A template representing an optional value. More...

#include <optional.h>

Inheritance diagram for isc::util::Optional< T >:

Public Types
typedef T	ValueType
	Type of the encapsulated value.

Public Member Functions
	Optional ()
	Default constructor.

	Optional ()
	Specialization of the default `Optional` constructor for strings.

template<typename A >
	Optional (A value, const bool unspecified=false)
	Constructor.

bool	empty () const
	Checks if the encapsulated value is empty.

bool	empty () const
	Specialization of the `Optional::empty` method for strings.

T	get () const
	Retrieves the encapsulated value.

	operator T () const
	Type cast operator.

bool	operator!= (const T &other) const
	Inequality operator.

template<typename A >
Optional< T > &	operator= (A other)
	Assigns a new value value and marks it "specified".

bool	operator== (const T &other) const
	Equality operator.

bool	unspecified () const
	Checks if the value has been specified or unspecified.

void	unspecified (bool unspecified)
	Modifies the flag that indicates whether the value is specified or unspecified.

T	valueOr (T const &or_value) const
	Retrieves the encapsulated value if specified, or the given value otherwise.

Protected Attributes
T	default_
	Encapsulated value.

bool	unspecified_
	Flag which indicates if the value is specified.

Detailed Description

template<typename T>
class isc::util::Optional< T >

A template representing an optional value.

This template class encapsulates an optional value. The default implementation encapsulates numeric values, but additional specializations are defined as necessary to support other types od data.

This class includes a boolean flag which indicates if the encapsulated value is specified or unspecified. For example, a configuration parser for the DHCP server may use this class to represent a value of the configuration parameter which may appear in the configuration file, but is not mandatory. The value of the Optional may be initialized to "unspecified" initially. When the configuration parser finds that the particular parameter exists in the configuration file, the default value can be overridden and the value may be marked as "specified". If the parameter is not found, the value remains "unspecified" and the appropriate actions may be taken, e.g. the default value may be used.

Template Parameters

Type	of the encapsulated value.

Definition at line 36 of file optional.h.

Member Typedef Documentation

◆ ValueType

template<typename T >

typedef T isc::util::Optional< T >::ValueType

Type of the encapsulated value.

Definition at line 40 of file optional.h.

Constructor & Destructor Documentation

◆ Optional() [1/3]

template<typename T >

isc::util::Optional< T >::Optional ( )

inline

Default constructor.

Sets the encapsulated value to 0 and marks it as "unspecified".

The caller must ensure that the constructor of the class T creates a valid object when invoked with 0 as an argument. For example, a std::string(0) compiles but will crash at runtime as 0 is not a valid pointer for the std::string(const char*) constructor. Therefore, the specialization of the Optional template for std::string is provided below. It uses std::string default constructor.

For any other type used with this template which doesn't come with an appropriate constructor, the caller must create a template specialization similar to the one provided for std::string below.

Definition at line 94 of file optional.h.

◆ Optional() [2/3]

template<typename T >

template<typename A >

isc::util::Optional< T >::Optional	(	A	value,
		const bool	unspecified = false )

inline

Constructor.

Sets an explicit value and marks it as "specified".

Template Parameters

A	Type of the value to be assigned. Typically this is `T`, but may also be a type that can be cast to `T`.

Parameters

value	value to be assigned.
unspecified	initial state. Default is "unspecified".

Definition at line 107 of file optional.h.

◆ Optional() [3/3]

isc::util::Optional< std::string >::Optional ( )

inline

Specialization of the default Optional constructor for strings.

It calls default string object constructor.

Definition at line 167 of file optional.h.

Member Function Documentation

◆ empty() [1/2]

template<typename T >

bool isc::util::Optional< T >::empty ( ) const

inline

Checks if the encapsulated value is empty.

This method can be overloaded in the template specializations that are dedicated to strings, vectors etc.

Exceptions

isc::InvalidOperation.

Definition at line 153 of file optional.h.

References isc_throw.

Referenced by isc::dhcp::Network::clientSupported().

◆ empty() [2/2]

bool isc::util::Optional< std::string >::empty ( ) const

inline

Specialization of the Optional::empty method for strings.

Returns: true if the value is empty, false otherwise.

Definition at line 175 of file optional.h.

◆ get()

template<typename T >

T isc::util::Optional< T >::get ( ) const

inline

Retrieves the encapsulated value.

Returns: the encapsulated value

Definition at line 114 of file optional.h.

References isc::util::Optional< T >::default_.

Referenced by isc::db::PsqlBindArray::addOptional(), isc::db::MySqlBinding::condCreateBool(), isc::db::MySqlBinding::condCreateFloat(), isc::db::MySqlBinding::condCreateInteger(), isc::process::ConfigControlInfo::equals(), isc::process::ConfigBase::merge(), isc::dhcp::ClientClassDef::toElement(), isc::dhcp::Network::toElement(), and isc::process::ConfigBase::toElement().

◆ operator T()

template<typename T >

isc::util::Optional< T >::operator T ( ) const

inline

Type cast operator.

This operator converts the optional value to the actual value being encapsulated.

Returns: Encapsulated value.

Definition at line 60 of file optional.h.

◆ operator!=()

template<typename T >

bool isc::util::Optional< T >::operator!= ( const T & other ) const

inline

Inequality operator.

Parameters

other value to be compared.

Definition at line 74 of file optional.h.

References isc::util::Optional< T >::default_.

◆ operator=()

template<typename T >

template<typename A >

Optional< T > & isc::util::Optional< T >::operator= ( A other )

inline

Assigns a new value value and marks it "specified".

Template Parameters

A	Type of the value to be assigned. Typically this is `T`, but may also be a type that can be cast to `T`.

Parameters

other new actual value.

Definition at line 48 of file optional.h.

References isc::util::Optional< T >::default_, and isc::util::Optional< T >::unspecified_.

◆ operator==()

template<typename T >

bool isc::util::Optional< T >::operator== ( const T & other ) const

inline

Equality operator.

Parameters

other value to be compared.

Definition at line 67 of file optional.h.

References isc::util::Optional< T >::default_.

◆ unspecified() [1/2]

template<typename T >

bool isc::util::Optional< T >::unspecified ( ) const

inline

Checks if the value has been specified or unspecified.

Returns: true if the value hasn't been specified, false otherwise.

Definition at line 143 of file optional.h.

References isc::util::Optional< T >::unspecified_.

Referenced by isc::util::Optional< T >::unspecified().

◆ unspecified() [2/2]

template<typename T >

void isc::util::Optional< T >::unspecified ( bool unspecified )

inline

Modifies the flag that indicates whether the value is specified or unspecified.

Parameters

unspecified new value of the flag. If it is true, the value is marked as unspecified, otherwise it is marked as specified.

Definition at line 136 of file optional.h.

References isc::util::Optional< T >::unspecified(), and isc::util::Optional< T >::unspecified_.

Referenced by isc::db::PsqlBindArray::addOptional(), isc::db::PsqlBindArray::addOptional(), isc::db::PsqlBindArray::addOptionalInet4(), isc::db::PsqlBindArray::addOptionalInet6(), isc::db::MySqlBinding::condCreateBool(), isc::db::MySqlBinding::condCreateFloat(), isc::db::MySqlBinding::condCreateInteger(), isc::dhcp::ClientClassDef::toElement(), isc::dhcp::Network::toElement(), isc::process::ConfigBase::toElement(), and isc::process::ConfigControlInfo::toElement().

Here is the call graph for this function:

◆ valueOr()

template<typename T >

T isc::util::Optional< T >::valueOr ( T const & or_value ) const

inline

Retrieves the encapsulated value if specified, or the given value otherwise.

Parameters

or_value the value it defaults to, if unspecified

Returns: the encapsulated value or the default value

Definition at line 124 of file optional.h.

References isc::util::Optional< T >::default_, and isc::util::Optional< T >::unspecified_.

Member Data Documentation

◆ default_

template<typename T >

T isc::util::Optional< T >::default_

protected

Encapsulated value.

Definition at line 158 of file optional.h.

Referenced by isc::util::Optional< T >::get(), isc::util::Optional< bool >::operator bool(), isc::util::Optional< T >::operator!=(), isc::util::Optional< T >::operator=(), isc::util::Optional< T >::operator==(), and isc::util::Optional< T >::valueOr().

◆ unspecified_

template<typename T >

bool isc::util::Optional< T >::unspecified_

protected

Flag which indicates if the value is specified.

Definition at line 159 of file optional.h.

Referenced by isc::util::Optional< T >::operator=(), isc::util::Optional< T >::unspecified(), isc::util::Optional< T >::unspecified(), and isc::util::Optional< T >::valueOr().

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

optional.h

Public Types

Public Member Functions

Protected Attributes

Detailed Description

Member Typedef Documentation

◆ ValueType

Constructor & Destructor Documentation

◆ Optional() [1/3]

◆ Optional() [2/3]

◆ Optional() [3/3]

Member Function Documentation

◆ empty() [1/2]

◆ empty() [2/2]

◆ get()

◆ operator T()

◆ operator!=()

◆ operator=()

◆ operator==()

◆ unspecified() [1/2]

◆ unspecified() [2/2]

◆ valueOr()

Member Data Documentation

◆ default_

◆ unspecified_