aurora::Optional< T > Class Template Reference

Represents optional values. More...

Public Member Functions
	Optional ()
	Construct empty optional with default constructor.
	Optional (NulloptType)
	Construct empty optional from aurora::nullopt.
template<typename... Args>
	Optional (InplaceType, Args &&...args)
	Construct object in-place, forwarding arguments.
	Optional (T object)
	Construct implicitly from T object (move or copy)
	Optional (const Optional &origin)
	Copy constructor.
	Optional (Optional &&source)
	Move constructor.
Optional &	operator= (T object)
	Assign from T object (move or copy)
Optional &	operator= (const Optional &origin)
	Copy assignment operator.
Optional &	operator= (Optional &&source)
	Move assignment operator.
	~Optional ()
	Destructor.
void	swap (Optional &other)
	Swaps two optional objects.
T &	operator* ()
	Returns the contained object. More...
const T &	operator* () const
	Returns the contained object (const overload). More...
T *	operator-> ()
	Returns the contained object for member access. More...
const T *	operator-> () const
	Returns the contained object for member access (const overload). More...
	operator SafeBool () const
	Check if the optional object contains a value.

Related Functions
(Note that these are not member functions.)
template<typename T >
void	swap (Optional< T > &lhs, Optional< T > &rhs)
	Swaps two optionals.
template<typename T , typename... Args>
Optional< T >	makeOptional (Args &&...args)
	Emplaces an object directly inside the aurora::Optional object. More...
template<typename T >
bool	operator== (const Optional< T > &lhs, const Optional< T > &rhs)
	Equality comparison. More...
template<typename T >
bool	operator!= (const Optional< T > &lhs, const Optional< T > &rhs)
	Inequality comparison. More...

Detailed Description

template<typename T>
class aurora::Optional< T >

Represents optional values.

This class extends objects with an additional null state, which explicitly denotes the absence of a valid object. There are many situations where an object can either carry a valid state or none, especially in function return values. For example, let's assume we have a function find() that searches for a T object, but doesn't always find one. C++ offers many ways to deal with this situation, but the usual ones come with certain drawbacks:

• T* find() – the pointer must refer to a stored object (no temporary) or require dynamic allocation
• iterator find() + comparison with end() – requires an underlying container and exposes implementation details
• bool has() + T find() – requires two calls, thus two possibly expensive searches instead of one
• bool find(T& out) – user must construct T up-front, requiring a default constructor, incurring useless initialization and preventing const qualifier

This class offers a new way:

• Optional<T> find()

The syntax is very similar to a pointer, with dereferencing operators and conversion to bool contexts:

aurora::Optional<T> opt = find();
if (opt) // check if 'opt' has a value
    use(*opt); // dereference 'opt' to access the T object

You can even simplify this code further, using type inference and the little-known C++ feature of declarations inside if statements:

if (auto opt = find())
    use(*opt);

This class can be used as an interim solution until std::optional becomes part of a C++ standard and is supported by all major compilers. aurora::Optional uses a very similar (although slightly smaller) API.

Member Function Documentation

template<typename T>

T& aurora::Optional< T >::operator*

(

)

Returns the contained object.

Warning

Dereferencing empty optionals yields undefined behavior.

template<typename T>

const T& aurora::Optional< T >::operator*

(

)

const

Returns the contained object (const overload).

Warning

Dereferencing empty optionals yields undefined behavior.

template<typename T>

T* aurora::Optional< T >::operator->

(

)

Returns the contained object for member access.

Warning

Dereferencing empty optionals yields undefined behavior.

template<typename T>

const T* aurora::Optional< T >::operator->

(

)

const

Returns the contained object for member access (const overload).

Warning

Dereferencing empty optionals yields undefined behavior.

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The documentation for this class was generated from the following file:

• Tools/Optional.hpp