operator==, !=, <, <=, >, >=(std::experimental::optional)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals TS v2)

Library fundamentals 3 (library fundamentals TS v3)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

Extensions for concurrency (concurrency TS)

Extensions for concurrency 2 (concurrency TS v2)

Concepts (concepts TS)

Ranges (ranges TS)

Reflection (reflection TS)

Mathematical special functions (special functions TR)

 

Library fundamentals

experimental::optional

experimental::any

experimental::basic_string_view

experimental::sample

experimental::shared_ptr

experimental::weak_ptr

experimental::apply

experimental::invocation_typeexperimental::raw_invocation_type

experimental::search

experimental::default_searcherexperimental::make_default_searcher

experimental::boyer_moore_searcherexperimental::make_boyer_moore_searcher

experimental::boyer_moore_horspool_searcherexperimental::make_boyer_moore_horspool_searcher

Type-erased and polymorphic allocators

Variable templates for type traits

 

std::experimental::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!=operator<operator<=operator>operator>=

make_optional

swap

Helper classes

hash

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

Defined in header <experimental/optional>
Compare two optional objects
template< class T > constexpr bool operator==( const optional<T>& lhs, const optional<T>& rhs );	(1)	(library fundamentals TS)
template< class T > constexpr bool operator!=( const optional<T>& lhs, const optional<T>& rhs );	(2)	(library fundamentals TS)
template< class T > constexpr bool operator<( const optional<T>& lhs, const optional<T>& rhs );	(3)	(library fundamentals TS)
template< class T > constexpr bool operator<=( const optional<T>& lhs, const optional<T>& rhs );	(4)	(library fundamentals TS)
template< class T > constexpr bool operator>( const optional<T>& lhs, const optional<T>& rhs );	(5)	(library fundamentals TS)
template< class T > constexpr bool operator>=( const optional<T>& lhs, const optional<T>& rhs );	(6)	(library fundamentals TS)
Compare an optional object with a nullopt
template< class T > constexpr bool operator==( const optional<T>& opt, std::nullopt_t ) noexcept;	(7)	(library fundamentals TS)
template< class T > constexpr bool operator==( std::nullopt_t, const optional<T>& opt ) noexcept;	(8)	(library fundamentals TS)
template< class T > constexpr bool operator!=( const optional<T>& opt, std::nullopt_t ) noexcept;	(9)	(library fundamentals TS)
template< class T > constexpr bool operator!=( std::nullopt_t, const optional<T>& opt ) noexcept;	(10)	(library fundamentals TS)
template< class T > constexpr bool operator<( const optional<T>& opt, std::nullopt_t ) noexcept;	(11)	(library fundamentals TS)
template< class T > constexpr bool operator<( std::nullopt_t, const optional<T>& opt ) noexcept;	(12)	(library fundamentals TS)
template< class T > constexpr bool operator<=( const optional<T>& opt, std::nullopt_t ) noexcept;	(13)	(library fundamentals TS)
template< class T > constexpr bool operator<=( std::nullopt_t, const optional<T>& opt ) noexcept;	(14)	(library fundamentals TS)
template< class T > constexpr bool operator>( const optional<T>& opt, std::nullopt_t ) noexcept;	(15)	(library fundamentals TS)
template< class T > constexpr bool operator>( std::nullopt_t, const optional<T>& opt ) noexcept;	(16)	(library fundamentals TS)
template< class T > constexpr bool operator>=( const optional<T>& opt, std::nullopt_t ) noexcept;	(17)	(library fundamentals TS)
template< class T > constexpr bool operator>=( std::nullopt_t, const optional<T>& opt ) noexcept;	(18)	(library fundamentals TS)
Compare an optional object with a T
template< class T > constexpr bool operator==( const optional<T>& opt, const T& value );	(19)	(library fundamentals TS)
template< class T > constexpr bool operator==( const T& value, const optional<T>& opt );	(20)	(library fundamentals TS)
template< class T > constexpr bool operator!=( const optional<T>& opt, const T& value );	(21)	(library fundamentals TS)
template< class T > constexpr bool operator!=( const T& value, const optional<T>& opt );	(22)	(library fundamentals TS)
template< class T > constexpr bool operator<( const optional<T>& opt, const T& value );	(23)	(library fundamentals TS)
template< class T > constexpr bool operator<( const T& value, const optional<T>& opt );	(24)	(library fundamentals TS)
template< class T > constexpr bool operator<=( const optional<T>& opt, const T& value );	(25)	(library fundamentals TS)
template< class T > constexpr bool operator<=( const T& value, const optional<T>& opt );	(26)	(library fundamentals TS)
template< class T > constexpr bool operator>( const optional<T>& opt, const T& value );	(27)	(library fundamentals TS)
template< class T > constexpr bool operator>( const T& value, const optional<T>& opt );	(28)	(library fundamentals TS)
template< class T > constexpr bool operator>=( const optional<T>& opt, const T& value );	(29)	(library fundamentals TS)
template< class T > constexpr bool operator>=( const T& value, const optional<T>& opt );	(30)	(library fundamentals TS)

Performs comparison operations on optional objects.

1-6) Compares two optional objects, lhs and rhs. The contained values are compared (using operator== for (1-2) and operator< for (3-6)) only if both lhs and rhs contain values. Otherwise,

• lhs is considered equal to rhs if, and only if, both lhs and rhs do not contain a value.
• lhs is considered less than rhs if, and only if, rhs contains a value and lhs does not.

7-18) Compares opt with a nullopt. Equivalent to (1-6) when comparing to an optional that does not contain a value.

19-30) Compares opt with a value. The values are compared (using operator== for (19-22) and operator< for (23-30)) only if opt contains a value. 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 (1-2).

Return value

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

Otherwise, if bool(lhs) == false (and so bool(rhs) == false as well), returns true.

Otherwise, returns *lhs == *rhs.

2) Returns !(lhs == rhs).

3) If bool(rhs) == false returns false.

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

Otherwise returns *x < *y.

4) Returns !(rhs < lhs).

5) Returns rhs < lhs.

6) Returns !(lhs < rhs).

7-8) Returns !opt.

9-10) Returns bool(opt).

11) Returns false.

12) Returns bool(opt).

13) Returns !opt.

14) Returns true.

15) Returns bool(opt).

16) Returns false.

17) Returns true.

18) Returns !opt.

19) Returns bool(opt) ? *opt == value : false.

20) Returns bool(opt) ? value == *opt : false.

21) Returns bool(opt) ? !(*opt == value) : true.

22) Returns bool(opt) ? !(value == *opt) : true.

23) Returns bool(opt) ? *opt < value  : true.

24) Returns bool(opt) ? value < *opt  : false.

25) Returns !(opt > value).

26) Returns !(value > opt).

27) Returns bool(opt) ? value < *opt  : false.

28) Returns bool(opt) ? *opt < value  : true.

29) Returns !(opt < value).

30) Returns !(value < opt).

Exceptions

1-6) (none)

19-30) (none)