Overview

template<typename T, OptionalState auto kHasValueState, bool IsTriviallyDestructible = std::is_trivially_destructible_v<T>>
class pw::containers::internal::Optional< T, kHasValueState, IsTriviallyDestructible >

Optional is similar to std::optional and pw::Result, but uses a user-specified state type for object presence. One state value is reserved to indicate that the object is present.

Optional is essentially a customizable pw::Result, supporting custom enums instead of only pw::Status. pw::Result cannot easily wrap a pw::Status, so is not suitable as a general T wrapper. Construction or assignment from a Status is ambiguous, since it is unclear if the Status is a value or an error. These issues apply to absl::StatusOr as well (see b/280392796). Optional resolves this by prohibiting conversions between the value and state type and with a simpler construction/assignment API.

To simplify its use in templates, Optional is specialized for void.

Template Parameters

T	type of the optional value
kHasValueState	State value that represents

Inheritance diagram for pw::containers::internal::Optional< T, kHasValueState, IsTriviallyDestructible >:

Public Types
using	state_type = decltype(kHasValueState)

using	value_type = T

Public Member Functions
constexpr	Optional (state_type state)
	Constructs an optional without a value using the provided state.

constexpr	Optional (const value_type &value)
	Constructs an optional containing a value.

constexpr	Optional (value_type &&value)

template<typename... Args>
constexpr	Optional (std::in_place_t, Args &&... args)
	Constructs an optional in-place containing a value.

constexpr	Optional (const Optional &)=default

constexpr Optional &	operator= (const Optional &)=default

constexpr	Optional (Optional &&)=default

constexpr Optional &	operator= (Optional &&)=default

template<typename U , std::enable_if_t< std::conjunction_v< std::negation< std::is_same< T, U > >, std::is_constructible< T, const U & >, std::is_convertible< const U &, T > >, int > = 0>
constexpr	Optional (const Optional< U, kHasValueState > &other)
	Constructs an optional from another optional with a compatible value type.

template<typename U , std::enable_if_t< std::conjunction_v< std::negation< std::is_same< T, U > >, std::is_constructible< T, const U & >, std::negation< std::is_convertible< const U &, T > > >, int > = 0>
constexpr	Optional (const Optional< U, kHasValueState > &other)

template<typename U , std::enable_if_t< std::conjunction_v< std::negation< std::is_same< T, U > >, std::is_constructible< T, U && >, std::is_convertible< U &&, T > >, int > = 0>
constexpr	Optional (Optional< U, kHasValueState > &&other)

template<typename U , std::enable_if_t< std::conjunction_v< std::negation< std::is_same< T, U > >, std::is_constructible< T, U && >, std::negation< std::is_convertible< U &&, T > > >, int > = 0>
constexpr	Optional (Optional< U, kHasValueState > &&other)

constexpr Optional &	operator= (const value_type &value)
	Assigns a new value to the optional.

constexpr Optional &	operator= (value_type &&value)
	Move assigns a new value to the optional.

template<typename... Args>
constexpr void	emplace (Args &&... args)
	Constructs a new value in-place.

constexpr void	reset (state_type state)

template<state_type kState>
constexpr void	reset ()

constexpr bool	has_value () const
	Returns true if the optional contains a value.

constexpr T &	operator* () &

constexpr const T &	operator* () const &

constexpr T &&	operator* () &&

constexpr const T &&	operator* () const &&

constexpr T *	operator-> ()

constexpr const T *	operator-> () const

constexpr T &	value () &
	Returns the contained value. Asserts if the value is not present.

constexpr const T &	value () const &
	Returns the contained value. Asserts if the value is not present.

constexpr T &&	value () &&
	Returns the contained value. Asserts if the value is not present.

constexpr const T &&	value () const &&
	Returns the contained value. Asserts if the value is not present.

constexpr state_type	state () const
	Returns the state. Always valid, whether `has_value` is `true` or `false`.

Friends
constexpr bool	operator== (const Optional &lhs, const Optional &rhs)

constexpr bool	operator!= (const Optional &lhs, const Optional &rhs)

constexpr bool	operator== (const Optional &lhs, const T &rhs)

constexpr bool	operator== (const T &lhs, const Optional &rhs)

constexpr bool	operator!= (const Optional &lhs, const T &rhs)

constexpr bool	operator!= (const T &lhs, const Optional &rhs)