caf::maybe< T > Class Template Reference

Represents a computation returning either T or std::error_condition. More...

#include <maybe.hpp>

Public Types
using	type = typename std::remove_reference< T >::type
using	reference = type &
using	const_reference = const type &
using	pointer = type *
using	const_pointer = const type *
using	error_type = std::error_condition
using	storage = typename std::conditional< std::is_reference< T >::value, std::reference_wrapper< type >, T >::type
	Type for storing values.

Public Member Functions
	maybe (error_type err)
	Creates an instance representing an error.
	maybe (T value)
	Creates an instance representing value.
template<class E , class = typename std::enable_if< std::is_error_condition_enum<E>::value >::type>
	maybe (E error_code_enum)
	Creates an instance representing an error from an error condition enum. More...
	maybe ()
	Creates an empty instance.
	maybe (const none_t &)
	Creates an empty instance.
	maybe (const maybe &other)
	maybe (maybe &&other)
template<class U >
	maybe (maybe< U > &&other)
template<class U >
	maybe (const maybe< U > &other)
maybe &	operator= (const none_t &)
maybe &	operator= (T value)
maybe &	operator= (error_type err)
template<class E , class = typename std::enable_if< std::is_error_condition_enum<E>::value >::type>
maybe &	operator= (E error_code_enum)
maybe &	operator= (maybe &&other)
maybe &	operator= (const maybe &other)
template<class U >
maybe &	operator= (maybe< U > &&other)
template<class U >
maybe &	operator= (const maybe< U > &other)
bool	available () const
	Queries whether this instance holds a value.
	operator bool () const
	Returns available().
bool	operator! () const
	Returns ! available().
reference	get ()
	Returns the value.
const_reference	get () const
	Returns the value.
reference	operator* ()
	Returns the value.
const_reference	operator* () const
	Returns the value.
pointer	operator-> ()
	Returns a pointer to the value.
const_pointer	operator-> () const
	Returns a pointer to the value.
bool	empty () const
	Returns whether this objects holds neither a value nor an actual error.
const error_type &	error () const
	Returns the error.

Related Functions
(Note that these are not member functions.)
template<class T , typename U >
bool	operator== (const maybe< T > &lhs, const maybe< U > &rhs)
	Returns true if both objects represent either the same value or the same error, false otherwise.
template<class T , typename U >
bool	operator== (const T &lhs, const maybe< U > &rhs)
	Returns true if rhs is available and its value is equal to lhs.
template<class T , typename U >
bool	operator!= (const maybe< T > &lhs, const maybe< U > &rhs)
	Returns true if the objects represent different values or errors, false otherwise.
template<class T , typename U >
bool	operator!= (const maybe< T > &lhs, const U &rhs)
	Returns true if lhs is not available or its value is not equal to rhs.
template<class T , typename U >
bool	operator!= (const T &lhs, const maybe< U > &rhs)
	Returns true if rhs is not available or its value is not equal to lhs.
template<class T >
bool	operator== (const maybe< T > &val, const std::error_condition &err)
	Returns ! val.available() && val.error() == err.
template<class T >
bool	operator== (const std::error_condition &err, const maybe< T > &val)
	Returns ! val.available() && val.error() == err.
template<class T >
bool	operator!= (const maybe< T > &val, const std::error_condition &err)
	Returns val.available() || val.error() != err.
template<class T >
bool	operator!= (const std::error_condition &err, const maybe< T > &val)
	Returns val.available() || val.error() != err.
template<class T >
bool	operator== (const maybe< T > &val, const none_t &)
	Returns val.empty().
template<class T >
bool	operator== (const none_t &, const maybe< T > &val)
	Returns val.empty().
template<class T >
bool	operator!= (const maybe< T > &val, const none_t &)
	Returns ! val.empty().
template<class T >
bool	operator!= (const none_t &, const maybe< T > &val)
	Returns ! val.empty().

Detailed Description

template<class T>
class caf::maybe< T >

Represents a computation returning either T or std::error_condition.

Note that the error condition might be default-constructed. In this case, a maybe represents simply none. Hence, this type has three possible states:

• A value of T is available
  • available() returns true
  • empty() returns false
  • error() evaluates to false
• No value is available but no error occurred
  • available() returns false
  • empty() returns true
  • error() evaluates to false
• An error occurred (no value available)
  • available() returns false
  • empty() returns false
  • error() evaluates to true

Constructor & Destructor Documentation

template<class T>

template<class E , class = typename std::enable_if< std::is_error_condition_enum<E>::value >::type>

caf::maybe< T >::maybe

(

E

error_code_enum

)

Creates an instance representing an error from an error condition enum.

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

• libcaf_core/caf/fwd.hpp
• libcaf_core/caf/maybe.hpp