1411 lines
43 KiB
Plaintext
1411 lines
43 KiB
Plaintext
[/
|
|
Boost.Optional
|
|
|
|
Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
|
|
|
|
Distributed under the Boost Software License, Version 1.0.
|
|
(See accompanying file LICENSE_1_0.txt or copy at
|
|
http://www.boost.org/LICENSE_1_0.txt)
|
|
]
|
|
|
|
|
|
[section Detailed Semantics - Optional Values]
|
|
|
|
[note
|
|
The following section contains various `assert()` which are used only to show
|
|
the postconditions as sample code. It is not implied that the type `T` must
|
|
support each particular expression but that if the expression is supported,
|
|
the implied condition holds.
|
|
]
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor]
|
|
|
|
[: `optional<T>::optional() noexcept;`]
|
|
|
|
* [*Effect:] Default-Constructs an `optional`.
|
|
* [*Postconditions:] `*this` is [_uninitialized].
|
|
* [*Notes:] T's default constructor [_is not] called.
|
|
* [*Example:]
|
|
``
|
|
optional<T> def ;
|
|
assert ( !def ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_none_t]
|
|
|
|
[: `optional<T>::optional( none_t ) noexcept;`]
|
|
|
|
* [*Effect:] Constructs an `optional` uninitialized.
|
|
* [*Postconditions:] `*this` is [_uninitialized].
|
|
* [*Notes:] `T`'s default constructor [_is not] called. The expression
|
|
`boost::none` denotes an instance of `boost::none_t` that can be used as
|
|
the parameter.
|
|
* [*Example:]
|
|
``
|
|
#include <boost/none.hpp>
|
|
optional<T> n(none) ;
|
|
assert ( !n ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_value]
|
|
|
|
[: `optional<T>::optional( T const& v )`]
|
|
|
|
* [*Requires:] `is_copy_constructible<T>::value` is `true`.
|
|
* [*Effect:] Directly-Constructs an `optional`.
|
|
* [*Postconditions:] `*this` is [_initialized] and its value is a ['copy]
|
|
of `v`.
|
|
* [*Throws:] Whatever `T::T( T const& )` throws.
|
|
* [*Notes: ] `T::T( T const& )` is called.
|
|
* [*Exception Safety:] Exceptions can only be thrown during
|
|
`T::T( T const& );` in that case, this constructor has no effect.
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt(v);
|
|
assert ( *opt == v ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_move_value]
|
|
|
|
[: `optional<T>::optional( T&& v )`]
|
|
|
|
* [*Requires:] `is_move_constructible<T>::value` is `true`.
|
|
* [*Effect:] Directly-Move-Constructs an `optional`.
|
|
* [*Postconditions:] `*this` is [_initialized] and its value is move-constructed from `v`.
|
|
* [*Throws:] Whatever `T::T( T&& )` throws.
|
|
* [*Notes: ] `T::T( T&& )` is called.
|
|
* [*Exception Safety:] Exceptions can only be thrown during
|
|
`T::T( T&& );` in that case, the state of `v` is determined by exception safety guarantees for `T::T(T&&)`.
|
|
* [*Example:]
|
|
``
|
|
T v1, v2;
|
|
optional<T> opt(std::move(v1));
|
|
assert ( *opt == v2 ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_bool_value]
|
|
|
|
[: `optional<T>::optional( bool condition, T const& v ) ;` ]
|
|
|
|
* If condition is true, same as:
|
|
|
|
[: `optional<T>::optional( T const& v )`]
|
|
|
|
* otherwise, same as:
|
|
|
|
[: `optional<T>::optional()`]
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_optional]
|
|
|
|
[: `optional<T>::optional( optional const& rhs );`]
|
|
|
|
* [*Requires:] `is_copy_constructible<T>::value` is `true`.
|
|
* [*Effect:] Copy-Constructs an `optional`.
|
|
* [*Postconditions:] If rhs is initialized, `*this` is initialized and
|
|
its value is a ['copy] of the value of `rhs`; else `*this` is uninitialized.
|
|
* [*Throws:] Whatever `T::T( T const& )` throws.
|
|
* [*Notes:] If rhs is initialized, `T::T(T const& )` is called.
|
|
* [*Exception Safety:] Exceptions can only be thrown during
|
|
`T::T( T const& );` in that case, this constructor has no effect.
|
|
* [*Example:]
|
|
``
|
|
optional<T> uninit ;
|
|
assert (!uninit);
|
|
|
|
optional<T> uinit2 ( uninit ) ;
|
|
assert ( uninit2 == uninit );
|
|
|
|
optional<T> init( T(2) );
|
|
assert ( *init == T(2) ) ;
|
|
|
|
optional<T> init2 ( init ) ;
|
|
assert ( init2 == init ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_move_constructor_optional]
|
|
|
|
[: `optional<T>::optional( optional&& rhs ) noexcept(`['see below]`);`]
|
|
|
|
* [*Requires:] `is_move_constructible<T>::value` is `true`.
|
|
* [*Effect:] Move-constructs an `optional`.
|
|
* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and
|
|
its value is move constructed from `rhs`; else `*this` is uninitialized.
|
|
* [*Throws:] Whatever `T::T( T&& )` throws.
|
|
* [*Remarks:] The expression inside `noexcept` is equivalent to `is_nothrow_move_constructible<T>::value`.
|
|
* [*Notes:] If `rhs` is initialized, `T::T( T && )` is called.
|
|
* [*Exception Safety:] Exceptions can only be thrown during
|
|
`T::T( T&& );` in that case, `rhs` remains initialized and the value of `*rhs` is determined by exception safety of `T::T(T&&)`.
|
|
* [*Example:]
|
|
``
|
|
optional<std::unique_ptr<T>> uninit ;
|
|
assert (!uninit);
|
|
|
|
optional<std::unique_ptr<T>> uinit2 ( std::move(uninit) ) ;
|
|
assert ( uninit2 == uninit );
|
|
|
|
optional<std::unique_ptr<T>> init( std::uniqye_ptr<T>(new T(2)) );
|
|
assert ( **init == T(2) ) ;
|
|
|
|
optional<std::unique_ptr<T>> init2 ( std::move(init) ) ;
|
|
assert ( init );
|
|
assert ( *init == nullptr );
|
|
assert ( init2 );
|
|
assert ( **init2 == T(2) ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_other_optional]
|
|
|
|
[: `template<U> explicit optional<T>::optional( optional<U> const& rhs );`]
|
|
|
|
* [*Effect:] Copy-Constructs an `optional`.
|
|
* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
|
|
value is a ['copy] of the value of rhs converted to type `T`; else `*this` is
|
|
uninitialized.
|
|
* [*Throws:] Whatever `T::T( U const& )` throws.
|
|
* [*Notes: ] `T::T( U const& )` is called if `rhs` is initialized, which requires a
|
|
valid conversion from `U` to `T`.
|
|
* [*Exception Safety:] Exceptions can only be thrown during `T::T( U const& );`
|
|
in that case, this constructor has no effect.
|
|
* [*Example:]
|
|
``
|
|
optional<double> x(123.4);
|
|
assert ( *x == 123.4 ) ;
|
|
|
|
optional<int> y(x) ;
|
|
assert( *y == 123 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_move_constructor_other_optional]
|
|
|
|
[: `template<U> explicit optional<T>::optional( optional<U>&& rhs );`]
|
|
|
|
* [*Effect:] Move-constructs an `optional`.
|
|
* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
|
|
value is move-constructed from `*rhs`; else `*this` is
|
|
uninitialized.
|
|
* [*Throws:] Whatever `T::T( U&& )` throws.
|
|
* [*Notes: ] `T::T( U&& )` is called if `rhs` is initialized, which requires a
|
|
valid conversion from `U` to `T`.
|
|
* [*Exception Safety:] Exceptions can only be thrown during `T::T( U&& );`
|
|
in that case, `rhs` remains initialized and the value of `*rhs` is determined by exception safety guarantee of `T::T( U&& )`.
|
|
* [*Example:]
|
|
``
|
|
optional<double> x(123.4);
|
|
assert ( *x == 123.4 ) ;
|
|
|
|
optional<int> y(std::move(x)) ;
|
|
assert( *y == 123 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_in_place_init]
|
|
|
|
[: `template<class... Args> explicit optional<T>::optional( in_place_init_t, Args&&... ars );`]
|
|
|
|
* [*Requires:] `is_constructible_v<T, Args&&...>` is `true`.
|
|
* [*Effect:] Initializes the contained value as if direct-non-list-initializing an object of type `T` with the
|
|
arguments `std::forward<Args>(args)...`.
|
|
* [*Postconditions:] `*this` is initialized.
|
|
* [*Throws:] Any exception thrown by the selected constructor of `T`.
|
|
* [*Notes: ] `T` need not be __MOVE_CONSTRUCTIBLE__. On compilers that do not suppor variadic templates or rvalue references, this constuctor is available in limited functionality. For details [link optional_emplace_workaround see here].
|
|
|
|
* [*Example:]
|
|
``
|
|
// creates an std::mutex using its default constructor
|
|
optional<std::mutex> om {in_place_init};
|
|
assert (om);
|
|
|
|
// creates a unique_lock by calling unique_lock(*om, std::defer_lock)
|
|
optional<std::unique_lock<std::mutex>> ol {in_place_init, *om, std::defer_lock};
|
|
assert (ol);
|
|
assert (!ol->owns_lock());
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_in_place_init_if]
|
|
|
|
[: `template<class... Args> explicit optional<T>::optional( in_place_init_if_t, bool condition, Args&&... ars );`]
|
|
|
|
* [*Requires:] `is_constructible_v<T, Args&&...>` is `true`.
|
|
* [*Effect:] If `condition` is `true`, initializes the contained value as if direct-non-list-initializing an object of type `T` with the arguments `std::forward<Args>(args)...`.
|
|
* [*Postconditions:] `bool(*this) == condition`.
|
|
* [*Throws:] Any exception thrown by the selected constructor of `T`.
|
|
* [*Notes: ] `T` need not be __MOVE_CONSTRUCTIBLE__. On compilers that do not suppor variadic templates or rvalue references, this constuctor is available in limited functionality. For details [link optional_emplace_workaround see here].
|
|
|
|
* [*Example:]
|
|
``
|
|
optional<std::vector<std::string>> ov1 {in_place_init_if, false, 3, "A"};
|
|
assert (!ov1);
|
|
|
|
optional<std::vector<std::string>> ov2 {in_place_init_if, true, 3, "A"};
|
|
assert (ov2);
|
|
assert (ov2->size() == 3);
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_constructor_factory]
|
|
|
|
[: `template<InPlaceFactory> explicit optional<T>::optional( InPlaceFactory const& f );`]
|
|
[: `template<TypedInPlaceFactory> explicit optional<T>::optional( TypedInPlaceFactory const& f );`]
|
|
|
|
* [*Effect:] Constructs an `optional` with a value of `T` obtained from the
|
|
factory.
|
|
* [*Postconditions: ] `*this` is [_initialized] and its value is ['directly given]
|
|
from the factory `f` (i.e., the value [_is not copied]).
|
|
* [*Throws:] Whatever the `T` constructor called by the factory throws.
|
|
* [*Notes:] See [link boost_optional.tutorial.in_place_factories In-Place Factories]
|
|
* [*Exception Safety:] Exceptions can only be thrown during the call to
|
|
the `T` constructor used by the factory; in that case, this constructor has
|
|
no effect.
|
|
* [*Example:]
|
|
``
|
|
class C { C ( char, double, std::string ) ; } ;
|
|
|
|
C v('A',123.4,"hello");
|
|
|
|
optional<C> x( in_place ('A', 123.4, "hello") ); // InPlaceFactory used
|
|
optional<C> y( in_place<C>('A', 123.4, "hello") ); // TypedInPlaceFactory used
|
|
|
|
assert ( *x == v ) ;
|
|
assert ( *y == v ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_equal_none_t]
|
|
|
|
[: `optional& optional<T>::operator= ( none_t ) noexcept;`]
|
|
|
|
* [*Effect:] If `*this` is initialized destroys its contained value.
|
|
* [*Postconditions: ] `*this` is uninitialized.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_equal_value]
|
|
|
|
[: `optional& optional<T>::operator= ( T const& rhs ) ;`]
|
|
|
|
* [*Effect:] Assigns the value `rhs` to an `optional`.
|
|
* [*Postconditions: ] `*this` is initialized and its value is a ['copy] of `rhs`.
|
|
* [*Throws:] Whatever `T::operator=( T const& )` or `T::T(T const&)` throws.
|
|
* [*Notes:] If `*this` was initialized, `T`'s assignment operator is used,
|
|
otherwise, its copy-constructor is used.
|
|
* [*Exception Safety:] In the event of an exception, the initialization
|
|
state of `*this` is unchanged and its value unspecified as far as `optional`
|
|
is concerned (it is up to `T`'s `operator=()`). If `*this` is initially
|
|
uninitialized and `T`'s ['copy constructor] fails, `*this` is left properly
|
|
uninitialized.
|
|
* [*Example:]
|
|
``
|
|
T x;
|
|
optional<T> def ;
|
|
optional<T> opt(x) ;
|
|
|
|
T y;
|
|
def = y ;
|
|
assert ( *def == y ) ;
|
|
opt = y ;
|
|
assert ( *opt == y ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_move_equal_value]
|
|
|
|
[: `optional& optional<T>::operator= ( T&& rhs ) ;`]
|
|
|
|
* [*Effect:] Moves the value `rhs` to an `optional`.
|
|
* [*Postconditions: ] `*this` is initialized and its value is moved from `rhs`.
|
|
* [*Throws:] Whatever `T::operator=( T&& )` or `T::T(T &&)` throws.
|
|
* [*Notes:] If `*this` was initialized, `T`'s move-assignment operator is used,
|
|
otherwise, its move-constructor is used.
|
|
* [*Exception Safety:] In the event of an exception, the initialization
|
|
state of `*this` is unchanged and its value unspecified as far as `optional`
|
|
is concerned (it is up to `T`'s `operator=()`). If `*this` is initially
|
|
uninitialized and `T`'s ['move constructor] fails, `*this` is left properly
|
|
uninitialized.
|
|
* [*Example:]
|
|
``
|
|
T x;
|
|
optional<T> def ;
|
|
optional<T> opt(x) ;
|
|
|
|
T y1, y2, yR;
|
|
def = std::move(y1) ;
|
|
assert ( *def == yR ) ;
|
|
opt = std::move(y2) ;
|
|
assert ( *opt == yR ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_equal_optional]
|
|
|
|
[: `optional& optional<T>::operator= ( optional const& rhs ) ;`]
|
|
|
|
* [*Requires:] `T` is __COPY_CONSTRUCTIBLE__ and `CopyAssignable`.
|
|
* [*Effects:]
|
|
[table
|
|
[]
|
|
[[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
|
|
[[[*`rhs` contains a value]][assigns `*rhs` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `*rhs`]]
|
|
[[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
|
|
]
|
|
* [*Returns:] `*this`;
|
|
* [*Postconditions:] `bool(rhs) == bool(*this)`.
|
|
* [*Exception Safety:] If any exception is thrown, the initialization state of `*this` and `rhs` remains unchanged.
|
|
If an exception is thrown during the call to `T`'s copy constructor, no effect.
|
|
If an exception is thrown during the call to `T`'s copy assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt(v);
|
|
optional<T> def ;
|
|
|
|
opt = def ;
|
|
assert ( !def ) ;
|
|
// previous value (copy of 'v') destroyed from within 'opt'.
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_move_equal_optional]
|
|
|
|
[: `optional& optional<T>::operator= ( optional&& rhs ) noexcept(`['see below]`);`]
|
|
|
|
* [*Requires:] `T` is __MOVE_CONSTRUCTIBLE__ and `MoveAssignable`.
|
|
* [*Effects:]
|
|
[table
|
|
[]
|
|
[[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
|
|
[[[*`rhs` contains a value]][assigns `std::move(*rhs)` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `std::move(*rhs)`]]
|
|
[[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
|
|
]
|
|
* [*Returns:] `*this`;
|
|
* [*Postconditions:] `bool(rhs) == bool(*this)`.
|
|
* [*Remarks:] The expression inside `noexcept` is equivalent to `is_nothrow_move_constructible<T>::value && is_nothrow_move_assignable<T>::value`.
|
|
* [*Exception Safety:] If any exception is thrown, the initialization state of `*this` and `rhs` remains unchanged. If an exception is
|
|
thrown during the call to `T`'s move constructor, the state of `*rhs` is determined by the exception safety guarantee
|
|
of `T`'s move constructor. If an exception is thrown during the call to T's move-assignment, the state of `**this` and `*rhs` is determined by the exception safety guarantee of T's move assignment.
|
|
* [*Example:]
|
|
``
|
|
optional<T> opt(T(2)) ;
|
|
optional<T> def ;
|
|
|
|
opt = def ;
|
|
assert ( def ) ;
|
|
assert ( opt ) ;
|
|
assert ( *opt == T(2) ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
|
|
[#reference_optional_operator_equal_other_optional]
|
|
|
|
[: `template<U> optional& optional<T>::operator= ( optional<U> const& rhs ) ;`]
|
|
|
|
* [*Effect:]
|
|
[table
|
|
[]
|
|
[[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
|
|
[[[*`rhs` contains a value]][assigns `*rhs` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `*rhs`]]
|
|
[[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
|
|
]
|
|
* [*Returns:] `*this`.
|
|
* [*Postconditions:] `bool(rhs) == bool(*this)`.
|
|
* [*Exception Safety:] If any exception is thrown, the result of the expression `bool(*this)` remains unchanged.
|
|
If an exception is thrown during the call to `T`'s constructor, no effect.
|
|
If an exception is thrown during the call to `T`'s assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt0(v);
|
|
optional<U> opt1;
|
|
|
|
opt1 = opt0 ;
|
|
assert ( *opt1 == static_cast<U>(v) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_move_equal_other_optional]
|
|
|
|
[: `template<U> optional& optional<T>::operator= ( optional<U>&& rhs ) ;`]
|
|
|
|
* [*Effect:]
|
|
[table
|
|
[]
|
|
[[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
|
|
[[[*`rhs` contains a value]][assigns `std::move(*rhs)` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `std::move(*rhs)`]]
|
|
[[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
|
|
]
|
|
* [*Returns:] `*this`.
|
|
* [*Postconditions:] `bool(rhs) == bool(*this)`.
|
|
* [*Exception Safety:] If any exception is thrown, the result of the expression `bool(*this)` remains unchanged.
|
|
If an exception is thrown during the call to `T`'s constructor, no effect.
|
|
If an exception is thrown during the call to `T`'s assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt0(v);
|
|
optional<U> opt1;
|
|
|
|
opt1 = std::move(opt0) ;
|
|
assert ( opt0 );
|
|
assert ( opt1 )
|
|
assert ( *opt1 == static_cast<U>(v) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_emplace]
|
|
|
|
[: `template<class... Args> void optional<T>::emplace( Args&&... args );`]
|
|
|
|
* [*Requires:] The compiler supports rvalue references and variadic templates.
|
|
* [*Effect:] If `*this` is initialized calls `*this = none`.
|
|
Then initializes in-place the contained value as if direct-initializing an object
|
|
of type `T` with `std::forward<Args>(args)...`.
|
|
* [*Postconditions: ] `*this` is [_initialized].
|
|
* [*Throws:] Whatever the selected `T`'s constructor throws.
|
|
* [*Exception Safety:] If an exception is thrown during the initialization of `T`, `*this` is ['uninitialized].
|
|
* [*Notes:] `T` need not be __MOVE_CONSTRUCTIBLE__ or `MoveAssignable`. On compilers that do not suppor variadic templates or rvalue references, this function is available in limited functionality. For details [link optional_emplace_workaround see here].
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<const T> opt;
|
|
opt.emplace(0); // create in-place using ctor T(int)
|
|
opt.emplace(); // destroy previous and default-construct another T
|
|
opt.emplace(v); // destroy and copy-construct in-place (no assignment called)
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_equal_factory]
|
|
|
|
[: `template<InPlaceFactory> optional<T>& optional<T>::operator=( InPlaceFactory const& f );`]
|
|
[: `template<TypedInPlaceFactory> optional<T>& optional<T>::operator=( TypedInPlaceFactory const& f );`]
|
|
|
|
* [*Effect:] Assigns an `optional` with a value of `T` obtained from the
|
|
factory.
|
|
* [*Postconditions: ] `*this` is [_initialized] and its value is ['directly given]
|
|
from the factory `f` (i.e., the value [_is not copied]).
|
|
* [*Throws:] Whatever the `T` constructor called by the factory throws.
|
|
* [*Notes:] See [link boost_optional.tutorial.in_place_factories In-Place Factories]
|
|
* [*Exception Safety:] Exceptions can only be thrown during the call to
|
|
the `T` constructor used by the factory; in that case, the `optional` object
|
|
will be reset to be ['uninitialized].
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_reset_value]
|
|
|
|
[: `void optional<T>::reset( T const& v ) ;`]
|
|
* [*Deprecated:] same as `operator= ( T const& v) ;`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_reset]
|
|
|
|
[: `void optional<T>::reset() noexcept ;`]
|
|
* [*Effects:] Same as `operator=( none_t );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get]
|
|
|
|
[: `T const& optional<T>::get() const ;`]
|
|
[: `T& optional<T>::get() ;`]
|
|
|
|
[: `inline T const& get ( optional<T> const& ) ;`]
|
|
[: `inline T& get ( optional<T> &) ;`]
|
|
|
|
* [*Requires:] `*this` is initialized
|
|
* [*Returns:] A reference to the contained value
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_asterisk]
|
|
|
|
[: `T const& optional<T>::operator*() const& ;`]
|
|
[: `T& optional<T>::operator*() &;`]
|
|
|
|
* [*Requires:] `*this` is initialized
|
|
* [*Returns:] A reference to the contained value
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`. On compilers that do not support ref-qualifiers on member functions these two overloads are replaced with the classical two: a `const` and non-`const` member functions.
|
|
* [*Example:]
|
|
``
|
|
T v ;
|
|
optional<T> opt ( v );
|
|
T const& u = *opt;
|
|
assert ( u == v ) ;
|
|
T w ;
|
|
*opt = w ;
|
|
assert ( *opt == w ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_asterisk_move]
|
|
|
|
[: `T&& optional<T>::operator*() &&;`]
|
|
|
|
* [*Requires:] `*this` contains a value.
|
|
* [*Effects:] Equivalent to `return std::move(*val);`.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`. On compilers that do not support ref-qualifiers on member functions this overload is not present.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_value]
|
|
|
|
[: `T const& optional<T>::value() const& ;`]
|
|
[: `T& optional<T>::value() & ;`]
|
|
|
|
* [*Effects:] Equivalent to `return bool(*this) ? *val : throw bad_optional_access();`.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions these two overloads are replaced with the classical two: a `const` and non-`const` member functions.
|
|
* [*Example:]
|
|
``
|
|
T v ;
|
|
optional<T> o0, o1 ( v );
|
|
assert ( o1.value() == v );
|
|
|
|
try {
|
|
o0.value(); // throws
|
|
assert ( false );
|
|
}
|
|
catch(bad_optional_access&) {
|
|
assert ( true );
|
|
}
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_value_move]
|
|
|
|
[: `T&& optional<T>::value() && ;`]
|
|
|
|
* [*Effects:] Equivalent to `return bool(*this) ? std::move(*val) : throw bad_optional_access();`.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
|
|
|
|
__SPACE__
|
|
|
|
|
|
[#reference_optional_value_or]
|
|
|
|
[: `template<class U> T optional<T>::value_or(U && v) const& ;`]
|
|
|
|
* [*Effects:] Equivalent to `if (*this) return **this; else return std::forward<U>(v);`.
|
|
* [*Remarks:] If `T` is not __COPY_CONSTRUCTIBLE__ or `U &&` is not convertible to `T`, the program is ill-formed.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is replaced with the `const`-qualified member function. On compilers without rvalue reference support the type of `v` becomes `U const&`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_value_or_move]
|
|
|
|
[: `template<class U> T optional<T>::value_or(U && v) && ;`]
|
|
|
|
* [*Effects:] Equivalent to `if (*this) return std::move(**this); else return std::forward<U>(v);`.
|
|
* [*Remarks:] If `T` is not __MOVE_CONSTRUCTIBLE__ or `U &&` is not convertible to `T`, the program is ill-formed.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_value_or_call]
|
|
|
|
[: `template<class F> T optional<T>::value_or_eval(F f) const& ;`]
|
|
|
|
* [*Requires:] `T` is __COPY_CONSTRUCTIBLE__ and `F` models a __SGI_GENERATOR__ whose result type is convertible to `T`.
|
|
* [*Effects:] `if (*this) return **this; else return f();`.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is replaced with the `const`-qualified member function.
|
|
* [*Example:]
|
|
``
|
|
int complain_and_0()
|
|
{
|
|
clog << "no value returned, using default" << endl;
|
|
return 0;
|
|
}
|
|
|
|
optional<int> o1 = 1;
|
|
optional<int> oN = none;
|
|
|
|
int i = o1.value_or_eval(complain_and_0); // fun not called
|
|
assert (i == 1);
|
|
|
|
int j = oN.value_or_eval(complain_and_0); // fun called
|
|
assert (i == 0);
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_value_or_call_move]
|
|
|
|
[: `template<class F> T optional<T>::value_or_eval(F f) && ;`]
|
|
|
|
* [*Requires:] `T` is __MOVE_CONSTRUCTIBLE__ and `F` models a __SGI_GENERATOR__ whose result type is convertible to `T`.
|
|
* [*Effects:] `if (*this) return std::move(**this); else return f();`.
|
|
* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_map]
|
|
|
|
[: `template<class F> auto optional<T>::map(F f) const& -> `['see below]` ;`]
|
|
[: `template<class F> auto optional<T>::map(F f) & -> `['see below]` ;`]
|
|
|
|
* [*Effects:] `if (*this) return f(**this); else return none;`
|
|
* [*Notes:] The return type of these overloads is `optional<decltype(f(**this))>`. On compilers that do not support ref-qualifiers on member functions, these two (as well as the next one) overloads are replaced with good old const and non-const overloads.
|
|
* [*Example:]
|
|
``
|
|
auto length = [](const string& s){ return s.size(); };
|
|
optional<string> o1 {}, o2 {"cat"};
|
|
optional<size_t> os1 = o1.map(length), os2 = o2.map(length);
|
|
assert ( !os1 ) ;
|
|
assert ( os2 ) ;
|
|
assert ( *os2 == 3 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_map_move]
|
|
|
|
[: `template<class F> auto optional<T>::map(F f) && -> `['see below]` ;`]
|
|
|
|
* [*Effects:] `if (*this) return f(std::move(**this)); else return none;`
|
|
* [*Notes:] The return type of this overload is `optional<decltype(f(istd::move(**this)))>`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_flat_map]
|
|
|
|
[: `template<class F> auto optional<T>::flat_map(F f) const& -> `['see below]` ;`]
|
|
[: `template<class F> auto optional<T>::flat_map(F f) & -> `['see below]` ;`]
|
|
|
|
* [*Requires:] The return type of expression `f(**this)` is `optional<U>` for some object or reference type `U`.
|
|
* [*Effects:] `if (*this) return f(**this); else return none;`
|
|
* [*Notes:] The return type of these overloads is `optional<U>`. On compilers that do not support ref-qualifiers on member functions, these two (as well as the next one) overloads are replaced with good old const and non-const overloads.
|
|
* [*Example:]
|
|
``
|
|
optional<char> first_char(const string& s) {
|
|
return s.empty() ? none : optional<char>(s[0]);
|
|
};
|
|
optional<string> o1 {}, o2 {"cat"};
|
|
optional<char> os1 = o1.flat_map(first_char), os2 = o2.flat_map(first_char);
|
|
assert ( !os1 ) ;
|
|
assert ( os2 ) ;
|
|
assert ( *os2 == 'c' ) ;
|
|
``
|
|
__SPACE__
|
|
|
|
[#reference_optional_flat_map_move]
|
|
|
|
[: `template<class F> auto optional<T>::flat_map(F f) && -> `['see below]` ;`]
|
|
|
|
* [*Requires:] The return type of expression `f(std::move(**this))` is `optional<U>` for some object or reference type `U`.
|
|
* [*Effects:] `if (*this) return f(std::move(**this)); else return none;`
|
|
* [*Notes:] The return type of this overload is `optional<U>`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get_value_or_value]
|
|
|
|
[: `T const& optional<T>::get_value_or( T const& default) const ;`]
|
|
[: `T& optional<T>::get_value_or( T& default ) ;`]
|
|
|
|
* [*Deprecated:] Use `value_or()` instead.
|
|
* [*Returns:] A reference to the contained value, if any, or `default`.
|
|
* [*Throws:] Nothing.
|
|
* [*Example:]
|
|
``
|
|
T v, z ;
|
|
optional<T> def;
|
|
T const& y = def.get_value_or(z);
|
|
assert ( y == z ) ;
|
|
|
|
optional<T> opt ( v );
|
|
T const& u = opt.get_value_or(z);
|
|
assert ( u == v ) ;
|
|
assert ( u != z ) ;
|
|
``
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_get_ptr]
|
|
|
|
[: `T const* optional<T>::get_ptr() const ;`]
|
|
[: `T* optional<T>::get_ptr() ;`]
|
|
|
|
* [*Returns:] If `*this` is initialized, a pointer to the contained value;
|
|
else `0` (['null]).
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The contained value is permanently stored within `*this`, so you
|
|
should not hold nor delete this pointer
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
optional<T> opt(v);
|
|
optional<T> const copt(v);
|
|
T* p = opt.get_ptr() ;
|
|
T const* cp = copt.get_ptr();
|
|
assert ( p == get_pointer(opt) );
|
|
assert ( cp == get_pointer(copt) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_arrow]
|
|
|
|
[: `T const* optional<T>::operator ->() const ;`]
|
|
[: `T* optional<T>::operator ->() ;`]
|
|
|
|
* [*Requires: ] `*this` is initialized.
|
|
* [*Returns:] A pointer to the contained value.
|
|
* [*Throws:] Nothing.
|
|
* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
|
|
* [*Example:]
|
|
``
|
|
struct X { int mdata ; } ;
|
|
X x ;
|
|
optional<X> opt (x);
|
|
opt->mdata = 2 ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_bool]
|
|
|
|
[: `explicit optional<T>::operator bool() const noexcept ;`]
|
|
[: `bool optional<T>::has_value() const noexcept ;`]
|
|
|
|
* [*Returns:] `get_ptr() != 0`.
|
|
* [*Notes:] On compilers that do not support explicit conversion operators this falls back to safe-bool idiom.
|
|
* [*Example:]
|
|
``
|
|
optional<T> def ;
|
|
assert ( def == 0 );
|
|
optional<T> opt ( v ) ;
|
|
assert ( opt );
|
|
assert ( opt != 0 );
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_operator_not]
|
|
|
|
[: `bool optional<T>::operator!() noexcept ;`]
|
|
|
|
* [*Returns:] If `*this` is uninitialized, `true`; else `false`.
|
|
* [*Notes:] This operator is provided for those compilers which can't
|
|
use the ['unspecified-bool-type operator] in certain boolean contexts.
|
|
* [*Example:]
|
|
``
|
|
optional<T> opt ;
|
|
assert ( !opt );
|
|
*opt = some_T ;
|
|
|
|
// Notice the "double-bang" idiom here.
|
|
assert ( !!opt ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_is_initialized]
|
|
|
|
[: `bool optional<T>::is_initialized() const ;`]
|
|
|
|
* [*Deprecated:] Same as `explicit operator bool () ;`
|
|
|
|
|
|
[endsect]
|
|
|
|
[section Detailed Semantics - Optional References]
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_default_ctor]
|
|
|
|
[: `optional<T&>::optional() noexcept;`]
|
|
[: `optional<T&>::optional(none_t) noexcept;`]
|
|
|
|
* [*Postconditions:] `bool(*this) == false`; `*this` refers to nothing.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_value_ctor]
|
|
|
|
[: `template<class R> optional<T&>::optional(R&& r) noexcept;`]
|
|
* [*Postconditions:] `bool(*this) == true`; `addressof(**this) == addressof(r)`.
|
|
* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This constructor does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
|
|
* [*Notes:] This constructor is declared `explicit` on compilers that do not correctly suport binding to const lvalues of integral types. For more details [link optional_reference_binding see here].
|
|
* [*Example:]
|
|
``
|
|
T v;
|
|
T& vref = v ;
|
|
optional<T&> opt(vref);
|
|
assert ( *opt == v ) ;
|
|
++ v ; // mutate referee
|
|
assert (*opt == v);
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_cond_value_ctor]
|
|
|
|
[: `template<class R> optional<T&>::optional(bool cond, R&& r) noexcept;`]
|
|
* [*Effects: ] Initializes `ref` with expression `cond ? addressof(r) : nullptr`.
|
|
* [*Postconditions:] `bool(*this) == cond`; If `bool(*this)`, `addressof(**this) == addressof(r)`.
|
|
* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This constructor does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_copy_ctor]
|
|
|
|
[: `optional<T&>::optional ( optional const& rhs ) noexcept ;`]
|
|
|
|
* [*Effects: ] Initializes `ref` with expression `rhs.ref`.
|
|
|
|
* [*Postconditions:] `bool(*this) == bool(rhs)`.
|
|
|
|
* [*Example:]
|
|
``
|
|
optional<T&> uninit ;
|
|
assert (!uninit);
|
|
|
|
optional<T&> uinit2 ( uninit ) ;
|
|
assert ( uninit2 == uninit );
|
|
|
|
T v = 2 ; T& ref = v ;
|
|
optional<T> init(ref);
|
|
assert ( *init == v ) ;
|
|
|
|
optional<T> init2 ( init ) ;
|
|
assert ( *init2 == v ) ;
|
|
|
|
v = 3 ;
|
|
|
|
assert ( *init == 3 ) ;
|
|
assert ( *init2 == 3 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_ctor_from_opt_U]
|
|
|
|
[: `template<class U> explicit optional<T&>::optional ( optional<U&> const& rhs ) noexcept ;`]
|
|
|
|
* [*Requires:] `is_convertible<U&, T&>::value` is `true`.
|
|
|
|
* [*Effects: ] Initializes `ref` with expression `rhs.ref`.
|
|
|
|
* [*Postconditions:] `bool(*this) == bool(rhs)`.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_assign_none_t]
|
|
|
|
[: `optional<T&>::operator= ( none_t ) noexcept ;`]
|
|
|
|
* [*Effects: ] Assigns `ref` with expression `nullptr`.
|
|
|
|
* [*returns:] `*this`.
|
|
|
|
* [*Postconditions:] `bool(*this) == false`.
|
|
|
|
|
|
|
|
[#reference_optional_ref_copy_assign]
|
|
|
|
[: `optional& optional<T&>::operator= ( optional const& rhs ) noexcept ;`]
|
|
|
|
* [*Effects: ] Assigns `ref` with expression `rhs.ref`.
|
|
|
|
* [*returns:] `*this`.
|
|
|
|
* [*Postconditions:] `bool(*this) == bool(rhs)`.
|
|
|
|
* [*Notes:] This behaviour is called ['rebinding semantics]. See [link boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references here] for details.
|
|
|
|
* [*Example:]
|
|
``
|
|
int a = 1 ;
|
|
int b = 2 ;
|
|
T& ra = a ;
|
|
T& rb = b ;
|
|
optional<int&> def ;
|
|
optional<int&> ora(ra) ;
|
|
optional<int&> orb(rb) ;
|
|
|
|
def = orb ; // binds 'def' to 'b' through 'rb' wrapped within 'orb'
|
|
assert ( *def == b ) ;
|
|
*def = ora ; // changes the value of 'b' to a copy of the value of 'a'
|
|
assert ( b == a ) ;
|
|
int c = 3;
|
|
int& rc = c ;
|
|
optional<int&> orc(rc) ;
|
|
ora = orc ; // REBINDS ora to 'c' through 'rc'
|
|
c = 4 ;
|
|
assert ( *ora == 4 ) ;
|
|
``
|
|
|
|
|
|
[#reference_optional_ref_assign_optional_U]
|
|
|
|
[: `template<class U> optional& optional<T&>::operator= ( optional<U&> const& rhs ) noexcept ;`]
|
|
|
|
* [*Requires:] `is_convertible<U&, T&>::value` is `true`.
|
|
|
|
* [*Effects: ] Assigns `ref` with expression `rhs.ref`.
|
|
|
|
* [*returns:] `*this`.
|
|
|
|
* [*Postconditions:] `bool(*this) == bool(rhs)`.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_assign_R]
|
|
|
|
[: `template<class R> optional& optional<T&>::operator= ( R&& r ) noexcept ;`]
|
|
|
|
* [*Effects: ] Assigns `ref` with expression `r`.
|
|
|
|
* [*returns:] `*this`.
|
|
|
|
* [*Postconditions:] `bool(*this) == true`.
|
|
|
|
* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This function does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
|
|
|
|
* [*Example:]
|
|
``
|
|
int a = 1 ;
|
|
int b = 2 ;
|
|
T& ra = a ;
|
|
T& rb = b ;
|
|
optional<int&> def ;
|
|
optional<int&> opt(ra) ;
|
|
|
|
def = rb ; // binds 'def' to 'b' through 'rb'
|
|
assert ( *def == b ) ;
|
|
*def = a ; // changes the value of 'b' to a copy of the value of 'a'
|
|
assert ( b == a ) ;
|
|
int c = 3;
|
|
int& rc = c ;
|
|
opt = rc ; // REBINDS to 'c' through 'rc'
|
|
c = 4 ;
|
|
assert ( *opt == 4 ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_emplace_R]
|
|
|
|
[: `void optional<T&>::emplace( R&& r ) noexcept ;`]
|
|
* [*Effects: ] Assigns `ref` with expression `r`.
|
|
* [*Postconditions:] `bool(*this) == true`.
|
|
* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This function does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_get]
|
|
[: `T& optional<T&>::get() const ;`]
|
|
[: `T& optional<T&>::operator *() const ;`]
|
|
* [*Requires:] `bool(*this) == true`.
|
|
* [*Effects: ] Returns `*ref`.
|
|
* [*Throws: ] Nothing.
|
|
* [*Example:]
|
|
``
|
|
T v ;
|
|
T& vref = v ;
|
|
optional<T&> opt ( vref );
|
|
T const& vref2 = *opt;
|
|
assert ( vref2 == v ) ;
|
|
++ v ;
|
|
assert ( *opt == v ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_arrow]
|
|
[: `T* optional<T&>::operator -> () const ;`]
|
|
* [*Requires:] `bool(*this) == true`.
|
|
* [*Effects: ] Returns `ref`.
|
|
* [*Throws: ] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_value]
|
|
[: `T& optional<T&>::value() const ;`]
|
|
* [*Effects:] Equivalent to `return bool(*this) ? *val : throw bad_optional_access();`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_value_or]
|
|
[: `template<class R> T& optional<T&>::value_or( R&& r ) const noexcept;`]
|
|
* [*Effects:] Equivalent to `if (*this) return **this; else return r;`.
|
|
* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_value_or_eval]
|
|
[: `template<class F> T& optional<T&>::value_or( F f ) const ;`]
|
|
* [*Effects:] Equivalent to `if (*this) return **this; else return f();`.
|
|
* [*Remarks:] Unless `decltype(f())` is an lvalue reference, the program is ill-formed.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_map]
|
|
[: `template<class F> auto optional<T&>::map( F f ) const -> `['see below]`;`]
|
|
* [*Effects:] Equivalent to `if (*this) return f(**this); else return none;`.
|
|
* [*Remarks:] The return type of this function is `optional<decltype(f(**this))>`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_flat_map]
|
|
[: `template<class F> auto optional<T&>::flat_map( F f ) const -> `['see below]`;`]
|
|
* [*Requires:] The return type of expression `f(**this)` is `optional<U>` for some object or reference type `U`.
|
|
* [*Effects:] Equivalent to `if (*this) return f(**this); else return none;`.
|
|
* [*Remarks:] The return type of this function is `optional<U>`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_get_ptr]
|
|
[: `T* optional<T&>::get_ptr () const noexcept;`]
|
|
* [*Returns:] `ref`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_operator_bool]
|
|
[: `bool has_value() const noexcept;`]
|
|
[: `optional<T&>::operator bool () const noexcept;`]
|
|
* [*Returns:] `bool(ref)`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_operator_not]
|
|
[: `optional<T&>::operator ! () const noexcept;`]
|
|
* [*Returns:] `!bool(ref)`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_reset]
|
|
[: `void optional<T&>::reset() noexcept;`]
|
|
* [*Effects:] Same as `*this = none`.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_reset_value]
|
|
[: `template<class R> void optional<T&>::reset ( R&& r) noexcept;`]
|
|
* [*Effects:] Equivalent to `*this = std::forward<R>(r)`.
|
|
* [*Remarks:] This function is depprecated.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_is_initialized]
|
|
[: `bool optional<T&>::is_initialized() const noexcept;`]
|
|
* [*Effects:] Equivalent to `return bool(*this)`.
|
|
* [*Remarks:] This function is depprecated.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_optional_ref_get_value_or_value]
|
|
[: `template<class R> T& optional<T&>::get_value_or( R&& r ) const noexcept;`]
|
|
* [*Effects:] Equivalent to `return value_or(std::forward<R>(r);`.
|
|
* [*Remarks:] This function is depprecated.
|
|
|
|
[endsect]
|
|
|
|
|
|
[section Detailed Semantics - Free Functions]
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_value]
|
|
|
|
[: `optional<T> make_optional( T const& v )`]
|
|
|
|
* [*Returns: ] `optional<T>(v)` for the ['deduced] type `T` of `v`.
|
|
* [*Example:]
|
|
``
|
|
template<class T> void foo ( optional<T> const& opt ) ;
|
|
|
|
foo ( make_optional(1+1) ) ; // Creates an optional<int>
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_rvalue]
|
|
|
|
[: `optional<std::decay_t<T>> make_optional( T && v )`]
|
|
|
|
* [*Returns: ] `optional<std::decay_t<T>>(std::move(v))` for the ['deduced] type `T` of `v`.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_bool_value]
|
|
|
|
[: `optional<T> make_optional( bool condition, T const& v )`]
|
|
|
|
* [*Returns: ] `optional<T>(condition, v)` for the ['deduced] type `T` of `v`.
|
|
* [*Example:]
|
|
``
|
|
optional<double> calculate_foo()
|
|
{
|
|
double val = compute_foo();
|
|
return make_optional(is_not_nan_and_finite(val),val);
|
|
}
|
|
|
|
optional<double> v = calculate_foo();
|
|
if ( !v )
|
|
error("foo wasn't computed");
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_make_optional_bool_rvalue]
|
|
|
|
[: `optional<std::decay_t<T>> make_optional( bool condition, T && v )`]
|
|
|
|
* [*Returns: ] `optional<std::decay_t<T>>(condition, std::move(v))` for the ['deduced] type `T` of `v`.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_equal_optional_optional]
|
|
|
|
[: `bool operator == ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Requires:] `T` shall meet requirements of __SGI_EQUALITY_COMPARABLE__.
|
|
* [*Returns:] If both `x` and `y` are initialized, `(*x == *y)`. If only
|
|
`x` or `y` is initialized, `false`. If both are uninitialized, `true`.
|
|
* [*Notes:] This definition guarantees that `optional<T>` not containing a value is compared unequal to any `optional<T>` containing any value, and equal to any other `optional<T>` not containing a value.
|
|
Pointers have shallow relational operators while `optional` has deep relational operators. Do not use `operator==` directly in generic code which expect to be given either an `optional<T>` or a pointer; use
|
|
__FUNCTION_EQUAL_POINTEES__ instead
|
|
* [*Example:]
|
|
``
|
|
optional<T> oN, oN_;
|
|
optional<T> o1(T(1)), o1_(T(1));
|
|
optional<T> o2(T(2));
|
|
|
|
assert ( oN == oN ); // Identity implies equality
|
|
assert ( o1 == o1 ); //
|
|
|
|
assert ( oN == oN_ ); // Both uninitialized compare equal
|
|
|
|
assert ( oN != o1 ); // Initialized unequal to initialized.
|
|
|
|
assert ( o1 == o1_ ); // Both initialized compare as (*lhs == *rhs)
|
|
assert ( o1 != o2 ); //
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_less_optional_optional]
|
|
|
|
[: `bool operator < ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Requires:] Expression `*x < *y` shall be well-formed and its result shall be convertible to `bool`.
|
|
* [*Returns:] `(!y) ? false : (!x) ? true : *x < *y`.
|
|
* [*Notes:] This definition guarantees that `optional<T>` not containing a value is ordered as less than any `optional<T>` containing any value, and equivalent to any other `optional<T>` not containing a value.
|
|
Pointers have shallow relational operators while `optional` has deep relational operators. Do not use `operator<` directly in generic code
|
|
which expect to be given either an `optional<T>` or a pointer; use __FUNCTION_LESS_POINTEES__ instead. `T` need not be __SGI_LESS_THAN_COMPARABLE__. Only single `operator<` is required. Other relational operations are defined in terms of this one. If `T`'s `operator<` satisfies the axioms of __SGI_LESS_THAN_COMPARABLE__ (transitivity, antisymmetry and irreflexivity), `optinal<T>` is __SGI_LESS_THAN_COMPARABLE__.
|
|
* [*Example:]
|
|
``
|
|
optional<T> oN, oN_;
|
|
optional<T> o0(T(0));
|
|
optional<T> o1(T(1));
|
|
|
|
assert ( !(oN < oN) ); // Identity implies equivalence
|
|
assert ( !(o1 < o1) );
|
|
|
|
assert ( !(oN < oN_) ); // Two uninitialized are equivalent
|
|
assert ( !(oN_ < oN) );
|
|
|
|
assert ( oN < o0 ); // Uninitialized is less than initialized
|
|
assert ( !(o0 < oN) );
|
|
|
|
assert ( o1 < o2 ) ; // Two initialized compare as (*lhs < *rhs)
|
|
assert ( !(o2 < o1) ) ;
|
|
assert ( !(o2 < o2) ) ;
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_not_equal_optional_optional]
|
|
|
|
[: `bool operator != ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( x == y );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_greater_optional_optional]
|
|
|
|
[: `bool operator > ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `( y < x );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_less_or_equal_optional_optional]
|
|
|
|
[: `bool operator <= ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( y < x );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_greater_or_equal_optional_optional]
|
|
|
|
[: `bool operator >= ( optional<T> const& x, optional<T> const& y );`]
|
|
|
|
* [*Returns: ] `!( x < y );`
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_equal_optional_none]
|
|
|
|
[: `bool operator == ( optional<T> const& x, none_t ) noexcept;`]
|
|
[: `bool operator == ( none_t, optional<T> const& x ) noexcept;`]
|
|
|
|
* [*Returns:] `!x`.
|
|
* [*Notes:] `T` need not meet requirements of __SGI_EQUALITY_COMPARABLE__.
|
|
|
|
|
|
__SPACE__
|
|
|
|
[#reference_operator_compare_not_equal_optional_none]
|
|
|
|
[: `bool operator != ( optional<T> const& x, none_t ) noexcept;`]
|
|
[: `bool operator != ( none_t, optional<T> const& x ) noexcept;`]
|
|
|
|
* [*Returns: ] `bool(x);`
|
|
|
|
|
|
__SPACE__
|
|
|
|
|
|
[#reference_free_get_pointer]
|
|
[: `auto get_pointer ( optional<T>& o ) -> typename optional<T>::pointer_type ;`]
|
|
[: `auto get_pointer ( optional<T> const& o ) -> typename optional<T>::pointer_const_type ;`]
|
|
* [*Returns:] `o.get_ptr()`.
|
|
* [*Throws:] Nothing.
|
|
|
|
__SPACE__
|
|
|
|
|
|
[#reference_free_get_value_or]
|
|
[: `auto get_optional_value_or ( optional<T>& o, typename optional<T>::reference_type def ) -> typename optional<T>::reference_type ;`]
|
|
[: `auto get_optional_value_or ( optional<T> const& o, typename optional<T>::reference_const_type def ) -> typename optional<T>::reference_const_type ;`]
|
|
* [*Returns:] `o.get_value_or(def)`.
|
|
* [*Throws:] Nothing.
|
|
* [*Remarks:] This function is deprecated.
|
|
|
|
__SPACE__
|
|
|
|
[#reference_swap_optional_optional]
|
|
|
|
[: `void swap ( optional<T>& x, optional<T>& y ) ;`]
|
|
|
|
* [*Requires:] Lvalues of type `T` shall be swappable and `T` shall be __MOVE_CONSTRUCTIBLE__.
|
|
* [*Effects:]
|
|
[table
|
|
[]
|
|
[[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
|
|
[[[*`rhs` contains a value]][calls `swap(*(*this), *rhs)`][initializes the contained value of `*this` as if direct-initializing an object of type `T` with the expression `std::move(*rhs)`, followed by `rhs.val->T::~T()`, `*this` contains a value and `rhs` does not contain a value]]
|
|
[[[*`rhs` does not contain a value]][initializes the contained value of `rhs` as if direct-initializing an object of type `T` with the expression `std::move(*(*this))`, followed by `val->T::~T()`, `*this` does not contain a value and `rhs` contains a value][no effect]]
|
|
]
|
|
* [*Postconditions:] The states of `x` and `y` interchanged.
|
|
* [*Throws:] If both are initialized, whatever `swap(T&,T&)` throws. If only
|
|
one is initialized, whatever `T::T ( T&& )` throws.
|
|
* [*Example:]
|
|
``
|
|
T x(12);
|
|
T y(21);
|
|
optional<T> def0 ;
|
|
optional<T> def1 ;
|
|
optional<T> optX(x);
|
|
optional<T> optY(y);
|
|
|
|
boost::swap(def0,def1); // no-op
|
|
|
|
boost::swap(def0,optX);
|
|
assert ( *def0 == x );
|
|
assert ( !optX );
|
|
|
|
boost::swap(def0,optX); // Get back to original values
|
|
|
|
boost::swap(optX,optY);
|
|
assert ( *optX == y );
|
|
assert ( *optY == x );
|
|
``
|
|
|
|
__SPACE__
|
|
|
|
[#reference_swap_optional_reference]
|
|
[: `void swap ( optional<T&>& x, optional<T&>& y ) noexcept ;`]
|
|
|
|
* [*Postconditions:] `x` refers to what `y` refererred to before the swap (if anything). `y` refers to whatever `x` referred to before the swap.
|
|
|
|
* [*Example:]
|
|
``
|
|
T x(12);
|
|
T y(21);
|
|
|
|
optional<T&> opt0;
|
|
optional<T&> optX (x);
|
|
optional<T&> optY (y);
|
|
|
|
boost::swap(optX, optY);
|
|
assert (addressof(*optX) == addressof(y));
|
|
assert (addressof(*optY) == addressof(x));
|
|
|
|
boost::swap(opt0, optX);
|
|
assert ( opt0 );
|
|
assert ( !optX );
|
|
assert (addressof(*opt0) == addressof(y));
|
|
``
|
|
|
|
[endsect]
|