Squashed 'third_party/optional/' content from commit 1baad184f
Change-Id: I9b2473a84dcf6d9892f1f7a9fd21b340796b6ff5
git-subtree-dir: third_party/optional
git-subtree-split: 1baad184f022a3a7502db094a984a86adedf9626
diff --git a/tl/optional.hpp b/tl/optional.hpp
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+++ b/tl/optional.hpp
@@ -0,0 +1,2352 @@
+
+///
+// optional - An implementation of std::optional with extensions
+// Written in 2017 by Simon Brand (@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 <exception>
+#include <functional>
+#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
+ }
+}
+#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))
+/// \exclude
+#define TL_OPTIONAL_11_CONSTEXPR
+#else
+/// \exclude
+#define TL_OPTIONAL_11_CONSTEXPR constexpr
+#endif
+
+namespace tl {
+#ifndef TL_MONOSTATE_INPLACE_MUTEX
+#define TL_MONOSTATE_INPLACE_MUTEX
+/// \brief Used to represent an optional with no data; essentially a bool
+class monostate {};
+
+/// \brief A tag type to tell optional to construct its value in-place
+struct in_place_t {
+ explicit in_place_t() = default;
+};
+/// \brief A tag to tell optional to construct its value in-place
+static constexpr in_place_t in_place{};
+#endif
+
+template <class T> class optional;
+
+/// \exclude
+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_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;
+#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>;
+
+#ifdef _MSC_VER
+// TODO make a version which works with MSVC
+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
+
+// 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) noexcept {
+ 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) {
+ 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
+
+/// \brief 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 {}
+};
+/// \brief Represents an empty optional
+/// \synopsis static constexpr nullopt_t nullopt;
+///
+/// *Examples*:
+/// ```
+/// tl::optional<int> a = tl::nullopt;
+/// void foo (tl::optional<int>);
+/// foo(tl::nullopt); //pass 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)
+ /// \group and_then
+ /// Carries out some operation which returns an optional on the stored
+ /// object if there is one. \requires `std::invoke(std::forward<F>(f),
+ /// value())` returns a `std::optional<U>` for some `U`. \returns Let `U` be
+ /// the result of `std::invoke(std::forward<F>(f), value())`. Returns a
+ /// `std::optional<U>`. The return value is empty if `*this` is empty,
+ /// otherwise the return value of `std::invoke(std::forward<F>(f), value())`
+ /// is returned.
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
+ 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
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
+ 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
+ /// \group and_then
+ /// Carries out some operation which returns an optional on the stored
+ /// object if there is one. \requires `std::invoke(std::forward<F>(f),
+ /// value())` returns a `std::optional<U>` for some `U`.
+ /// \returns Let `U` be the result of `std::invoke(std::forward<F>(f),
+ /// value())`. Returns a `std::optional<U>`. The return value is empty if
+ /// `*this` is empty, otherwise the return value of
+ /// `std::invoke(std::forward<F>(f), value())` is returned.
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
+ 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
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
+ 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)
+ /// \brief Carries out some operation on the stored object if there is one.
+ /// \returns Let `U` be the result of `std::invoke(std::forward<F>(f),
+ /// value())`. Returns a `std::optional<U>`. The return value is empty if
+ /// `*this` is empty, otherwise an `optional<U>` is constructed from the
+ /// return value of `std::invoke(std::forward<F>(f), value())` and is
+ /// returned.
+ ///
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) &;
+ template <class F> TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) & {
+ return optional_map_impl(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) &&;
+ template <class F> TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) && {
+ return optional_map_impl(std::move(*this), std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) const&;
+ template <class F> constexpr auto map(F &&f) const & {
+ return optional_map_impl(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) const&&;
+ template <class F> constexpr auto map(F &&f) const && {
+ return optional_map_impl(std::move(*this), std::forward<F>(f));
+ }
+#else
+ /// \brief Carries out some operation on the stored object if there is one.
+ /// \returns Let `U` be the result of `std::invoke(std::forward<F>(f),
+ /// value())`. Returns a `std::optional<U>`. The return value is empty if
+ /// `*this` is empty, otherwise an `optional<U>` is constructed from the
+ /// return value of `std::invoke(std::forward<F>(f), value())` and is
+ /// returned.
+ ///
+ /// \group map
+ /// \synopsis template <class F> auto map(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(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> auto map(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));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> auto map(F &&f) const&;
+ 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
+ /// \group map
+ /// \synopsis template <class F> auto map(F &&f) const&&;
+ 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
+
+ /// \brief Calls `f` if the optional is empty
+ /// \requires `std::invoke_result_t<F>` must be void or convertible to
+ /// `optional<T>`.
+ /// \effects If `*this` has a value, returns `*this`.
+ /// Otherwise, if `f` returns `void`, calls `std::forward<F>(f)` and returns
+ /// `std::nullopt`. Otherwise, returns `std::forward<F>(f)()`.
+ ///
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (F &&f) &;
+ 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;
+ }
+
+ /// \exclude
+ 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)();
+ }
+
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (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;
+ }
+
+ /// \exclude
+ 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)();
+ }
+
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (F &&f) const &;
+ 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;
+ }
+
+ /// \exclude
+ 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
+ /// \exclude
+ 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;
+ }
+
+ /// \exclude
+ 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
+
+ /// \brief Maps the stored value with `f` if there is one, otherwise returns
+ /// `u`.
+ ///
+ /// \details If there is a value stored, then `f` is called with `**this`
+ /// and the value is returned. Otherwise `u` is returned.
+ ///
+ /// \group map_or
+ 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);
+ }
+
+ /// \group map_or
+ 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);
+ }
+
+ /// \group map_or
+ 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
+ /// \group map_or
+ 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
+
+ /// \brief Maps the stored value with `f` if there is one, otherwise calls
+ /// `u` and returns the result.
+ ///
+ /// \details If there is a value stored, then `f` is
+ /// called with `**this` and the value is returned. Otherwise
+ /// `std::forward<U>(u)()` is returned.
+ ///
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, 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), **this)
+ : std::forward<U>(u)();
+ }
+
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, 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)();
+ }
+
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, U &&u)
+ /// const &;
+ 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
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, U &&u)
+ /// const &&;
+ 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.
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) & {
+ return has_value() ? *this : rhs;
+ }
+
+ /// \group disjunction
+ constexpr optional disjunction(const optional &rhs) const & {
+ return has_value() ? *this : rhs;
+ }
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) && {
+ return has_value() ? std::move(*this) : rhs;
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group disjunction
+ constexpr optional disjunction(const optional &rhs) const && {
+ return has_value() ? std::move(*this) : rhs;
+ }
+#endif
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) & {
+ return has_value() ? *this : std::move(rhs);
+ }
+
+ /// \group disjunction
+ constexpr optional disjunction(optional &&rhs) const & {
+ return has_value() ? *this : std::move(rhs);
+ }
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) && {
+ return has_value() ? std::move(*this) : std::move(rhs);
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group disjunction
+ 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
+ /// \group take
+ optional take() & {
+ optional ret = *this;
+ reset();
+ return ret;
+ }
+
+ /// \group take
+ optional take() const & {
+ optional ret = *this;
+ reset();
+ return ret;
+ }
+
+ /// \group take
+ optional take() && {
+ optional ret = std::move(*this);
+ reset();
+ return ret;
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group take
+ optional take() const && {
+ optional ret = std::move(*this);
+ reset();
+ return ret;
+ }
+#endif
+
+ using value_type = T;
+
+ /// Constructs an optional that does not contain a value.
+ /// \group ctor_empty
+ constexpr optional() noexcept = default;
+
+ /// \group ctor_empty
+ 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.
+ /// \group in_place
+ /// \synopsis template <class... Args> constexpr explicit optional(in_place_t, Args&&... args);
+ 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)...) {}
+
+ /// \group in_place
+ /// \synopsis template <class U, class... Args>\nconstexpr explicit optional(in_place_t, std::initializer_list<U>&, 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`.
+ /// \synopsis template <class U=T> constexpr optional(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 optional(U &&u) : base(in_place, std::forward<U>(u)) {}
+
+ /// \exclude
+ 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.
+ /// \synopsis template <class U> optional(const optional<U> &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>
+ optional(const optional<U> &rhs) {
+ this->construct(*rhs);
+ }
+
+ /// \exclude
+ 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) {
+ this->construct(*rhs);
+ }
+
+ /// Converting move constructor.
+ /// \synopsis template <class U> optional(optional<U> &&rhs);
+ 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) {
+ this->construct(std::move(*rhs));
+ }
+
+ /// \exclude
+ 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) {
+ 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.
+ /// \synopsis optional &operator=(U &&u);
+ 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`.
+ /// \synopsis optional &operator=(const optional<U> & rhs);
+ 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();
+ }
+ }
+
+ 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`.
+ /// \synopsis optional &operator=(optional<U> && rhs);
+ 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();
+ }
+ }
+
+ if (rhs.has_value()) {
+ this->construct(std::move(*rhs));
+ }
+
+ return *this;
+ }
+
+ /// Constructs the value in-place, destroying the current one if there is
+ /// one.
+ /// \group emplace
+ 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();
+ }
+
+ /// \group emplace
+ /// \synopsis template <class U, class... Args>\nT& emplace(std::initializer_list<U> il, Args &&... args);
+ 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) {
+ if (has_value()) {
+ if (rhs.has_value()) {
+ 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.has_value()) {
+ new (std::addressof(this->m_value)) T(std::move(rhs.m_value));
+ rhs.m_value.T::~T();
+ }
+ }
+
+ /// \returns a pointer to the stored value
+ /// \requires a value is stored
+ /// \group pointer
+ /// \synopsis constexpr const T *operator->() const;
+ constexpr const T *operator->() const {
+ return std::addressof(this->m_value);
+ }
+
+ /// \group pointer
+ /// \synopsis constexpr T *operator->();
+ TL_OPTIONAL_11_CONSTEXPR T *operator->() {
+ return std::addressof(this->m_value);
+ }
+
+ /// \returns the stored value
+ /// \requires a value is stored
+ /// \group deref
+ /// \synopsis constexpr T &operator*();
+ TL_OPTIONAL_11_CONSTEXPR T &operator*() & { return this->m_value; }
+
+ /// \group deref
+ /// \synopsis constexpr const T &operator*() const;
+ constexpr const T &operator*() const & { return this->m_value; }
+
+ /// \exclude
+ TL_OPTIONAL_11_CONSTEXPR T &&operator*() && {
+ return std::move(this->m_value);
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \exclude
+ constexpr const T &&operator*() const && { return std::move(this->m_value); }
+#endif
+
+ /// \returns whether or not the optional has a value
+ /// \group has_value
+ constexpr bool has_value() const noexcept { return this->m_has_value; }
+
+ /// \group 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]
+ /// \group value
+ /// \synopsis constexpr T &value();
+ TL_OPTIONAL_11_CONSTEXPR T &value() & {
+ if (has_value())
+ return this->m_value;
+ throw bad_optional_access();
+ }
+ /// \group value
+ /// \synopsis constexpr const T &value() const;
+ TL_OPTIONAL_11_CONSTEXPR const T &value() const & {
+ if (has_value())
+ return this->m_value;
+ throw bad_optional_access();
+ }
+ /// \exclude
+ TL_OPTIONAL_11_CONSTEXPR T &&value() && {
+ if (has_value())
+ return std::move(this->m_value);
+ throw bad_optional_access();
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \exclude
+ 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`
+ /// \group value_or
+ 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));
+ }
+
+ /// \group value_or
+ 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() ? **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
+
+/// \group relop
+/// \brief Compares two optional objects
+/// \details If both optionals contain a value, they are compared with `T`s
+/// relational operators. Otherwise `lhs` and `rhs` are equal only if they are
+/// both empty, and `lhs` is less than `rhs` only if `rhs` is empty and `lhs`
+/// is not.
+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);
+}
+/// \group relop
+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);
+}
+/// \group relop
+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);
+}
+/// \group relop
+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);
+}
+/// \group relop
+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);
+}
+/// \group relop
+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);
+}
+
+/// \group relop_nullopt
+/// \brief Compares an optional to a `nullopt`
+/// \details Equivalent to comparing the optional to an empty optional
+template <class T>
+inline constexpr bool operator==(const optional<T> &lhs, nullopt_t) noexcept {
+ return !lhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator==(nullopt_t, const optional<T> &rhs) noexcept {
+ return !rhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator!=(const optional<T> &lhs, nullopt_t) noexcept {
+ return lhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator!=(nullopt_t, const optional<T> &rhs) noexcept {
+ return rhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator<(const optional<T> &, nullopt_t) noexcept {
+ return false;
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator<(nullopt_t, const optional<T> &rhs) noexcept {
+ return rhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator<=(const optional<T> &lhs, nullopt_t) noexcept {
+ return !lhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator<=(nullopt_t, const optional<T> &) noexcept {
+ return true;
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator>(const optional<T> &lhs, nullopt_t) noexcept {
+ return lhs.has_value();
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator>(nullopt_t, const optional<T> &) noexcept {
+ return false;
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator>=(const optional<T> &, nullopt_t) noexcept {
+ return true;
+}
+/// \group relop_nullopt
+template <class T>
+inline constexpr bool operator>=(nullopt_t, const optional<T> &rhs) noexcept {
+ return !rhs.has_value();
+}
+
+/// \group relop_t
+/// \brief Compares the optional with a value.
+/// \details If the optional has a value, it is compared with the other value
+/// using `T`s relational operators. Otherwise, the optional is considered
+/// less than the value.
+template <class T, class U>
+inline constexpr bool operator==(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs == rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator==(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs == *rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator!=(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs != rhs : true;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator!=(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs != *rhs : true;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator<(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs < rhs : true;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator<(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs < *rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator<=(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs <= rhs : true;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator<=(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs <= *rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator>(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs > rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator>(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs > *rhs : true;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator>=(const optional<T> &lhs, const U &rhs) {
+ return lhs.has_value() ? *lhs >= rhs : false;
+}
+/// \group relop_t
+template <class T, class U>
+inline constexpr bool operator>=(const U &lhs, const optional<T> &rhs) {
+ return rhs.has_value() ? lhs >= *rhs : true;
+}
+
+/// \synopsis template <class T>\nvoid swap(optional<T> &lhs, optional<T> &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);
+}
+
+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.
+///
+/// *Examples*:
+///
+/// ```
+/// int i = 42;
+/// tl::optional<int&> o = i;
+/// *o == 42; //true
+/// i = 12;
+/// *o = 12; //true
+/// &*o == &i; //true
+/// ```
+///
+/// Assignment has rebind semantics rather than assign-through semantics:
+///
+/// ```
+/// int j = 8;
+/// o = j;
+///
+/// &*o == &j; //true
+/// ```
+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)
+ /// \group and_then
+ /// Carries out some operation which returns an optional on the stored
+ /// object if there is one. \requires `std::invoke(std::forward<F>(f),
+ /// value())` returns a `std::optional<U>` for some `U`. \returns Let `U` be
+ /// the result of `std::invoke(std::forward<F>(f), value())`. Returns a
+ /// `std::optional<U>`. The return value is empty if `*this` is empty,
+ /// otherwise the return value of `std::invoke(std::forward<F>(f), value())`
+ /// is returned.
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
+ 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
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
+ 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
+ /// \group and_then
+ /// Carries out some operation which returns an optional on the stored
+ /// object if there is one. \requires `std::invoke(std::forward<F>(f),
+ /// value())` returns a `std::optional<U>` for some `U`. \returns Let `U` be
+ /// the result of `std::invoke(std::forward<F>(f), value())`. Returns a
+ /// `std::optional<U>`. The return value is empty if `*this` is empty,
+ /// otherwise the return value of `std::invoke(std::forward<F>(f), value())`
+ /// is returned.
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
+ 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);
+ }
+
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
+ 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
+ /// \group and_then
+ /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
+ 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);
+ }
+#endif
+#endif
+
+#if defined(TL_OPTIONAL_CXX14) && !defined(TL_OPTIONAL_GCC49) && \
+ !defined(TL_OPTIONAL_GCC54) && !defined(TL_OPTIONAL_GCC55)
+ /// \brief Carries out some operation on the stored object if there is one.
+ /// \returns Let `U` be the result of `std::invoke(std::forward<F>(f),
+ /// value())`. Returns a `std::optional<U>`. The return value is empty if
+ /// `*this` is empty, otherwise an `optional<U>` is constructed from the
+ /// return value of `std::invoke(std::forward<F>(f), value())` and is
+ /// returned.
+ ///
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) &;
+ template <class F> TL_OPTIONAL_11_CONSTEXPR auto map(F &&f) & {
+ return detail::optional_map_impl(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(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));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) const&;
+ template <class F> constexpr auto map(F &&f) const & {
+ return detail::optional_map_impl(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> constexpr auto map(F &&f) const&&;
+ template <class F> constexpr auto map(F &&f) const && {
+ return detail::optional_map_impl(std::move(*this), std::forward<F>(f));
+ }
+#else
+ /// \brief Carries out some operation on the stored object if there is one.
+ /// \returns Let `U` be the result of `std::invoke(std::forward<F>(f),
+ /// value())`. Returns a `std::optional<U>`. The return value is empty if
+ /// `*this` is empty, otherwise an `optional<U>` is constructed from the
+ /// return value of `std::invoke(std::forward<F>(f), value())` and is
+ /// returned.
+ ///
+ /// \group map
+ /// \synopsis template <class F> auto map(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(*this, std::forward<F>(f));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> auto map(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));
+ }
+
+ /// \group map
+ /// \synopsis template <class F> auto map(F &&f) const&;
+ 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
+ /// \group map
+ /// \synopsis template <class F> auto map(F &&f) const&&;
+ 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
+
+ /// \brief Calls `f` if the optional is empty
+ /// \requires `std::invoke_result_t<F>` must be void or convertible to
+ /// `optional<T>`. \effects If `*this` has a value, returns `*this`.
+ /// Otherwise, if `f` returns `void`, calls `std::forward<F>(f)` and returns
+ /// `std::nullopt`. Otherwise, returns `std::forward<F>(f)()`.
+ ///
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (F &&f) &;
+ 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;
+ }
+
+ /// \exclude
+ 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)();
+ }
+
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (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;
+ }
+
+ /// \exclude
+ 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)();
+ }
+
+ /// \group or_else
+ /// \synopsis template <class F> optional<T> or_else (F &&f) const &;
+ 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;
+ }
+
+ /// \exclude
+ 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
+ /// \exclude
+ 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;
+ }
+
+ /// \exclude
+ 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
+
+ /// \brief Maps the stored value with `f` if there is one, otherwise returns
+ /// `u`.
+ ///
+ /// \details If there is a value stored, then `f` is called with `**this`
+ /// and the value is returned. Otherwise `u` is returned.
+ ///
+ /// \group map_or
+ 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);
+ }
+
+ /// \group map_or
+ 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);
+ }
+
+ /// \group map_or
+ 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
+ /// \group map_or
+ 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
+
+ /// \brief Maps the stored value with `f` if there is one, otherwise calls
+ /// `u` and returns the result.
+ ///
+ /// \details If there is a value stored, then `f` is
+ /// called with `**this` and the value is returned. Otherwise
+ /// `std::forward<U>(u)()` is returned.
+ ///
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, 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), **this)
+ : std::forward<U>(u)();
+ }
+
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, 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)();
+ }
+
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, U &&u)
+ /// const &;
+ 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
+ /// \group map_or_else
+ /// \synopsis template <class F, class U>\nauto map_or_else(F &&f, U &&u)
+ /// const &&;
+ 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.
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) & {
+ return has_value() ? *this : rhs;
+ }
+
+ /// \group disjunction
+ constexpr optional disjunction(const optional &rhs) const & {
+ return has_value() ? *this : rhs;
+ }
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(const optional &rhs) && {
+ return has_value() ? std::move(*this) : rhs;
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group disjunction
+ constexpr optional disjunction(const optional &rhs) const && {
+ return has_value() ? std::move(*this) : rhs;
+ }
+#endif
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) & {
+ return has_value() ? *this : std::move(rhs);
+ }
+
+ /// \group disjunction
+ constexpr optional disjunction(optional &&rhs) const & {
+ return has_value() ? *this : std::move(rhs);
+ }
+
+ /// \group disjunction
+ TL_OPTIONAL_11_CONSTEXPR optional disjunction(optional &&rhs) && {
+ return has_value() ? std::move(*this) : std::move(rhs);
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group disjunction
+ 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
+ /// \group take
+ optional take() & {
+ optional ret = *this;
+ reset();
+ return ret;
+ }
+
+ /// \group take
+ optional take() const & {
+ optional ret = *this;
+ reset();
+ return ret;
+ }
+
+ /// \group take
+ optional take() && {
+ optional ret = std::move(*this);
+ reset();
+ return ret;
+ }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+ /// \group take
+ optional take() const && {
+ optional ret = std::move(*this);
+ reset();
+ return ret;
+ }
+#endif
+
+ using value_type = T &;
+
+ /// Constructs an optional that does not contain a value.
+ /// \group ctor_empty
+ constexpr optional() noexcept : m_value(nullptr) {}
+
+ /// \group ctor_empty
+ 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`.
+ /// \synopsis template <class U=T> constexpr optional(U &&u);
+ template <class U = T,
+ detail::enable_if_t<!detail::is_optional<detail::decay_t<U>>::value>
+ * = nullptr>
+ constexpr optional(U &&u) : m_value(std::addressof(u)) {
+ static_assert(std::is_lvalue_reference<U>::value, "U must be an lvalue");
+ }
+
+ /// \exclude
+ template <class U>
+ constexpr explicit optional(const optional<U> &rhs) : 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`.
+ ///
+ /// \requires `U` must be an lvalue reference.
+ /// \synopsis optional &operator=(U &&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) {
+ m_value = std::addressof(rhs.value());
+ return *this;
+ }
+
+ /// Constructs the value in-place, destroying the current one if there is
+ /// one.
+ ///
+ /// \group emplace
+ template <class... Args> T &emplace(Args &&... args) noexcept {
+ static_assert(std::is_constructible<T, Args &&...>::value,
+ "T must be constructible with Args");
+
+ *this = nullopt;
+ this->construct(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::swap(m_value, rhs.m_value); }
+
+ /// \returns a pointer to the stored value
+ /// \requires a value is stored
+ /// \group pointer
+ /// \synopsis constexpr const T *operator->() const;
+ constexpr const T *operator->() const { return m_value; }
+
+ /// \group pointer
+ /// \synopsis constexpr T *operator->();
+ TL_OPTIONAL_11_CONSTEXPR T *operator->() { return m_value; }
+
+ /// \returns the stored value
+ /// \requires a value is stored
+ /// \group deref
+ /// \synopsis constexpr T &operator*();
+ TL_OPTIONAL_11_CONSTEXPR T &operator*() { return *m_value; }
+
+ /// \group deref
+ /// \synopsis constexpr const T &operator*() const;
+ constexpr const T &operator*() const { return *m_value; }
+
+ /// \returns whether or not the optional has a value
+ /// \group has_value
+ constexpr bool has_value() const noexcept { return m_value != nullptr; }
+
+ /// \group has_value
+ constexpr explicit operator bool() const noexcept {
+ return m_value != nullptr;
+ }
+
+ /// \returns the contained value if there is one, otherwise throws
+ /// [bad_optional_access]
+ /// \group value
+ /// synopsis constexpr T &value();
+ TL_OPTIONAL_11_CONSTEXPR T &value() {
+ if (has_value())
+ return *m_value;
+ throw bad_optional_access();
+ }
+ /// \group value
+ /// \synopsis constexpr const T &value() const;
+ 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`
+ /// \group value_or
+ 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));
+ }
+
+ /// \group value_or
+ 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() ? **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);
+ }
+};
+} // namespace std
+
+#endif