add octa::Maybe, representing optional values for simpler error handling
parent
10fa69dcd1
commit
9f58a6c399
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@ -176,7 +176,7 @@ template<typename T> T from_big_endian(T x) { return FromBigEndian<T>()(x); }
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/* hash */
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template<typename T> struct ToHash {
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using Argument = const T &;
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using Argument = T;
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using Result = octa::Size;
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octa::Size operator()(const T &v) const {
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@ -0,0 +1,430 @@
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/* Option type implementation. Inspired by libc++.
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*
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* This file is part of OctaSTD. See COPYING.md for futher information.
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*/
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#ifndef OCTA_MAYBE_HH
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#define OCTA_MAYBE_HH
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#include "octa/types.hh"
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#include "octa/type_traits.hh"
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#include "octa/memory.hh"
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#include "octa/utility.hh"
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#include "octa/initializer_list.hh"
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#include "octa/functional.hh"
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namespace octa {
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struct InPlace {};
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constexpr InPlace in_place = InPlace();
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struct Nothing {
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explicit constexpr Nothing(int) {}
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};
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constexpr Nothing nothing = Nothing(0);
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namespace detail {
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template<typename T, bool = octa::IsTriviallyDestructible<T>::value>
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class MaybeStorage {
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protected:
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using Value = T;
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union {
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char p_null_state;
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Value p_value;
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};
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bool p_engaged = false;
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constexpr MaybeStorage(): p_null_state('\0') {}
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MaybeStorage(const MaybeStorage &v): p_engaged(v.p_engaged) {
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if (p_engaged) ::new(octa::address_of(p_value)) Value(v.p_value);
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}
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MaybeStorage(MaybeStorage &&v): p_engaged(v.p_engaged) {
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if (p_engaged)
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::new(octa::address_of(p_value)) Value(octa::move(v.p_value));
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}
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constexpr MaybeStorage(const Value &v): p_value(v), p_engaged(true) {}
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constexpr MaybeStorage(Value &&v): p_value(octa::move(v)), p_engaged(true) {}
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template<typename ...A> constexpr MaybeStorage(octa::InPlace, A &&...args):
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p_value(octa::forward<A>(args)...), p_engaged(true) {}
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~MaybeStorage() {
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if (p_engaged) p_value.~Value();
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}
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};
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template<typename T>
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class MaybeStorage<T, true> {
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protected:
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using Value = T;
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union {
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char p_null_state;
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Value p_value;
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};
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bool p_engaged = false;
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constexpr MaybeStorage(): p_null_state('\0') {}
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MaybeStorage(const MaybeStorage &v): p_engaged(v.p_engaged) {
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if (p_engaged) ::new(octa::address_of(p_value)) Value(v.p_value);
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}
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MaybeStorage(MaybeStorage &&v): p_engaged(v.p_engaged) {
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if (p_engaged)
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::new(octa::address_of(p_value)) Value(octa::move(v.p_value));
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}
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constexpr MaybeStorage(const Value &v): p_value(v), p_engaged(true) {}
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constexpr MaybeStorage(Value &&v):
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p_value(octa::move(v)), p_engaged(true) {}
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template<typename ...A>
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constexpr MaybeStorage(octa::InPlace, A &&...args):
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p_value(octa::forward<A>(args)...), p_engaged(true) {}
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};
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}
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template<typename T>
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class Maybe: private octa::detail::MaybeStorage<T> {
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using Base = octa::detail::MaybeStorage<T>;
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public:
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using Value = T;
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static_assert(!octa::IsReference<T>::value,
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"Initialization of Maybe with a reference type is not allowed.");
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static_assert(!octa::IsSame<octa::RemoveCv<T>, octa::InPlace>::value,
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"Initialization of Maybe with InPlace is not allowed.");
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static_assert(!octa::IsSame<octa::RemoveCv<T>, octa::Nothing>::value,
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"Initialization of Maybe with Nothing is not allowed.");
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static_assert(octa::IsObject<T>::value,
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"Initialization of Maybe with non-object type is not allowed.");
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static_assert(octa::IsDestructible<T>::value,
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"Initialization of Maybe with a non-destructible object is not allowed.");
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constexpr Maybe() {}
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Maybe(const Maybe &) = default;
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Maybe(Maybe &&) = default;
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constexpr Maybe(octa::Nothing) {}
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constexpr Maybe(const Value &v): Base(v) {}
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constexpr Maybe(Value &&v): Base(octa::move(v)) {}
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template<typename ...A, typename = octa::EnableIf<
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octa::IsConstructible<T, A...>::value>>
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constexpr explicit Maybe(octa::InPlace, A &&...args): Base(octa::in_place,
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octa::forward<A>(args)...) {}
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template<typename U, typename ...A, typename = typename octa::EnableIf<
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octa::IsConstructible<T, std::initializer_list<U> &, A...>::value>>
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constexpr explicit
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Maybe(octa::InPlace, std::initializer_list<U> il, A &&...args):
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Base(octa::in_place, il, octa::forward<A>(args)...) {}
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~Maybe() = default;
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Maybe &operator=(Nothing) {
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if (this->p_engaged) {
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this->p_value.~Value();
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this->p_engaged = false;
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}
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return *this;
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}
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Maybe &operator=(const Maybe &v) {
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if (this->p_engaged == v.p_engaged) {
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if (this->p_engaged) this->p_value = v.p_value;
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} else {
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if (this->p_engaged)
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this->p_value.~Value();
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else
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::new(octa::address_of(this->p_value)) Value(v.p_value);
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this->p_engaged = v.p_engaged;
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}
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return *this;
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}
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Maybe &operator=(Maybe &&v) {
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if (this->p_engaged == v.p_engaged) {
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if (this->p_engaged) this->p_value = octa::move(v.p_value);
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} else {
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if (this->p_engaged)
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this->p_value.~Value();
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else {
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::new(octa::address_of(this->p_value))
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Value(octa::move(v.p_value));
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}
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this->p_engaged = v.p_engaged;
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}
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return *this;
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}
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template<typename U, typename = octa::EnableIf<
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octa::IsSame<octa::RemoveReference<U>, Value>::value &&
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octa::IsConstructible<Value, U>::value &&
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octa::IsAssignable<Value &, U>::value
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>>
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Maybe &operator=(U &&v) {
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if (this->p_engaged) {
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this->p_value = octa::forward<U>(v);
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} else {
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::new(octa::address_of(this->p_value)) Value(octa::forward<U>(v));
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this->p_engaged = true;
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}
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return *this;
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}
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template<typename ...A, typename = octa::EnableIf<
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octa::IsConstructible<Value, A...>::value
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>>
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void emplace(A &&...args) {
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*this = octa::nothing;
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::new(octa::address_of(this->p_value))
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Value(octa::forward<A>(args)...);
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this->p_engaged = true;
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}
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template<typename U, typename ...A, typename = octa::EnableIf<
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octa::IsConstructible<Value, std::initializer_list<U> &, A...>::value
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>>
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void emplace(std::initializer_list<U> il, A &&...args) {
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*this = octa::nothing;
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::new(octa::address_of(this->p_value))
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Value(il, octa::forward<A>(args)...);
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this->p_engaged = true;
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}
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constexpr const Value *operator->() const {
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return octa::address_of(this->p_value);
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}
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Value *operator->() {
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return octa::address_of(this->p_value);
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}
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constexpr const Value &operator*() const {
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return this->p_value;
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}
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Value &operator*() {
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return this->p_value;
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}
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constexpr explicit operator bool() const { return this->p_engaged; }
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constexpr const Value &value() const {
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return this->p_value;
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}
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Value &value() {
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return this->p_value;
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}
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template<typename U>
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constexpr Value value_or(U &&v) const & {
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static_assert(octa::IsCopyConstructible<Value>::value,
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"Maybe<T>::value_or: T must be copy constructible");
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static_assert(octa::IsConvertible<U, Value>::value,
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"Maybe<T>::value_or: U must be convertible to T");
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return this->p_engaged ? this->p_value : Value(octa::forward<U>(v));
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}
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template<typename U>
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Value value_or(U &&v) && {
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static_assert(octa::IsMoveConstructible<Value>::value,
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"Maybe<T>::value_or: T must be copy constructible");
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static_assert(octa::IsConvertible<U, Value>::value,
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"Maybe<T>::value_or: U must be convertible to T");
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return this->p_engaged ? octa::move(this->p_value)
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: Value(octa::forward<U>(v));
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}
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void swap(Maybe &v) {
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if (this->p_engaged == v.p_engaged) {
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if (this->p_engaged) octa::swap(this->p_value, v.p_value);
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} else {
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if (this->p_engaged) {
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::new(octa::address_of(v.p_value))
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Value(octa::move(this->p_value));
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this->p_value.~Value();
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} else {
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::new(octa::address_of(this->p_value))
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Value(octa::move(v.p_value));
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v.p_value.~Value();
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}
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octa::swap(this->p_engaged, v.p_engaged);
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}
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}
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octa::Size to_hash() const {
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return this->p_engaged ? octa::ToHash<T>()(this->p_value) : 0;
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}
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};
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/* maybe vs maybe */
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template<typename T>
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static inline constexpr bool operator==(const Maybe<T> &a, const Maybe<T> &b) {
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return (bool(a) != bool(b)) ? false : (!bool(a) ? true : (*a == *b));
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}
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template<typename T>
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static inline constexpr bool operator!=(const Maybe<T> &a, const Maybe<T> &b) {
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return !(a == b);
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}
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template<typename T>
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static inline constexpr bool operator<(const Maybe<T> &a, const Maybe<T> &b) {
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return !bool(b) ? false : (!bool(a) ? true : (*a < *b));
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}
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template<typename T>
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static inline constexpr bool operator>(const Maybe<T> &a, const Maybe<T> &b) {
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return b < a;
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}
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template<typename T>
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static inline constexpr bool operator<=(const Maybe<T> &a, const Maybe<T> &b) {
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return !(b < a);
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}
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template<typename T>
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static inline constexpr bool operator>=(const Maybe<T> &a, const Maybe<T> &b) {
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return !(a < b);
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}
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/* maybe vs nothing */
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template<typename T>
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static inline constexpr bool operator==(const Maybe<T> &v, Nothing) {
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return !bool(v);
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}
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template<typename T>
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static inline constexpr bool operator==(Nothing, const Maybe<T> &v) {
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return !bool(v);
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}
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template<typename T>
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static inline constexpr bool operator!=(const Maybe<T> &v, Nothing) {
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return bool(v);
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}
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template<typename T>
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static inline constexpr bool operator!=(Nothing, const Maybe<T> &v) {
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return bool(v);
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}
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template<typename T>
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static inline constexpr bool operator<(const Maybe<T> &, Nothing) {
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return false;
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}
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template<typename T>
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static inline constexpr bool operator<(Nothing, const Maybe<T> &v) {
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return bool(v);
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}
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template<typename T>
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static inline constexpr bool operator<=(const Maybe<T> &v, Nothing) {
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return !bool(v);
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}
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template<typename T>
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static inline constexpr bool operator<=(Nothing, const Maybe<T> &) {
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return true;
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}
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template<typename T>
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static inline constexpr bool operator>(const Maybe<T> &v, Nothing) {
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return bool(v);
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}
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template<typename T>
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static inline constexpr bool operator>(Nothing, const Maybe<T> &) {
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return false;
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}
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template<typename T>
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static inline constexpr bool operator>=(const Maybe<T> &, Nothing) {
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return true;
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}
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template<typename T>
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static inline constexpr bool operator>=(Nothing, const Maybe<T> &v) {
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return !bool(v);
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}
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/* maybe vs T */
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template<typename T>
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static inline constexpr bool operator==(const Maybe<T> &a, const T &b) {
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return bool(a) ? (*a == b) : false;
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}
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template<typename T>
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static inline constexpr bool operator==(const T &b, const Maybe<T> &a) {
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return bool(a) ? (*a == b) : false;
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}
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template<typename T>
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static inline constexpr bool operator!=(const Maybe<T> &a, const T &b) {
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return bool(a) ? !(*a == b) : true;
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}
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template<typename T>
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static inline constexpr bool operator!=(const T &b, const Maybe<T> &a) {
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return bool(a) ? !(*a == b) : true;
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}
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template<typename T>
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static inline constexpr bool operator<(const Maybe<T> &a, const T &b) {
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return bool(a) ? octa::Less<T>()(*a, b) : true;
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}
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template<typename T>
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static inline constexpr bool operator<(const T &b, const Maybe<T> &a) {
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return bool(a) ? octa::Less<T>()(b, *a) : false;
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}
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template<typename T>
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static inline constexpr bool operator<=(const Maybe<T> &a, const T &b) {
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return !(a > b);
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}
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template<typename T>
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static inline constexpr bool operator<=(const T &b, const Maybe<T> &a) {
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return !(b > a);
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}
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template<typename T>
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static inline constexpr bool operator>(const Maybe<T> &a, const T &b) {
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return bool(a) ? (b < a) : true;
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}
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template<typename T>
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static inline constexpr bool operator>(const T &b, const Maybe<T> &a) {
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return bool(a) ? (a < b) : true;
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}
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template<typename T>
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static inline constexpr bool operator>=(const Maybe<T> &a, const T &b) {
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return !(a < b);
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}
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template<typename T>
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static inline constexpr bool operator>=(const T &b, const Maybe<T> &a) {
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return !(b < a);
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}
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/* make maybe */
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template<typename T>
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constexpr Maybe<octa::Decay<T>> make_maybe(T &&v) {
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return Maybe<octa::Decay<T>>(octa::forward<T>(v));
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}
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} /* namespace octa */
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#endif
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