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258 lines
9.7 KiB
258 lines
9.7 KiB
#pragma once
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namespace exopt::types {
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#if 0
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//XXX: Eh, this trait design is NOT GOOD. Figure out a better one
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namespace traits {
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template<typename T>
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struct impl_clone {
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typedef T type;
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constexpr static T clone(T const& v) const noexcept(std::is_nothrow_copy_constructible_v<type>) { return v; }
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};
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template<>
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struct impl_clone<void> {};
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template<typename> struct clone;
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template<>
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struct clone : impl_clone<void> {};
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template<typename T>
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struct clone : impl_clone<std::conditional_t< std::is_copy_constructible_v<T>, T, void> > {};
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template<typename T>
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struct clone : impl_clone<std::conditional_t
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< requires(requires(T const& self) {
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{ self.clone() } noexcept(std::is_nothrow_copy_constructible_v<T>)
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-> std::same_as<T>;
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})
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, T
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, void
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> > {
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constexpr static T clone(T const&
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};
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}
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template<typename T>
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concept Clone = requires(T const& self) {
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typename traits::clone<T>::type;
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{ traits::clone<T>::clone(self) } noexcept(std::is_nothrow_copy_constructible_v<T>) -> std::same_as<T>;
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} or requires(T const& self) {
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{ self.clone() } noexcept(std::is_nothrow_copy_constructible_v<T>) -> std::same_as<T>;
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};
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#endif
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namespace either [[gnu::visibility("internal")]] {
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//TODO: A version with std::shared_ptr<T> instead
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template<typename T>//, typename P = T*>
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class Cow {
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using var_t = std::variant<pointer_type // Borrowed
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, value_type>; // Owned
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public:
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//TODO: Use pointer traits of P to deduce `pointer_type`, so we can have P be a shared_ptr too. Or perhaps, a specialisation for `Cow<std::shared_ptr<T>>` would be better
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using value_type = std::remove_cvref_t<T>;
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constexpr static inline bool Writeable = std::is_copy_constructible_v<value_type>;
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constexpr static inline bool NTWriteable = std::is_nothrow_copy_constructible_v<value_type>;
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using reference_type = value_type &;
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using const_reference_type = value_type const&;
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using move_reference_type = value_type &&;
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using pointer_type = value_type *;
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using const_pointer_type = value_type const*;
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constexpr Cow(std::add_rvalue_reference_t<T> value) noexcept(std::is_nothrow_constructible_v<value_type, decltype(value)>)
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: m_value{std::move(value)} {}
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constexpr explicit(std::is_convertible_v<std::add_rvalue_reference<T>, pointer_type>)
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Cow(pointer_type p) noexcept
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: m_value{p} {}
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constexpr explicit Cow(std::nullptr_t) noexcept
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: Cow(std::move(static_cast<pointer_type>(nullptr))) {}
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constexpr Cow(Cow const& copy) noexcept
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: m_value(copy.get()) {}
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constexpr Cow(Cow&& move) noexcept(std::is_nothrow_move_constructible_v<value_type>)
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: m_value(std::move(move.m_value)) { move.clear(); /* XXX: Is this needed? I think it is, to ensure that Cow<T> knows if it's been moved, even though std::variant already knows */ }
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/// Return a newly copy-constructed owned object `T` from the referred (or held) value.
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constexpr Cow clone() const noexcept(std::is_nothrow_copy_constructible_v<value_type>) requires(std::is_copy_constructible_v<T>)
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{
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if(const auto* pref = this->get())
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return { *pref };
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else return { nullptr };
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}
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//TODO: Operator overloads for access to `value_type`: operator*, operator->, etc.
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constexpr Cow(Cow&& move) noexcept(std::is_nothrow_move_constructible_v<value_type>) {
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if(this != std::addressof(move)) {
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if(__builtin_expect(move.is_empty(), false)) clear();
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else {
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m_value.emplace<value_type>(std::move(move).as_ref())
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move.clear();
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}
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} return *this;
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}
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constexpr Cow(Cow const& copy) noexcept(std::is_nothrow_destructible_v<value_type>) {
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if(this != std::addressof(copy)) {
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m_value.emplace<pointer_type>(copy.get());
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} return *this;
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}
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constexpr ~Cow() noexcept(std::is_nothrow_destructible_v<value_type>) = default;
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constexpr move_reference_type as_ref() && {
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return make_owned();
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}
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constexpr reference_type as_ref() & {
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return make_owned();
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}
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constexpr const_reference_type as_ref() const {
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return std::visit([](const auto& arg) -> const_reference_type {
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using U = std::remove_cvref_t<decltype(arg)>>;
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if constexpr(std::is_same_v<U, value_type)
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return std::forward<decltype(arg)>(arg);
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else return *arg;
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}, m_value);
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}
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//TODO: ^ UNLIKELY(is_empty()) null-checks for `*arg`.
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constexpr reference_type operator*() & noexcept {
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return as_ref();
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}
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constexpr move_reference_type operator*() && noexcept {
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return as_ref();
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}
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constexpr const_reference_type operator*() const noexcept {
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return as_ref();
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}
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constexpr pointer_type operator->() noexcept {
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return get();
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}
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constexpr const_pointer_type operator->() noexcept {
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return get();
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}
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constexpr const_pointer_type get() const noexcept {
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return std::visit([](const auto& arg) -> const_pointer_type {
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using U = std::remove_cvref_t<decltype(arg)>;
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if constexpr(std::is_same_v<U, value_type>)
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return std::addressof(arg);
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else return arg;
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}, m_value);
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}
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constexpr pointer_type get() noexcept {
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return std::addressof(make_owned());
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/*
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return std::visit([](auto& arg) -> pointer_type {
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using U = std::remove_cvref_t<decltype(arg)>;
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if constexpr(std::is_same_v<U, value_type>)
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return std::addressof(arg);
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else return arg;
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}, m_value);*/
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}
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constexpr reference_type make_owned() & noexcept(NTWriteable) requires(Writeable) {
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if(const auto* ct_from = std::visit([&m_value](auto& arg) -> auto* {
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using U = std::remove_cvref_t<decltype(arg)>;
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if constexpr(std::is_same_v<U, pointer_type>) return arg;
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else return nullptr;
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//if constexpr(std::is_same_v<U, value_type>) return false;
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//else if(auto * refp = std::get_if<pointer_type>(m_value))
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}, m_value)) return m_value.emplace<value_type>(*ct_from); //XXX: Do we need to create a temporary here for creating invariants by reading the old invariant?
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}
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constexpr move_reference_type make_owned() && noexcept(NTWriteable) requires(Writeable) {
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if(const auto* ct_from = std::visit([&m_value](auto&& arg) -> auto* {
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using U = std::remove_cvref_t<decltype(arg)>;
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//TODO: I don't think this works the way I want it to... We'll need to emplace inside this function I think, since the moved temporary has been moved. It might not matter though.
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if constexpr(std::is_same_v<U, pointer_type>) return arg;
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else return nullptr;
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//if constexpr(std::is_same_v<U, value_type>) return false;
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//else if(auto * refp = std::get_if<pointer_type>(m_value))
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}, std::move(m_value))) return std::move(m_value.emplace<value_type>(*ct_from)); //XXX: Do we need to create a temporary here for creating invariants by reading the old invariant?
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}
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//These commented out visits modify the pointee of the borrowed invariant. THIS IS NOT WHAT WE WANT. Instead, we emplace a copy and then copy it again (possibly elided: &) or return it as an rvalue reference (elided: &&)
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constexpr value_type into_owned() & noexcept(NTWriteable) requires(Writeable) {
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return make_owned();
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/*return std::visit([](auto&& arg) -> move_reference_type {
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using U = std::remove_cvref_t<decltype(arg)>;
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if constexpr(std::is_same_v<U, value_type>)
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return std::move(arg);
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else return std::move(*arg);
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}, std::move(m_value));*/
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}
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constexpr move_reference_type into_owned() && noexcept(NTWriteable) requires(Writeable) {
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return make_owned();
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/*return std::move(std::visit([](auto&& arg) -> move_reference_type {
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using U = std::remove_cvref_t<decltype(arg)>;
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if constexpr(std::is_same_v<U, value_type>)
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return std::move(arg);
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else return std::move(*arg);
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}, std::move(m_value)));*/
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}
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protected:
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constexpr bool is_empty() const noexcept {
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if(const const_pointer_type* p_ref = std::get_if<pointer_type>(&m_value))
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if(!p_ref) return true;
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return false;
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}
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constexpr void clear() noexcept(std::is_nothrow_destructible_v<value_type>) {
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m_value.emplace<pointer_type>(nullptr);
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}
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private:
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var_t m_value;
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};
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//template<typename T>
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//TODO: We want it to work: class Cow<std::unique_ptr<T>> : public Cow<T> {};
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#if 0
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template<typename T>
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class Cow<std::shared_ptr<T>> {
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using var_t = std::variant<
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std::weak_ptr<value_type> // Borrowed
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, std::shared_ptr<value_type>>; // Owned
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public:
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using value_type = std::remove_cvref_t<T>;
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using reference_type = value_type &;
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using const_reference_type = value_type const&;
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using move_reference_type = value_type &&;
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using pointer_type = value_type;
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using const_pointer_type = value_type const*;
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//TODO: AutoCow: See above comment about RC'd lifetimes with shallow coppies.
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// How should we implement this... I think weak for borrowed and shared for owned is good, since we can still use shared_ptr's aliasing ctor to apply clone() (copy-construction) to the `value_type` directly while keeping the ref-count.
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// XXX: Therfore, there should never be *any* strictly-aliasing variants both exposing the same `value_type`, despite *all* the variants managing the lifetime of the `value_type`. I think... Hnm... Can we get shared_ptr<T>'s aliasing constructor to *expose* a newly constructed `value_type` while managing the new one and the old one? XXX: Should we even manage the old one at all after a `clone()`? I actually don't think we should, since `clone()` should detach lifetime from the instance that it was called since it's a newly constructed (owned) object.
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private:
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var_t m_value;
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};
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#endif
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}
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/// Manually lifetime managed Cow<T>
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using either::Cow;
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/// RC-lifetime managed Cow<T>
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template<typename T>
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using RcCow = Cow<std::shared_ptr<T>>;
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/// Boxed unique Cow<T>
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template<typename T>
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using BoxCow = Cow<std::unique_ptr<T>>;
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}
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