operator=(std::optional)

 

C++

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Utilities library

Type support (basic types, RTTI, type traits)

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Error handling

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Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

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swap

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declval (C++11)

 

std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator-> optional::operator*

optional::operator bool

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

Non-member functions

operator== operator<

make_optional

swap

Helper classes

hash

 

Defined in header <optional>
Compare two optional objects
template< class T > constexpr bool operator==( const optional<T>& lhs, const optional<T>& rhs );	(1)	(since C++14)
template< class T > constexpr bool operator<( const optional<T>& lhs, const optional<T>& rhs );	(2)	(since C++14)
Compare an optional object with a nullopt
template< class T > constexpr bool operator==( const optional<T>& opt, std::nullopt_t );	(3)	(since C++14)
template< class T > constexpr bool operator==( std::nullopt_t, const optional<T>& opt );	(4)	(since C++14)
template< class T > constexpr bool operator<( const optional<T>& opt, std::nullopt_t );	(5)	(since C++14)
template< class T > constexpr bool operator<( std::nullopt_t, const optional<T>& opt);	(6)	(since C++14)
Compare an optional object with a T
template< class T > constexpr bool operator==( const optional<T>& opt, const T& v );	(7)	(since C++14)
template< class T > constexpr bool operator==( const T& value, const optional<T>& opt );	(8)	(since C++14)
template< class T > constexpr bool operator<( const optional<T>& opt, const T& v );	(9)	(since C++14)

Performs comparison operations on optional objects.

1-2) Compares two optional objects, lhs and rhs. The contained values are compared only if both lhs and rhs are in engaged states. Otherwise,

• lhs is considered equal to rhs if, and only if, both lhs and rhs are in disengaged states.
• lhs is considered less than rhs if, and only if, rhs is in engaged state and lhs is not.

3-6) Compares opt with a nullopt. Equivalent to (1-2) when comparing to an optional with engaged state.

7-9) Compares opt with a value. The values are compared only if opt is in engaged state. Otherwise, opt is considered less than value.

Parameters

lhs, rhs, opt	-	an optional object to compare
value	-	value to compare to the contained value
Type requirements
- T must meet the requirements of EqualityComparable in order to use overloads (1, 7-8).

Return value

1) If bool(lhs) != bool(rhs), returns false

Otherwise, if bool(lhs) == bool(rhs) == false, returns true

Otherwise, returns *lhs == *rhs.

2) If bool(rhs) == false returns false

Otherwise, if lhs == false, returns true

Otherwise returns std::less<T>{}(*x, *y)

3) Returns !opt.

4) Returns false.

5) Returns !opt.

6) Returns bool(opt)

7-8) Returns bool(opt) ? *opt == value : false.

9) Returns bool(opt) ? std::less<T>{}(*opt, value) : true.

Exceptions

1-2) (none)

3-6)

noexcept specification:  

noexcept

  (since C++11)

7-9) (none)