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353 lines
14 KiB
353 lines
14 KiB
#ifndef AL_OPTIONAL_H
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#define AL_OPTIONAL_H
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#include <initializer_list>
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#include <type_traits>
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#include <utility>
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#include "almalloc.h"
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namespace al {
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struct nullopt_t { };
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struct in_place_t { };
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constexpr nullopt_t nullopt{};
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constexpr in_place_t in_place{};
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#define NOEXCEPT_AS(...) noexcept(noexcept(__VA_ARGS__))
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namespace detail_ {
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/* Base storage struct for an optional. Defines a trivial destructor, for types
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* that can be trivially destructed.
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*/
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template<typename T, bool = std::is_trivially_destructible<T>::value>
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struct optstore_base {
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bool mHasValue{false};
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union {
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char mDummy{};
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T mValue;
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};
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constexpr optstore_base() noexcept { }
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template<typename ...Args>
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constexpr explicit optstore_base(in_place_t, Args&& ...args)
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noexcept(std::is_nothrow_constructible<T, Args...>::value)
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: mHasValue{true}, mValue{std::forward<Args>(args)...}
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{ }
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~optstore_base() = default;
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};
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/* Specialization needing a non-trivial destructor. */
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template<typename T>
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struct optstore_base<T, false> {
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bool mHasValue{false};
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union {
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char mDummy{};
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T mValue;
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};
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constexpr optstore_base() noexcept { }
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template<typename ...Args>
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constexpr explicit optstore_base(in_place_t, Args&& ...args)
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noexcept(std::is_nothrow_constructible<T, Args...>::value)
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: mHasValue{true}, mValue{std::forward<Args>(args)...}
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{ }
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~optstore_base() { if(mHasValue) al::destroy_at(std::addressof(mValue)); }
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};
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/* Next level of storage, which defines helpers to construct and destruct the
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* stored object.
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*/
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template<typename T>
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struct optstore_helper : public optstore_base<T> {
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using optstore_base<T>::optstore_base;
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template<typename... Args>
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constexpr void construct(Args&& ...args) noexcept(std::is_nothrow_constructible<T, Args...>::value)
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{
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al::construct_at(std::addressof(this->mValue), std::forward<Args>(args)...);
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this->mHasValue = true;
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}
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constexpr void reset() noexcept
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{
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if(this->mHasValue)
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al::destroy_at(std::addressof(this->mValue));
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this->mHasValue = false;
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}
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constexpr void assign(const optstore_helper &rhs)
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noexcept(std::is_nothrow_copy_constructible<T>::value
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&& std::is_nothrow_copy_assignable<T>::value)
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{
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if(!rhs.mHasValue)
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this->reset();
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else if(this->mHasValue)
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this->mValue = rhs.mValue;
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else
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this->construct(rhs.mValue);
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}
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constexpr void assign(optstore_helper&& rhs)
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noexcept(std::is_nothrow_move_constructible<T>::value
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&& std::is_nothrow_move_assignable<T>::value)
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{
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if(!rhs.mHasValue)
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this->reset();
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else if(this->mHasValue)
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this->mValue = std::move(rhs.mValue);
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else
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this->construct(std::move(rhs.mValue));
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}
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};
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/* Define copy and move constructors and assignment operators, which may or may
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* not be trivial.
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*/
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template<typename T, bool trivial_copy = std::is_trivially_copy_constructible<T>::value,
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bool trivial_move = std::is_trivially_move_constructible<T>::value,
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/* Trivial assignment is dependent on trivial construction+destruction. */
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bool = trivial_copy && std::is_trivially_copy_assignable<T>::value
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&& std::is_trivially_destructible<T>::value,
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bool = trivial_move && std::is_trivially_move_assignable<T>::value
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&& std::is_trivially_destructible<T>::value>
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struct optional_storage;
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/* Some versions of GCC have issues with 'this' in the following noexcept(...)
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* statements, so this macro is a workaround.
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*/
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#define _this std::declval<optional_storage*>()
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/* Completely trivial. */
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template<typename T>
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struct optional_storage<T, true, true, true, true> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage&) = default;
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constexpr optional_storage& operator=(optional_storage&&) = default;
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};
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/* Non-trivial move assignment. */
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template<typename T>
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struct optional_storage<T, true, true, true, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage&) = default;
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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/* Non-trivial move construction. */
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template<typename T>
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struct optional_storage<T, true, false, true, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&& rhs) NOEXCEPT_AS(_this->construct(std::move(rhs.mValue)))
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{ if(rhs.mHasValue) this->construct(std::move(rhs.mValue)); }
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constexpr optional_storage& operator=(const optional_storage&) = default;
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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/* Non-trivial copy assignment. */
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template<typename T>
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struct optional_storage<T, true, true, false, true> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&&) = default;
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};
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/* Non-trivial copy construction. */
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template<typename T>
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struct optional_storage<T, false, true, false, true> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage &rhs) NOEXCEPT_AS(_this->construct(rhs.mValue))
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{ if(rhs.mHasValue) this->construct(rhs.mValue); }
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&&) = default;
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};
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/* Non-trivial assignment. */
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template<typename T>
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struct optional_storage<T, true, true, false, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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/* Non-trivial assignment, non-trivial move construction. */
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template<typename T>
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struct optional_storage<T, true, false, false, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage&) = default;
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constexpr optional_storage(optional_storage&& rhs) NOEXCEPT_AS(_this->construct(std::move(rhs.mValue)))
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{ if(rhs.mHasValue) this->construct(std::move(rhs.mValue)); }
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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/* Non-trivial assignment, non-trivial copy construction. */
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template<typename T>
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struct optional_storage<T, false, true, false, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage &rhs) NOEXCEPT_AS(_this->construct(rhs.mValue))
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{ if(rhs.mHasValue) this->construct(rhs.mValue); }
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constexpr optional_storage(optional_storage&&) = default;
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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/* Completely non-trivial. */
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template<typename T>
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struct optional_storage<T, false, false, false, false> : public optstore_helper<T> {
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using optstore_helper<T>::optstore_helper;
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constexpr optional_storage() noexcept = default;
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constexpr optional_storage(const optional_storage &rhs) NOEXCEPT_AS(_this->construct(rhs.mValue))
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{ if(rhs.mHasValue) this->construct(rhs.mValue); }
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constexpr optional_storage(optional_storage&& rhs) NOEXCEPT_AS(_this->construct(std::move(rhs.mValue)))
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{ if(rhs.mHasValue) this->construct(std::move(rhs.mValue)); }
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constexpr optional_storage& operator=(const optional_storage &rhs) NOEXCEPT_AS(_this->assign(rhs))
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{ this->assign(rhs); return *this; }
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constexpr optional_storage& operator=(optional_storage&& rhs) NOEXCEPT_AS(_this->assign(std::move(rhs)))
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{ this->assign(std::move(rhs)); return *this; }
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};
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#undef _this
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} // namespace detail_
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#define REQUIRES(...) std::enable_if_t<(__VA_ARGS__),bool> = true
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template<typename T>
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class optional {
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using storage_t = detail_::optional_storage<T>;
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storage_t mStore{};
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public:
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using value_type = T;
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constexpr optional() = default;
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constexpr optional(const optional&) = default;
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constexpr optional(optional&&) = default;
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constexpr optional(nullopt_t) noexcept { }
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template<typename ...Args>
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constexpr explicit optional(in_place_t, Args&& ...args)
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NOEXCEPT_AS(storage_t{al::in_place, std::forward<Args>(args)...})
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: mStore{al::in_place, std::forward<Args>(args)...}
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{ }
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template<typename U, REQUIRES(std::is_constructible<T, U&&>::value
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&& !std::is_same<std::decay_t<U>, al::in_place_t>::value
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&& !std::is_same<std::decay_t<U>, optional<T>>::value
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&& std::is_convertible<U&&, T>::value)>
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constexpr optional(U&& rhs) NOEXCEPT_AS(storage_t{al::in_place, std::forward<U>(rhs)})
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: mStore{al::in_place, std::forward<U>(rhs)}
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{ }
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template<typename U, REQUIRES(std::is_constructible<T, U&&>::value
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&& !std::is_same<std::decay_t<U>, al::in_place_t>::value
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&& !std::is_same<std::decay_t<U>, optional<T>>::value
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&& !std::is_convertible<U&&, T>::value)>
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constexpr explicit optional(U&& rhs) NOEXCEPT_AS(storage_t{al::in_place, std::forward<U>(rhs)})
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: mStore{al::in_place, std::forward<U>(rhs)}
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{ }
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~optional() = default;
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constexpr optional& operator=(const optional&) = default;
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constexpr optional& operator=(optional&&) = default;
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constexpr optional& operator=(nullopt_t) noexcept { mStore.reset(); return *this; }
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template<typename U=T>
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constexpr std::enable_if_t<std::is_constructible<T, U>::value
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&& std::is_assignable<T&, U>::value
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&& !std::is_same<std::decay_t<U>, optional<T>>::value
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&& (!std::is_same<std::decay_t<U>, T>::value || !std::is_scalar<U>::value),
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optional&> operator=(U&& rhs)
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{
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if(mStore.mHasValue)
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mStore.mValue = std::forward<U>(rhs);
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else
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mStore.construct(std::forward<U>(rhs));
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return *this;
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}
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constexpr const T* operator->() const { return std::addressof(mStore.mValue); }
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constexpr T* operator->() { return std::addressof(mStore.mValue); }
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constexpr const T& operator*() const& { return mStore.mValue; }
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constexpr T& operator*() & { return mStore.mValue; }
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constexpr const T&& operator*() const&& { return std::move(mStore.mValue); }
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constexpr T&& operator*() && { return std::move(mStore.mValue); }
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constexpr explicit operator bool() const noexcept { return mStore.mHasValue; }
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constexpr bool has_value() const noexcept { return mStore.mHasValue; }
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constexpr T& value() & { return mStore.mValue; }
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constexpr const T& value() const& { return mStore.mValue; }
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constexpr T&& value() && { return std::move(mStore.mValue); }
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constexpr const T&& value() const&& { return std::move(mStore.mValue); }
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template<typename U>
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constexpr T value_or(U&& defval) const&
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{ return bool{*this} ? **this : static_cast<T>(std::forward<U>(defval)); }
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template<typename U>
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constexpr T value_or(U&& defval) &&
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{ return bool{*this} ? std::move(**this) : static_cast<T>(std::forward<U>(defval)); }
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template<typename ...Args>
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constexpr T& emplace(Args&& ...args)
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{
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mStore.reset();
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mStore.construct(std::forward<Args>(args)...);
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return mStore.mValue;
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}
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template<typename U, typename ...Args>
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constexpr std::enable_if_t<std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value,
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T&> emplace(std::initializer_list<U> il, Args&& ...args)
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{
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mStore.reset();
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mStore.construct(il, std::forward<Args>(args)...);
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return mStore.mValue;
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}
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constexpr void reset() noexcept { mStore.reset(); }
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};
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template<typename T>
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constexpr optional<std::decay_t<T>> make_optional(T&& arg)
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{ return optional<std::decay_t<T>>{in_place, std::forward<T>(arg)}; }
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template<typename T, typename... Args>
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constexpr optional<T> make_optional(Args&& ...args)
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{ return optional<T>{in_place, std::forward<Args>(args)...}; }
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template<typename T, typename U, typename... Args>
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constexpr optional<T> make_optional(std::initializer_list<U> il, Args&& ...args)
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{ return optional<T>{in_place, il, std::forward<Args>(args)...}; }
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#undef REQUIRES
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#undef NOEXCEPT_AS
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} // namespace al
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#endif /* AL_OPTIONAL_H */
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