google::cloud::v0::optional< T > Class Template Reference

A poor's man version of std::optional<T>. More...

#include <google/cloud/optional.h>

Public Member Functions
	optional ()
	optional (T const &x)
	optional (T &&x) noexcept
	optional (optional< T > &&rhs) noexcept
	optional (optional< T > const &rhs)
	~optional ()
optional &	operator= (optional< T > const &rhs)
optional &	operator= (optional< T > &&rhs) noexcept
template<typename U = T>
std::enable_if< not std::is_same< optional, typename std::decay< U >::type >::value, optional >::type &	operator= (U &&rhs)
constexpr T const *	operator-> () const
T *	operator-> ()
constexpr T const &	operator* () const &
T &	operator* () &
T &&	operator* () &&
T &	value () &
T const &	value () const &
T &&	value () &&
T const &&	value () const &&
template<typename U >
constexpr T	value_or (U &&default_value) const &
template<typename U >
T	value_or (U &&default_value) &&
	operator bool () const
bool	has_value () const
void	reset ()
T &	emplace (T &&value)
bool	operator== (optional const &rhs) const
bool	operator!= (optional const &rhs) const
bool	operator< (optional const &rhs) const
bool	operator> (optional const &rhs) const
bool	operator>= (optional const &rhs) const
bool	operator<= (optional const &rhs) const

Detailed Description

template<typename T>
class google::cloud::v0::optional< T >

A poor's man version of std::optional<T>.

This project needs to support C++11 and C++14, so std::optional<> is not available. We cannot use Abseil either, see #232 for the reasons. So we implement a very minimal "optional" class that documents the intent and we will remove it when possible.

Template Parameters

T	the type of the optional value.

Warning

this is not a drop-in replacement for std::optional<>, it has at least the following defects:

• it raises std::logic_error instead of std::bad_optional_access.
• emplace() is a very simple version.
• It does not have the full complement of assignment operators and constructors required by the standard.
• It lacks comparison operators.
• No nullopt_t.
• No std::swap(), std::make_optional(), or std::hash().

Some of the member functions have a (commented-out) constexpr qualifier. The spec requires them to be constexpr functions, but the spec assumes C++14 (or newer) semantics for non-const constexpr member functions, and we often compile with C++11 semantics.

TODO(#687) - replace with absl::optional<> or std::optional<> when possible.

Definition at line 53 of file optional.h.

Constructor & Destructor Documentation

optional() [1/5]

template<typename T >

google::cloud::v0::optional< T >::optional ( )

inline

Definition at line 55 of file optional.h.

optional() [2/5]

template<typename T >

google::cloud::v0::optional< T >::optional ( T const &  x )

inlineexplicit

Definition at line 56 of file optional.h.

optional() [3/5]

template<typename T >

google::cloud::v0::optional< T >::optional ( T &&  x )

inlineexplicitnoexcept

Definition at line 59 of file optional.h.

optional() [4/5]

template<typename T >

google::cloud::v0::optional< T >::optional ( optional< T > &&  rhs )

inlinenoexcept

Definition at line 62 of file optional.h.

optional() [5/5]

template<typename T >

google::cloud::v0::optional< T >::optional ( optional< T > const &  rhs )

inline

Definition at line 67 of file optional.h.

~optional()

template<typename T >

google::cloud::v0::optional< T >::~optional ( )

inline

Definition at line 72 of file optional.h.

Member Function Documentation

emplace()

template<typename T >

T& google::cloud::v0::optional< T >::emplace ( T &&  value )

inline

Definition at line 194 of file optional.h.

has_value()

template<typename T >

bool google::cloud::v0::optional< T >::has_value ( ) const

inline

Definition at line 186 of file optional.h.

operator bool()

template<typename T >

google::cloud::v0::optional< T >::operator bool ( ) const

inline

Definition at line 185 of file optional.h.

operator!=()

template<typename T >

bool google::cloud::v0::optional< T >::operator!= ( optional< T > const &  rhs ) const

inline

Definition at line 211 of file optional.h.

operator*() [1/3]

template<typename T >

constexpr T const& google::cloud::v0::optional< T >::operator* ( ) const &

inline

Definition at line 141 of file optional.h.

operator*() [2/3]

template<typename T >

T& google::cloud::v0::optional< T >::operator* ( ) &

inline

Definition at line 144 of file optional.h.

operator*() [3/3]

template<typename T >

T&& google::cloud::v0::optional< T >::operator* ( ) &&

inline

Definition at line 151 of file optional.h.

operator->() [1/2]

template<typename T >

constexpr T const* google::cloud::v0::optional< T >::operator-> ( ) const

inline

Definition at line 137 of file optional.h.

operator->() [2/2]

template<typename T >

T* google::cloud::v0::optional< T >::operator-> ( )

inline

Definition at line 140 of file optional.h.

operator<()

template<typename T >

bool google::cloud::v0::optional< T >::operator< ( optional< T > const &  rhs ) const

inline

Definition at line 215 of file optional.h.

operator<=()

template<typename T >

bool google::cloud::v0::optional< T >::operator<= ( optional< T > const &  rhs ) const

inline

Definition at line 237 of file optional.h.

operator=() [1/3]

template<typename T >

optional& google::cloud::v0::optional< T >::operator= ( optional< T > const &  rhs )

inline

Definition at line 74 of file optional.h.

operator=() [2/3]

template<typename T >

optional& google::cloud::v0::optional< T >::operator= ( optional< T > &&  rhs )

inlinenoexcept

Definition at line 95 of file optional.h.

operator=() [3/3]

template<typename T >

template<typename U = T>

std::enable_if< not std::is_same<optional, typename std::decay<U>::type>::value, optional>::type& google::cloud::v0::optional< T >::operator= ( U &&  rhs )

inline

Definition at line 123 of file optional.h.

operator==()

template<typename T >

bool google::cloud::v0::optional< T >::operator== ( optional< T > const &  rhs ) const

inline

Definition at line 201 of file optional.h.

operator>()

template<typename T >

bool google::cloud::v0::optional< T >::operator> ( optional< T > const &  rhs ) const

inline

Definition at line 229 of file optional.h.

operator>=()

template<typename T >

bool google::cloud::v0::optional< T >::operator>= ( optional< T > const &  rhs ) const

inline

Definition at line 233 of file optional.h.

reset()

template<typename T >

void google::cloud::v0::optional< T >::reset ( )

inline

Definition at line 188 of file optional.h.

value() [1/4]

template<typename T >

T& google::cloud::v0::optional< T >::value ( ) &

inline

Definition at line 155 of file optional.h.

value() [2/4]

template<typename T >

T const& google::cloud::v0::optional< T >::value ( ) const &

inline

Definition at line 159 of file optional.h.

value() [3/4]

template<typename T >

T&& google::cloud::v0::optional< T >::value ( ) &&

inline

Definition at line 163 of file optional.h.

value() [4/4]

template<typename T >

T const&& google::cloud::v0::optional< T >::value ( ) const &&

inline

Definition at line 168 of file optional.h.

value_or() [1/2]

template<typename T >

template<typename U >

constexpr T google::cloud::v0::optional< T >::value_or ( U &&  default_value ) const &

inline

Definition at line 174 of file optional.h.

value_or() [2/2]

template<typename T >

template<typename U >

T google::cloud::v0::optional< T >::value_or ( U &&  default_value ) &&

inline

Definition at line 180 of file optional.h.