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)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Experimental

Technical Specification

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)

Experimental Non-TS

Pattern Matching

Linear Algebra

std::execution

Contracts

2D Graphics

 

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)