs)
{
if (has_value()) {
if (rhs.has_value()) {
this->m_value = std::move(*rhs);
} else {
this->hard_reset();
}
}
else if (rhs.has_value()) {
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<U> &, Args &&...>::value,
T &>
emplace(std::initializer_list<U> 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)
{
using std::swap;
if (has_value()) {
if (rhs.has_value()) {
swap(**this, *rhs);
} else {
new (std::addressof(rhs.m_value)) T(std::move(this->m_value));
this->m_value.T::~T();
}
} else if (rhs.has_value()) {
new (std::addressof(this->m_value)) T(std::move(rhs.m_value));
rhs.m_value.T::~T();
}
swap(this->m_has_value, rhs.m_has_value);
}
/// Returns a pointer to the stored value
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 whether or not the optional has a value
constexpr bool has_value() const noexcept { return this->m_has_value; }
constexpr explicit operator bool() const noexcept
{
return this->m_has_value;
}
/// Returns the contained value if there is one, otherwise throws bad_optional_access
TL_OPTIONAL_11_CONSTEXPR T &value() &
{
if (has_value()) return this->m_value;
throw bad_optional_access();
}
TL_OPTIONAL_11_CONSTEXPR const T &value() const &
{
if (has_value()) return this->m_value;
throw bad_optional_access();
}
TL_OPTIONAL_11_CONSTEXPR T &&value() &&
{
if (has_value()) return std::move(this->m_value);
throw bad_optional_access();
}
#ifndef TL_OPTIONAL_NO_CONSTRR
TL_OPTIONAL_11_CONSTEXPR const T &&value() const &&
{
if (has_value()) return std::move(this->m_value);
throw bad_optional_access();
}
#endif
/// Returns the stored value if there is one, otherwise returns `u`
template<class U>
constexpr T value_or(U &&u) const &
{
static_assert(std::is_copy_constructible<T>::value
&& std::is_convertible<U &&, T>::value,
"T must be copy constructible and convertible from U");
return has_value() ? **this : static_cast<T>(std::forward<U>(u));
}
template<class U>
TL_OPTIONAL_11_CONSTEXPR T value_or(U &&u) &&
{
static_assert(std::is_move_constructible<T>::value
&& std::is_convertible<U &&, T>::value,
"T must be move constructible and convertible from U");
return has_value() ? std::move(**this)
: static_cast<T>(std::forward<U>(u));
}
/// Destroys the stored value if one exists, making the optional empty
void reset() noexcept
{
if (has_value()) {
this->m_value.~T();
this->m_has_value = false;
}
}
};// namespace tl
/// Compares two optional objects
template<class T, class U>
inline constexpr bool
operator==(const optional<T> &lhs, const optional<U> &rhs)
{
return lhs.has_value() == rhs.has_value()
&& (!lhs.has_value() || *lhs == *rhs);
}
template<class T, class U>
inline constexpr bool
operator!=(const optional<T> &lhs, const optional<U> &rhs)
{
return lhs.has_value() != rhs.has_value()
|| (lhs.has_value() && *lhs != *rhs);
}
template<class T, class U>
inline constexpr bool
operator<(const optional<T> &lhs, const optional<U> &rhs)
{
return rhs.has_value() && (!lhs.has_value() || *lhs < *rhs);
}
template<class T, class U>
inline constexpr bool
operator>(const optional<T> &lhs, const optional<U> &rhs)
{
return lhs.has_value() && (!rhs.has_value() || *lhs > *rhs);
}
template<class T, class U>
inline constexpr bool
operator<=(const optional<T> &lhs, const optional<U> &rhs)
{
return !lhs.has_value() || (rhs.has_value() && *lhs <= *rhs);
}
template<class T, class U>
inline constexpr bool
operator>=(const optional<T> &lhs, const optional<U> &rhs)
{
return !rhs.has_value() || (lhs.has_value() && *lhs >= *rhs);
}
/// Compares an optional to a `nullopt`
template<class T>
inline constexpr bool
operator==(const optional<T> &lhs, nullopt_t) noexcept
{
return !lhs.has_value();
}
template<class T>
inline constexpr bool
operator==(nullopt_t, const optional<T> &rhs) noexcept
{
return !rhs.has_value();
}
template<class T>
inline constexpr bool
operator!=(const optional<T> &lhs, nullopt_t) noexcept
{
return lhs.has_value();
}
template<class T>
inline constexpr bool
operator!=(nullopt_t, const optional<T> &rhs) noexcept
{
return rhs.has_value();
}
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.has_value();
}
template<class T>
inline constexpr bool
operator<=(const optional<T> &lhs, nullopt_t) noexcept
{
return !lhs.has_value();
}
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.has_value();
}
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.has_value();
}
/// Compares the optional with a value.
template<class T, class U>
inline constexpr bool
operator==(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs == rhs : false;
}
template<class T, class U>
inline constexpr bool
operator==(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs == *rhs : false;
}
template<class T, class U>
inline constexpr bool
operator!=(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs != rhs : true;
}
template<class T, class U>
inline constexpr bool
operator!=(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs != *rhs : true;
}
template<class T, class U>
inline constexpr bool
operator<(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs < rhs : true;
}
template<class T, class U>
inline constexpr bool
operator<(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs < *rhs : false;
}
template<class T, class U>
inline constexpr bool
operator<=(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs <= rhs : true;
}
template<class T, class U>
inline constexpr bool
operator<=(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs <= *rhs : false;
}
template<class T, class U>
inline constexpr bool
operator>(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs > rhs : false;
}
template<class T, class U>
inline constexpr bool
operator>(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs > *rhs : true;
}
template<class T, class U>
inline constexpr bool
operator>=(const optional<T> &lhs, const U &rhs)
{
return lhs.has_value() ? *lhs >= rhs : false;
}
template<class T, class U>
inline constexpr bool
operator>=(const U &lhs, const optional<T> &rhs)
{
return rhs.has_value() ? lhs >= *rhs : true;
}
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);
}
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<U>,
T>>
inline constexpr optional<Ret>
make_optional(U &&v)
{
return optional<Ret>(std::forward<U>(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<U> il, Args &&...args)
{
return optional<T>(in_place, il, std::forward<Args>(args)...);
}
#if __cplusplus >= 201703L
template<class T>
optional(T) -> optional<T>;
#endif
/// \exclude
namespace detail {
#ifdef TL_OPTIONAL_CXX14
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.has_value()
? 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.has_value()) {
detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt));
return make_optional(monostate{});
}
return optional<monostate>(nullopt);
}
#else
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) -> optional<Ret>
{
return opt.has_value()
? 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) -> optional<monostate>
{
if (opt.has_value()) {
detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt));
return monostate{};
}
return nullopt;
}
#endif
}// namespace detail
/// 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 &> {
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 and_then(F &&f) &
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR auto and_then(F &&f) &&
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
constexpr auto and_then(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 has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F>
constexpr auto and_then(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 has_value() ? detail::invoke(std::forward<F>(f), **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 &> and_then(F &&f) &
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &> and_then(F &&f) &&
{
using result = detail::invoke_result_t<F, T &>;
static_assert(detail::is_optional<result>::value,
"F must return an optional");
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: result(nullopt);
}
template<class F>
constexpr detail::invoke_result_t<F, const T &> and_then(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 has_value() ? 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 &> and_then(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 has_value()
? 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 detail::optional_map_impl(*this, std::forward<F>(f));
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) &&
{
return detail::optional_map_impl(std::move(*this), std::forward<F>(f));
}
template<class F>
constexpr auto map(F &&f) const &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
template<class F>
constexpr auto map(F &&f) const &&
{
return detail::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(detail::optional_map_impl(
std::declval<optional &>(),
std::declval<F &&>()))
map(F &&f) &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR decltype(detail::optional_map_impl(
std::declval<optional &&>(),
std::declval<F &&>()))
map(F &&f) &&
{
return detail::optional_map_impl(std::move(*this), std::forward<F>(f));
}
template<class F>
constexpr decltype(detail::optional_map_impl(
std::declval<const optional &>(),
std::declval<F &&>()))
map(F &&f) const &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F>
constexpr decltype(detail::optional_map_impl(
std::declval<const optional &&>(),
std::declval<F &&>()))
map(F &&f) const &&
{
return detail::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 detail::optional_map_impl(*this, std::forward<F>(f));
}
template<class F>
TL_OPTIONAL_11_CONSTEXPR auto transform(F &&f) &&
{
return detail::optional_map_impl(std::move(*this), std::forward<F>(f));
}
template<class F>
constexpr auto transform(F &&f) const &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
template<class F>
constexpr auto transform(F &&f) const &&
{
return detail::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(detail::optional_map_impl(
std::declval<optional &>(),
std::declval<F &&>()))
transform(F &&f) &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
/// \group map
/// \synopsis template <class F> auto transform(F &&f) &&;
template<class F>
TL_OPTIONAL_11_CONSTEXPR decltype(detail::optional_map_impl(
std::declval<optional &&>(),
std::declval<F &&>()))
transform(F &&f) &&
{
return detail::optional_map_impl(std::move(*this), std::forward<F>(f));
}
template<class F>
constexpr decltype(detail::optional_map_impl(
std::declval<const optional &>(),
std::declval<F &&>()))
transform(F &&f) const &
{
return detail::optional_map_impl(*this, std::forward<F>(f));
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F>
constexpr decltype(detail::optional_map_impl(
std::declval<const optional &&>(),
std::declval<F &&>()))
transform(F &&f) const &&
{
return detail::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 or_else(F &&f) &
{
if (has_value()) return *this;
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> TL_OPTIONAL_11_CONSTEXPR or_else(F &&f) &
{
return has_value() ? *this : std::forward<F>(f)();
}
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) &&
{
if (has_value()) 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 or_else(F &&f) &&
{
return has_value() ? std::move(*this) : std::forward<F>(f)();
}
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &
{
if (has_value()) return *this;
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> TL_OPTIONAL_11_CONSTEXPR or_else(F &&f) const &
{
return has_value() ? *this : std::forward<F>(f)();
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, detail::enable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &&
{
if (has_value()) return std::move(*this);
std::forward<F>(f)();
return nullopt;
}
template<class F, detail::disable_if_ret_void<F> * = nullptr>
optional<T> or_else(F &&f) const &&
{
return has_value() ? 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 map_or(F &&f, U &&u) &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u);
}
template<class F, class U>
U map_or(F &&f, U &&u) &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u);
}
template<class F, class U>
U map_or(F &&f, U &&u) const &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, class U>
U map_or(F &&f, U &&u) const &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u);
}
#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<U> map_or_else(F &&f, U &&u) &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u)();
}
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u)();
}
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) const &
{
return has_value() ? detail::invoke(std::forward<F>(f), **this)
: std::forward<U>(u)();
}
#ifndef TL_OPTIONAL_NO_CONSTRR
template<class F, class U>
detail::invoke_result_t<U> map_or_else(F &&f, U &&u) const &&
{
return has_value()
? detail::invoke(std::forward<F>(f), std::move(**this))
: std::forward<U>(u)();
}
#endif
/// Returns `u` if `*this` has a value, otherwise an empty optional.
template<class U>
constexpr optional<typename std::decay<U>::type> conjunction(U &&u) const
{
using result = optional<detail::decay_t<U>>;
return has_value() ? result{u} : result{nullopt};
}
/// Returns `rhs` if `*this` is empty, otherwise the current value.
TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) &
{
return has_value() ? *this : rhs;
}
constexpr optional disjunction(const optional &rhs) const &
{
return has_value() ? *this : rhs;
}
TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) &&
{
return has_value() ? std::move(*this) : rhs;
}
#ifndef TL_OPTIONAL_NO_CONSTRR
constexpr optional disjunction(const optional &rhs) const &&
{
return has_value() ? std::move(*this) : rhs;
}
#endif
TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) &
{
return has_value() ? *this : std::move(rhs);
}
constexpr optional disjunction(optional &&rhs) const &
{
return has_value() ? *this : std::move(rhs);
}
TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) &&
{
return has_value() ? std::move(*this) : std::move(rhs);
}
#ifndef TL_OPTIONAL_NO_CONSTRR
constexpr optional disjunction(optional &&rhs) const &&
{
return has_value() ? 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 : m_value(nullptr) {}
constexpr optional(nullopt_t) noexcept : m_value(nullptr) {}
/// 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) noexcept = 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 with `u`.
template<class U = T,
detail::enable_if_t<
!detail::is_optional<detail::decay_t<U>>::value> * = nullptr>
constexpr optional(U &&u) noexcept : m_value(std::addressof(u))
{
static_assert(std::is_lvalue_reference<U>::value,
"U must be an lvalue");
}
template<class U>
constexpr explicit optional(const optional<U> &rhs) noexcept
: optional(*rhs)
{}
/// No-op
~optional() = default;
/// Assignment to empty.
///
/// Destroys the current value if there is one.
optional &operator=(nullopt_t) noexcept
{
m_value = nullptr;
return *this;
}
/// Copy assignment.
///
/// Rebinds this optional to the referee of `rhs` if there is one. Otherwise
/// resets the stored value in `*this`.
optional &operator=(const optional &rhs) = default;
/// Rebinds this optional to `u`.
template<class U = T,
detail::enable_if_t<
!detail::is_optional<detail::decay_t<U>>::value> * = nullptr>
optional &operator=(U &&u)
{
static_assert(std::is_lvalue_reference<U>::value,
"U must be an lvalue");
m_value = std::addressof(u);
return *this;
}
/// Converting copy assignment operator.
///
/// Rebinds this optional to the referee of `rhs` if there is one. Otherwise
/// resets the stored value in `*this`.
template<class U>
optional &operator=(const optional<U> &rhs) noexcept
{
m_value = std::addressof(rhs.value());
return *this;
}
/// Rebinds this optional to `u`.
template<class U = T,
detail::enable_if_t<
!detail::is_optional<detail::decay_t<U>>::value> * = nullptr>
optional &emplace(U &&u) noexcept
{
return *this = std::forward<U>(u);
}
void swap(optional &rhs) noexcept { std::swap(m_value, rhs.m_value); }
/// Returns a pointer to the stored value
constexpr const T *operator->() const noexcept { return m_value; }
TL_OPTIONAL_11_CONSTEXPR T *operator->() noexcept { return m_value; }
/// Returns the stored value
TL_OPTIONAL_11_CONSTEXPR T &operator*() noexcept { return *m_value; }
constexpr const T &operator*() const noexcept { return *m_value; }
constexpr bool has_value() const noexcept { return m_value != nullptr; }
constexpr explicit operator bool() const noexcept
{
return m_value != nullptr;
}
/// Returns the contained value if there is one, otherwise throws bad_optional_access
TL_OPTIONAL_11_CONSTEXPR T &value()
{
if (has_value()) return *m_value;
throw bad_optional_access();
}
TL_OPTIONAL_11_CONSTEXPR const T &value() const
{
if (has_value()) return *m_value;
throw bad_optional_access();
}
/// Returns the stored value if there is one, otherwise returns `u`
template<class U>
constexpr T value_or(U &&u) const & noexcept
{
static_assert(std::is_copy_constructible<T>::value
&& std::is_convertible<U &&, T>::value,
"T must be copy constructible and convertible from U");
return has_value() ? **this : static_cast<T>(std::forward<U>(u));
}
/// \group value_or
template<class U>
TL_OPTIONAL_11_CONSTEXPR T value_or(U &&u) && noexcept
{
static_assert(std::is_move_constructible<T>::value
&& std::is_convertible<U &&, T>::value,
"T must be move constructible and convertible from U");
return has_value() ? **this : static_cast<T>(std::forward<U>(u));
}
/// Destroys the stored value if one exists, making the optional empty
void reset() noexcept { m_value = nullptr; }
private:
T *m_value;
};// namespace tl
}// namespace tl
namespace std {
// TODO SFINAE
template<class T>
struct hash<tl::optional<T>> {
::std::size_t operator()(const tl::optional<T> &o) const
{
if (!o.has_value()) return 0;
return std::hash<tl::detail::remove_const_t<T>>()(*o);
}
};
// if <= C++14
#if __cplusplus < 201703L
template<typename T>
using optional = tl::optional<T>;
template<typename T>
using nullopt_t = tl::nullopt_t;
// make_optional
template<typename T>
constexpr tl::optional<tl::detail::decay_t<T>>
make_optional(T &&v)
{
return tl::make_optional(std::forward<T>(v));
}
template<typename T, typename... Args>
constexpr tl::optional<T>
make_optional(Args &&...args)
{
return tl::make_optional<T>(std::forward<Args>(args)...);
}
template<typename T, typename U, typename... Args>
constexpr tl::optional<T>
make_optional(std::initializer_list<U> il, Args &&...args)
{
return tl::make_optional<T>(il, std::forward<Args>(args)...);
}
constexpr tl::nullopt_t nullopt{tl::nullopt};
#endif
}// namespace std
#endif
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