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Simon Brand
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expected.hpp
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431
expected.hpp
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///
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// expected - An implementation of std::expected with extensions
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// Written in 2017 by Simon Brand (@TartanLlama)
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//
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// To the extent possible under law, the author(s) have dedicated all
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// copyright and related and neighboring rights to this software to the
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// public domain worldwide. This software is distributed without any warranty.
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//
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// You should have received a copy of the CC0 Public Domain Dedication
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// along with this software. If not, see
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// <http://creativecommons.org/publicdomain/zero/1.0/>.
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///
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#ifndef TL_EXPECTED_HPP
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#define TL_EXPECTED_HPP
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#include <type_traits>
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namespace tl {
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template <class E>
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class unexpected {
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public:
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static_assert(!std::is_same<E, void>, "E must not be void");
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unexpected() = delete;
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constexpr explicit unexpected(const E& e)
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: m_val(e) {}
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constexpr explicit unexpected(E&&)
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: m_val(std::move(e)) {}
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constexpr const E& value() const & { return m_val; }
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constexpr E& value() & { return m_val; }
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constexpr E&& value() && { return std::move(m_val); }
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constexpr E const&& value() const&& { return std::move(m_val); }
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private:
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E m_val; // exposition only
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};
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template <class E>
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constexpr bool
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operator==(const unexpected<E>& lhs, const unexpected<E>& rhs) {
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return lhs.value() == rhs.value();
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}
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template <class E>
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constexpr bool
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operator!=(const unexpected<E>& lhs, const unexpected<E>& rhs) {
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return lhs.value() != rhs.value();
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}
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}
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namespace detail {
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template <class T, class E, bool = std::is_trivially_destrictible<T>::value, bool = std::is_trivially_destrictible<E>::value>
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struct expected_storage_base {
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~expected_storage_base() {
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if (m_has_val) {
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m_val.~T();
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}
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else {
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m_unexpect.~unexpected<E>();
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}
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}
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bool m_has_val;
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union {
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T m_val;
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unexpected<E> m_unexpect;
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};
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};
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template <class T, class E>
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struct expected_storage_base<T,E,true,true> {
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~expected_storage_base() = default;
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bool m_has_val;
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union {
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T m_val;
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unexpected<E> m_unexpect;
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};
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};
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template <class T, class E>
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struct expected_storage_base<T,E,true,false> {
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~expected_storage_base() {
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if (!m_has_val) {
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m_unexpect.~unexpected<E>();
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}
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}
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bool m_has_val;
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union {
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T m_val;
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unexpected<E> m_unexpect;
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};
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};
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template <class T, class E>
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struct expected_storage_base<T,E,false,true> {
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~expected_storage_base() {
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if (m_has_val) {
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m_val.~T();
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}
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}
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bool m_has_val;
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union {
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T m_val;
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unexpected<U> m_unexpect;
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};
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};
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template <class T, class E>
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struct expected_storage_base<void,E,false,true> {
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~expected_storage_base() = default;
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bool m_has_val;
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struct dummy{};
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union {
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dummy m_val;
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unexpected<U> m_unexpect;
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};
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};
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template <class T, class E>
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struct expected_storage_base<void,E,false,false> {
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~expected_storage_base() {
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if (m_has_val) {
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m_val.~T();
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}
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}
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bool m_has_val;
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struct dummy{};
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union {
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dummy m_val;
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unexpected<U> m_unexpect;
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};
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};
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//TODO, conditionally delete things
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template <class T, class E>
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class expected_ctor_base{};
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}
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template <class T, class E>
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class expected : private expected_storage_base<T,E>, private expected_ctor_base<T,E> {
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static_assert(!std::is_reference<T>::value, "T must not be a reference");
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static_assert(!std::is_same<T, std::remove_cv<in_place_t>>::value, "T must not be in_place_t");
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static_assert(!std::is_same<T, std::remove_cv<unexpect_t>>::value, "T must not be unexpect_t");
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static_assert(!std::is_same<T, std::remove_cv<unexpected<E>>::value, "T must not be unexpected<E>");
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static_assert(!std::is_reference<E>::value, "E must not be a reference");
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static_assert(!std::is_same<T, void>::value, "T must not be void");
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public:
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typedef T value_type;
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typedef E error_type;
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typedef unexpected<E> unexpected_type;
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template <class U>
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struct rebind {
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using type = expected<U, error_type>;
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};
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// X.Z.4.1, constructors
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constexpr expected_storage_base() :
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m_val(T{}), m_has_val(true) {}
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template <class... Args, detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
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constexpr expected_storage_base(in_place_t, Args&&... args) :
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m_val(std::forward<Args>(args)...), m_has_val(true) {}
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template <class U, class... Args, detail::enable_if_t<std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>
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constexpr expected_storage_base(in_place_t, std::initializer_list<U> il, Args&&... args) :
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m_val(il, std::forward<Args>(args)...), m_has_val(true) {}
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template <class G = E, detail::enable_if_t<std::is_constructible<E, const G&>::value>* = nullptr, detail::enable_if_t<!std::is_convertible<const G&, E>::value>* = nullptr>
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explicit constexpr expected(unexpected<G> const& e)
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: m_unexpect(std::move(e)), m_has_value(false) {}
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template <class G = E, detail::enable_if_t<std::is_constructible<E, const G&>::value>* = nullptr, detail::enable_if_t<std::is_convertible<const G&, E>::value>* = nullptr>
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constexpr expected(unexpected<G> const& e)
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: m_unexpect(std::move(e)), m_has_value(false) {}
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template <class G = E, detail::enable_if_t<std::is_constructible<E, G&&>::value>* = nullptr, detail::enable_if_t<!std::is_convertible<G&&, E>::value>* = nullptr>
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explicit constexpr expected(unexpected<G> && e) noexcept(std::is_nothrow_constructible<E, G&&>::value)
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: m_unexpect(std::move(e)), m_has_value(false) {}
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template <class G = E, detail::enable_if_t<std::is_constructible<E, G&&>::value>* = nullptr, detail::enable_if_t<std::is_convertible<G&&, E>::value>* = nullptr>
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constexpr expected(unexpected<G> && e) noexcept(std::is_nothrow_constructible<E, G&&>::value)
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: m_unexpect(std::move(e)), m_has_value(false) {}
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template <class... Args, detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
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constexpr explicit expected(unexpect_t, Args&&... args) :
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m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
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template <class U, class... Args, detail::enable_if_t<std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
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constexpr explicit expected(unexpect_t, std::initializer_list<U> il, Args&&... args) :
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m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
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constexpr expected(const expected& rhs) {
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if (rhs.has_value()) {
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new (std::addressof(m_value)) (*rhs);
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}
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else {
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new (std::addressof(m_unexpect)) (unexpected(rhs.error()));
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}
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}
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//TODO SFINAE
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constexpr expected(expected&&) noexcept(std::is_nothrow_move_constructible_v<T> && std::is_nothrow_move_constructible_v<E>) {
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if (rhs.has_value()) {
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new (std::addressof(m_value)) (std::move(*rhs));
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}
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else {
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new (std::addressof(m_unexpect)) (unexpected(std::move(rhs.error())));
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}
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}
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//TODO SFINAE
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template <class U, class G, detail::enable_if_t<!std::is_convertible<U const&, T> || !std::is_convertible<G const&, E>::value>* = nullptr>
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explicit constexpr expected(const expected<U, G>& rhs) {
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if (rhs.has_value()) {
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new (std::addressof(m_value)) (*rhs);
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}
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else {
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new (std::addressof(m_unexpect)) (unexpected(rhs.error()));
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}
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}
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//TODO SFINAE
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template <class U, class G, detail::enable_if_t<!std::is_convertible<U&&, T> || !std::is_convertible<G&&, E>::value>* = nullptr>
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explicit constexpr expected(const expected<U, G>& rhs) {
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if (rhs.has_value()) {
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new (std::addressof(m_value)) (*rhs);
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}
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else {
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new (std::addressof(m_unexpect)) (unexpected(rhs.error()));
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}
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}
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//TODO SFINAE
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template <class U, class G, detail::enable_if_t<std::is_convertible<U&&, T> || std::is_convertible<G&&, E>::value>* = nullptr>
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constexpr expected(expected<U, G>&&) {
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if (rhs.has_value()) {
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new (std::addressof(m_value)) (std::move(*rhs));
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}
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else {
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new (std::addressof(m_unexpect)) (unexpected(std::move(rhs.error())));
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}
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}
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//TODO SFINAE
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template <class U = T, detail::enable_if_t<!std::is_convertible<U&&, T>::value>* = nullptr>
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explicit constexpr expected(U&& v)
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: expected_storage_base(in_place, std::forward<U>(v))
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{}
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//TODO SFINAE
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template <class U = T, detail::enable_if_t<std::is_convertible<U&&, T>::value>* = nullptr>
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constexpr expected(U&& v)
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: expected_storage_base(in_place, std::forward<U>(v))
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{}
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//TODO
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expected& operator=(const expected&);
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expected& operator=(expected&&) noexcept(see below);
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template <class U = T> expected& operator=(U&&);
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template <class G = E>
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expected& operator=(const unexpected<G>&);
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template <class G = E>
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expected& operator=(unexpected<G>&&) noexcept(see below);
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template <class... Args>
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void emplace(Args&&...);
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template <class U, class... Args>
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void emplace(initializer_list<U>, Args&&...);
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//TODO SFINAE
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void swap(expected& rhs) noexcept(std::is_nothrow_move_constructible<T>::value && noexcept(swap(declval<T&>(), declval<T&>())) && std::is_nothrow_move_constructible<E>::value && noexcept(swap(declval<E&>(), declval<E&>())))
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{
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if (has_value() && rhs.has_value()) {
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using std::swap;
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swap(m_val, rhs.m_val);
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}
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else if (!has_value() && rhs.has_value()) {
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using std::swap;
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swap(m_unexpect, rhs.m_unexpect);
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}
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else if (has_value()) {
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auto temp = std::move(rhs.m_unexpect);
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new (std::addressof(rhs.m_val)) (m_val);
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new (std::addressof(m_unexpect)) (temp);
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std::swap(m_has_value, rhs.m_has_value);
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}
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else {
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auto temp = std::move(m_unexpect);
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new (std::addressof(m_val)) (rhs.m_val);
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new (std::addressof(rhs.m_unexpect)) (temp);
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std::swap(m_has_value, rhs.m_has_value);
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}
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}
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constexpr const T* operator ->() const { return std::addressof(m_val); }
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constexpr T* operator ->() { return std::addressof(m_val); }
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constexpr const T& operator *() const& { return m_val; }
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constexpr T& operator *() & { return m_val; }
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constexpr const T&& operator *() const && { return std::move(m_val); }
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constexpr T&& operator *() && { return std::move(m_val); }
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constexpr explicit operator bool() const noexcept { return m_has_val; }
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constexpr bool has_value() const noexcept { return m_has_val; }
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constexpr const T& value() const& {
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if (!m_has_value) throw bad_expected_access();
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return m_value;
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}
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constexpr T& value() & {
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if (!m_has_value) throw bad_expected_access();
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return m_value;
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}
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constexpr const T&& value() const && {
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if (!m_has_value) throw bad_expected_access();
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return std::move(m_value);
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}
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constexpr T&& value() && {
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if (!m_has_value) throw bad_expected_access();
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return std::move(m_value);
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}
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constexpr const E& error() const& { return m_unexpect.value(); }
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constexpr E& error() & { return m_unexpect.value(); }
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constexpr const E&& error() const && { return std:move(m_unexpect.value()); }
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constexpr E&& error() && { return std:move(m_unexpect.value()); }
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template <class U>
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constexpr T value_or(U&& v) const& {
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static_assert(std::is_copy_constructible<T>::value && std::is_convertible<U&&, T>::value, "T must be copy-constructible and convertible to from U&&");
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return bool(*this) ? **this : static_cast<T>(std::forward<U>(v));
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}
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template <class U>
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T value_or(U&&) && {
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static_assert(std::is_move_constructible<T>::value && std::is_convertible<U&&, T>::value, "T must be move-constructible and convertible to from U&&");
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return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));
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}
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};
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//TODO
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template <class E>
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class expected<void, E> {
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};
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struct unexpect_t {
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unexpect_t() = default;
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};
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inline constexpr unexpect_t unexpect{};
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template <class E>
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class bad_expected_access : public bad_expected_access<void> {
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public:
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explicit bad_expected_access(E e)
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: m_val(std::move(e)) {}
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virtual const char* what() const noexcept override {
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return "Bad expected access";
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}
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const E& error() const& { return m_val; }
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E& error() & { return m_val; }
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const E&& error() const && { return std::move(m_val); }
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E&& error() && { return std::move(m_val); }
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private:
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E m_val;
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};
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template <>
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class bad_expected_access<void> : public exception {
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public:
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explicit bad_expected_access();
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};
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template <>
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class bad_expected_access<void>;
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template <class T, class E>
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constexpr bool operator==(const expected<T, E>& lhs, const expected<T, E>& rhs) {
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return (lhs.has_value() != rhs.has_value()) ? false :
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(!lhs.has_value() ? lhs.error() == rhs.error()
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: *lhs == *rhs);
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}
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template <class T, class E>
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constexpr bool operator!=(const expected<T, E>& lhs, const expected<T, E>& rhs) {
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return (lhs.has_value() != rhs.has_value()) ? true :
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(!lhs.has_value() ? lhs.error() != rhs.error()
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: *lhs != *rhs);
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}
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template <class T, class E>
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constexpr bool operator==(const expected<T, E>& x, const T& v) {
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return x.has_value() ? *x == v : false;
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}
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template <class T, class E>
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constexpr bool operator==(const T& v, const expected<T, E>& x) {
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return x.has_value() ? *x == v : false;
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}
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template <class T, class E>
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constexpr bool operator!=(const expected<T, E>& x, const T& v) {
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return x.has_value() ? *x != v : true;
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}
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template <class T, class E>
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constexpr bool operator!=(const T& v, const expected<T, E>& x) {
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return x.has_value() ? *x != v : true;
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}
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template <class T, class E>
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constexpr bool operator==(const expected<T, E>& x, const unexpected<E>& e) {
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return x.has_value() ? true : x.error() == e.value();
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}
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template <class T, class E>
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||||
constexpr bool operator==(const unexpected<E>& e, const expected<T, E>& x) {
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||||
return x.has_value() ? true : x.error() == e.value();
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||||
}
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||||
template <class T, class E>
|
||||
constexpr bool operator!=(const expected<T, E>& x, const unexpected<E>& e) {
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||||
return x.has_value() ? false : x.error() != e.value();
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||||
}
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||||
template <class T, class E>
|
||||
constexpr bool operator!=(const unexpected<E>& e, const expected<T, E>& x) {
|
||||
return x.has_value() ? false : x.error() != e.value();
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||||
}
|
||||
|
||||
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||||
//TODO is_swappable
|
||||
template <class T, class E, detail::enable_if_t<std::is_move_constructible<T>::value && std::is_move_constructible<E>::value>* = nullptr>
|
||||
void swap(expected<T, E>& lhs, expected<T, E>& rhs) noexcept(noexcept(lhs.swap(rhs))) {
|
||||
lhs.swap(rhs);
|
||||
}
|
||||
|
||||
#endif
|
||||
Reference in New Issue
Block a user